Guidance For Applying ASCE 24
Guidance For Applying ASCE 24
Guidance For Applying ASCE 24
Table of Contents
1 Introduction ........................................................................................................................ 1
1.1 Unified HMA Program .................................................................................................. 1
1.2 ASCE 24 and the National Flood Insurance Program .................................................. 3
1.3 ASCE 24 and Its Applicability to HMA Flood Projects .................................................. 6
1.4 Preliminary Codes, Standards, and Ordinances Considerations .................................. 7
1.5 Organization of This Guidance ..................................................................................... 8
Appendices
Appendix A Deemed-to-Comply Table
Appendix B Benefit-Cost Considerations
Appendix C Mitigation Measure Selection Worksheet
Appendix D Checklists for Mitigation Projects: Development, Grant Applications,
Implementation, and Closeout
Appendix E References, Resources, and Links
Appendix F Acronyms and Abbreviations
Figures
Figure 2-1 Building elevated on piles (Source: FEMA 2012a) ..................................................11
Figure 2-2 Building satisfying NFIP minimum requirements compared with building
satisfying ASCE 24 requirements ...........................................................................12
Figure 2-3 Allowable foundation types in Zone A (Source: FEMA 2012c) ................................13
Figure 2-4 Lowest floor elevation requirements in Zone A .......................................................14
Figure 2-5 Foundation requirements in Coastal High Hazard Areas and Coastal A
Zones (Source: FEMA 2012c) ................................................................................18
Figure 2-6 Lowest floor elevation requirements for Coastal High Hazard Areas (Zone V)
and Coastal A Zones (Source: FEMA 2012c) Foundation Design
Requirements .........................................................................................................20
Figure 3-1 Types of flood shields (Source: FEMA 2012b) ........................................................29
Tables
Table 1-1 Eligible and Ineligible Project Types per the NFIP, ASCE 24, and HMA
Policies .................................................................................................................... 2
Table 1-2 Eligible Flood Mitigation Activities Organized by HMA Program for Project
Types Addressed in HMA Policy FP 203-074-1 Minimum Design Standards
for HMA Projects in Flood Hazard Areas ................................................................ 3
Table 2-1 Minimum Elevation of the Top of Lowest Floor Relative to BFE or DFE
Flood Hazard Areas Other Than Coastal High Hazard Areas and Coastal A
Zones .....................................................................................................................13
Table 2-2 Minimum Elevation, Relative to BFE for DFE, Below Which Flood Damage-
Resistant Materials Must Be Used in Zone A..........................................................16
Table 2-3 Minimum Elevation of Utilities and Attendant Equipment Relative to BFE or
DFE in Zone A........................................................................................................17
Table 2-4 Minimum Elevation of Bottom of Lowest Supporting Horizontal Structural
Member of Lowest Floor Relative to BFE or DFECoastal High Hazard
Areas and Coastal A Zones ....................................................................................19
Table 2-5 Minimum Elevation, Relative to BFE for DFE, Below Which Flood Damage-
Resistant Materials Must Be Used in Coastal High Hazard Areas and
Coastal A Zones .....................................................................................................23
Table 2-6 Minimum Elevation of Utilities and Attendant Equipment Relative to BFE or
DFE in Coastal High Hazard Areas and Coastal A Zones ......................................24
Table 3-1 Comparison of ASCE 24 and NFIP Dry Floodproofing Requirements.....................27
Table 3-2 Minimum Elevation of Floodproofing Relative to the BFE or DFE (based on
ASCE 24 Table 6-1) ...............................................................................................28
Table 4-1 Minimum Elevation of the Top of Lowest Floor Relative to BFE or DFE .................34
Table 4-2 Minimum Elevation, Below Which Flood Damage-Resistant Materials Must
Be Used .................................................................................................................36
Table 4-3 Minimum Elevation of Utilities and Attendant Equipment Relative to the BFE
or DFE....................................................................................................................36
1 Introduction
This document was prepared by the Federal Emergency Management Agency (FEMA) to assist
local governments, designers, and property owners. It identifies key design and construction
requirements in the American Society of Civil Engineers (ASCE) Structural Engineering
Institutes ASCE/SEI 24-05, Flood-Resistant Design and Construction (ASCE 24) that apply to
HMA flood mitigation grant projects. This document is in no way intended to be used in place of
ASCE 24 but rather as a companion to the standard. Designers, local officials, and others who
want to apply the standard still need to refer to the standard for complete requirements.
This document addresses the full range of structuresresidential and nonresidentialthat are
eligible for project assistance consideration under FEMAs Hazard Mitigation Assistance (HMA)
program and provides guidance on how ASCE 24 should be applied to structure elevation, dry
floodproofing, and mitigation reconstruction projects in flood hazard areas. Table 1-1 presents a
summary of permitted and not permitted residential and nonresidential mitigation projects per the
National Flood Insurance Program (NFIP), ASCE 24, and HMA policies. In this document,
HMA Policy refers to the existing HMA guidance, and HMA 24-05 Policy refers to
FP 203-074-1, Minimum Design Standards for HMA Projects in Flood Hazard Areas (FIMA
2013).
The guidance in this document does not advocate construction in the floodplain; rather, it is
intended to reduce hazard risk for situations in which there is no practicable alternative. The
emphasis of this document is on mitigation if construction in the floodplain is not avoidable,
although the best way to greatly reduce (if not eliminate) flood risk is to relocate a structure out
of the floodplain.
In this draft guidance document, the term must is used in the context of the ASCE 24 design
standard to indicate compliance to applicable criteria within ASCE 24.
Zone A HMA-G E E I2 E E* E*
HMA w/ASCE 24 E E I2 I3 E* E*
HMA w/ASCE 24 E E I2 I E* E*
Zone V NFIP E E I I E E
HMA-G E E I I I I
HMA w/ASCE 24 E E I I I I
E=eligible 1. Development in the floodway is only permitted if it can be demonstrated that it will not result in an
increase in the flood level or reduce the conveyance of the floodway for the base flood.
E*= eligible in FMA only
2. Residential structures determined to be historic buildings may be dry floodproofed and are not
I = Ineligible
subject to the SI/SD restriction.
SI/SD = Substantial Improvement/Damage
3. Ineligible where flood velocities exceed 5 feet/second.
= Other High-Risk Areas is a term used in ASCE 24
Relief and Emergency Assistance Act (Stafford Act) or the National Flood Insurance Act. All
mitigation projects must be cost effective and technically feasible. They must also meet
environmental planning and historic preservation requirements in accordance with HMA
Program requirements as well as all other applicable Federal statutes. FEMA requires that these
grant programs also comply with applicable local, State, or national building codes, standards,
and regulations. States, Territories, federally recognized Indian Tribal governments, and
communities are eligible for assistance provided by HMA Programs in both the pre- and post-
disaster time frames. These programs include the Hazard Mitigation Grant Program (HMGP),
Pre-Disaster Mitigation Program (PDM), and the Flood Mitigation Assistance Program (FMA).
Information on the background of the aforementioned programs, assistance, the award process
and administration, applicant and project eligibility, how to complete and submit an application,
application review, and program-specific guidance has been combined in a single document:
Hazard Mitigation Assistance Unified Guidance (HMA Unified Guidance). Although the latest
edition of this document was published in 2013, it is updated regularly and users should refer to
the most recent edition (see Appendix E). See Table 1-2 for a list of eligible projects by program.
Table 1-2. Eligible Flood Mitigation Activities Organized by HMA Program for Project Types Addressed in HMA Policy
FP 203-074-1 Minimum Design Standards for HMA Projects in Flood Hazard Areas
HMA Program
Eligible Activities HMGP PDM FMA
Structure Elevation
Dry Floodproofing of Historic Residential
Structures
Dry Floodproofing of Nonresidential Structures
Mitigation Reconstruction X X
Source: FEMA (2013)
ASCE 24. This is because project designers may not have all the information required to fully
apply ASCE 24, and/or the original structure may not have been designed in accordance with the
loads and conditions specified by ASCE 24.
Although complete compliance with ASCE 24 is preferred, certain provisions of ASCE 24 must
be met completely, and the intent of the remaining provisions must be met. Elevation and dry
floodproofing projects that meet this level of compliance will be deemed-to-comply with
ASCE 24. Appendix A, Deemed-to-Comply Table, summarizes the provisions of ASCE 24 and
what constitutes a deemed-to-comply project approach.
In ASCE 24, structures are classified according to Table 1-3. These classifications are referenced
throughout the standard, and requirements specific to each structure type are provided.
Table 1-3. ASCE/SEI 24-05 Table 1.1 Classification of Structures for Flood-Resistant Design and Construction
(Classification same as ASCE 7, Minimum Design Loads for Buildings and Other Structures)
building code. If no building code has been adopted for a community that participates in the
NFIP, permits are still required for development in SFHAs per NFIP regulations. Similarly, if
HMA assistance is being requested, the project is subject to HMA requirements and, thus, the
provisions of ASCE 24 as outlined in this document. For more information on permitting and
community-specific requirements, see Section 7.4.2.
This section offers guidance for designing and implementing building elevation mitigation
projects in accordance with ASCE 24 based on the location of the project site (Zone A or Coastal
High Hazard Area and Coastal A Zone).This section highlights the key provisions in ASCE 24
that apply to elevation projects. Elevation project types covered in this section include elevation
on continuous foundation walls; elevation on open foundations, such as piles, piers, posts, or
columns; and elevation on fill. Per HMA general guidance, any activity that results in the
construction of new living space at or above the BFE will only be considered when consistent
with the Mitigation Reconstruction requirements (see Section 4 of this document). Relevant
ASCE 24 design considerations for each of the applicable project types are addressed in Sections
2.1 and 2.2 of this document.
According to the NFIP regulations, in general, a structures lowest floor must be either elevated
or floodproofed to the BFE. However, States and communities may set higher elevation
standards than what is required by the NFIP, often by including freeboard requirements
(freeboard is a measure of safety usually expressed in feet above a flood level). Similar to the
requirements that may be set in communities, ASCE 24 also requires elevating many types of
structures to an elevation higher than the BFE. For any elevation project, the greater of the two
elevations must be followed (either the DFE required by the community or the minimum
elevation requirements from ASCE 24). The concepts of BFE, DFE, and freeboard are illustrated
in Figure 2-2.
Figure 2-2. Building satisfying NFIP minimum requirements compared with building satisfying ASCE 24 requirements
Pertinent ASCE 24 provisions are identified and their application to elevation mitigation projects
is explained in the following sections.
Table 2-1. Minimum Elevation of the Top of Lowest Floor Relative to BFE or DFE
Flood Hazard Areas Other Than Coastal High Hazard Areas and Coastal A Zones
For guidance on selecting the appropriate structure category, see Section 1.2 of this document.
Figure 2-4 shows the lowest floor elevation requirement for structures in Zone A. Any area
below the lowest floor must be used solely for parking, building access, or storage. Section 2.1.3
includes additional detail regarding requirements for enclosures below the lowest floor. The
exception to these requirements is dry floodproofed nonresidential buildings where the lowest
floor is permitted below the elevation specified in Table 2-1 because the lowest floor will be
beneath the level of the dry floodproofing protection. See Section 3 for applicable dry
floodproofing considerations.
and connection of the existing structure to the new foundation. Building elements located above
the foundation are not subject to the provisions of ASCE 24.
2.1.2.1 Slab-on-Grade
For elevation mitigation projects where a slab on grade foundation will be constructed to support
the structure, ASCE 24-05 Section 2.4 specifies that the slab must be placed on structural fill or
undisturbed soil with adequate bearing capacity. The design and construction of the fill must
account for consolidation of the underlying soil, differential settlement, and slope stability and
erosion control. ASCE 24 includes specific guidance for compaction and side slopes. The top of
any slab-on-grade foundation must be at or above the elevation specified in Table 2-1, and if the
slab has been turned down to act as footings, it must be designed to resist damage from scour and
erosion during a flooding event. In addition, the slab must not break up during design flood
conditions, and must be placed such that no supporting soil is lost during the design flood.
In the case where an existing home is supported on a slab-on-grade foundation, the two possible
elevation methods are to separate the home from the slab and raise the home or to keep the home
and slab intact and raise them both. In either situation, the ASCE 24 requirements apply as
described in this and the following sections for the new foundation type. In addition, if raising
the slab with the home, the new foundation system must include an elevated support structure to
accommodate the load of both the slab and the home.
however, designers should be aware that the size may affect flood insurance premiums. ASCE 24
has specific requirements for the size, number, location, and spacing of openings in any walls
that form an enclosure below the lowest floor of a structure situated in Zone A. Openings may be
engineered or non-engineered, but must prevent an imbalance of hydrostatic pressure (equivalent
to no more than 1 foot of variation in the water surface elevation inside and outside the enclosed
area). Breakaway wall enclosures in Zone A must have openings to allow for the automatic entry
and exit of floodwaters during design flood conditions, just as solid foundation walls must. The
design guidance provided in ASCE 24 will satisfy the elevation design standards of HMA Unified
Guidance, Part IX Additional Project Guidance, section titled Eligible Design Standards.
FEMA Technical Bulletin 1 (TB-1), Openings in Foundation Walls and Walls of Enclosures
(2008d); FEMA TB-5, Free-of-Obstruction Requirements (2008b); and FEMA TB-9, Design and
Construction Guidance for Breakaway Walls Below Elevated Coastal Buildings (2008a), offer
additional related guidance on enclosures below the DFE.
Table 2-2. Minimum Elevation, Relative to BFE for DFE, Below Which Flood
Damage-Resistant Materials Must Be Used in Zone A
Structure
Flood Hazard Areas
Category1
I DFE
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
1. See Table 1-3 in this document for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
Source: ASCE 24-05, Table 5-1
ASCE 24-05 Section 5.2 provides specific requirements for metal connectors and fasteners,
structural steel, concrete, masonry, wood and timber, and finishing materials. For elevation
mitigation projects where a portion of the existing foundation will remain and be reused, the
building materials requirements apply only to the new sections of the foundation. If the
foundation has been replaced in the mitigation project, then the material requirements apply to
the entire foundation. Similarly, if the mitigation falls under Substantial Improvement/Damage
requirements, the material requirements apply to all areas of the building that remains below the
minimum elevation specified by ASCE 24 (Table 2-2 of this document).
2.1.5 Utilities
ASCE 24-05 Section 7 includes requirements for electrical service; plumbing systems;
mechanical systems; heating, ventilation, and air-conditioning systems; and elevators. According
to ASCE 24, to avoid flood damage, utilities and attendant equipment in SFHAs must be
elevated above the minimum elevations in Table 2-3, and must be anchored to resist damage
from high wind. ASCE 24-05 Section 7 provides specific utility requirements and allows some
utility connections to be below the DFE, including some buried systems and connections
extending from the ground upwards. These portions of utilities must be designed, constructed,
and installed to prevent the entry of floodwater into the system or its components.
Additionally, utility systems and components can be protected by enclosing the systems within
structures that are dry floodproofed per the guidance in ASCE 24-05 Section 6.
Structure
Flood Hazard Areas
Category1
I DFE
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
1. See Table 1-3 in this document for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
Source: ASCE 24-05, Table 7-1
The ASCE 24 guidance requires that utilities be elevated to a greater height than specified by the
NFIP.
In accordance with ASCE 24, structures within a Zone V or Coastal A Zone may only be
elevated on open foundations consisting of piers, posts or columns, or piles (Figure 2-5).
Figure 2-5. Foundation requirements in Coastal High Hazard Areas and Coastal A Zones (Source: FEMA 2012c)
Unlike the NFIP, which does not differentiate between Zone A and Coastal A Zone design and
construction requirements, ASCE 24 prohibits elevation structurally supported by or on fill and
elevation on continuous foundation walls in Coastal A Zones. ASCE 24 allows for the placement
of nonstructural fill under and around a structure for dune construction or reconstruction if the
fill will not result in wave runup, ramping, or deflection of floodwaters that cause damage to
structures.
Table 2-4. Minimum Elevation of Bottom of Lowest Supporting Horizontal Structural Member of Lowest
Floor Relative to BFE or DFECoastal High Hazard Areas and Coastal A Zones
Figure 2-6. Lowest floor elevation requirements for Coastal High Hazard Areas (Zone V) and Coastal A Zones (Source: FEMA 2012c) Foundation Design Requirements
In accordance with the requirements in ASCE 24, foundations must be designed to minimize
forces acting on that system, and must be free of obstructions that will either transfer flood forces
to the structure or restrict the free passage of flood waters and waves during design flood
conditions. Buildings in Coastal High Hazard Areas and Coastal A Zones must be elevated on
and anchored to piles, columns, or, where permitted, walls serving as shear walls. Shear walls are
not continuous foundation walls around the perimeter of a structure. Permitted shear walls must
be oriented parallel to the direction of wave approach, and must be staggered so as not to form a
continuous wall or enclosed area. Foundations must be designed and constructed to withstand
design loads and load combinations, including the effects of erosion, scour, wind, waves,
currents, and flood-borne debris. The resistance of existing foundations to design loads and
conditions must be evaluated or meet the deemed-to-comply approach (see Appendix A). Fill
must not be used for structural support. Minor quantities of nonstructural fill for landscaping and
site drainage purposes are permitted.
In structure elevation projects where portions of the existing foundation will be used, loads and
conditions must be applied to the foundation (existing and new portions). This would include any
loads placed directly on the foundation as well as loads transferred to the foundation from the
superstructure, such as uplift from wind. The entire foundation, both new and existing, must
comply with ASCE 24 loading requirements and beams must be designed to create a load path
between the existing structure and the new elements.
In structure elevation projects where the existing foundation will be removed and replaced with a
new foundation, the provisions in ASCE 24 apply only to the foundation. The superstructure is
not subject to the provisions of ASCE 24.
2.2.1.1 Piles
ASCE 24-05 specifies that all foundations on erodible soils must be constructed on pile
foundations unless doing so is not feasible, in which case the provisions in Section 4.5.1 must be
met. Detailed design guidance is provided in ASCE 24-05 Sections 4.5.5 and 4.5.6 for elevating
a structure in a Coastal High Hazard Area or Coastal A Zone on piles.
DFE must be designed and constructed such that under base flood or lesser flood conditions, they
will collapse in such a way that (1) allows the free passage of floodwaters and (2) does not
damage the structure, supporting foundation system, or adjacent structures.
There are no restrictions on the size of the enclosure area; however, designers should be aware
that the presence and size of an enclosed area may affect flood insurance premiums. Specifically,
flood premiums in Zone V will increase significantly if a compliant breakaway enclosure is
constructed (the building will be rated as with obstruction); even higher premiums will be
assessed for Zone V structures with enclosed areas that are 300 square feet or more in size
(including stairwells and elevator enclosures), even if enclosed by compliant breakaway walls.
An insurance agent should be contacted to determine flood premiums for elevation projects that
include enclosures.
In accordance with ASCE 24, breakaway walls in Coastal A Zones must have openings to allow
for the automatic entry and exit of floodwaters during design flood conditions. Openings may be
engineered or non-engineered, but must prevent an imbalance of hydrostatic pressure (equivalent
to no more than 1 foot of variation in the water surface elevation inside and outside the enclosed
area). The design of the openings for breakaway walls in Coastal A Zones must follow the
requirements in ASCE 24-05 Section 4.6.2. FEMA TB-5, Free-of-Obstruction Requirements
(2008b), and FEMA TB-9, Design and Construction Guidance for Breakaway Walls Below
Elevated Coastal Buildings (2008a), offer related guidance regarding enclosures below the DFE.
2.2.4 Utilities
ASCE 24-05 Section 7 includes requirements for electrical service; plumbing systems;
mechanical systems; heating, ventilation, and air-conditioning systems; and elevators. To avoid
flood damage, utilities and attendant equipment in Coastal High Hazard Areas and Coastal A
Zones must be elevated above the minimum elevations in Table 2-6 and must be anchored to
resist damage from high wind. The minimum elevations specified in ASCE 24 for utility
elevation are higher than those required by the NFIP. In addition to the above-mentioned
requirements, in Coastal High Hazard Areas and Coastal A Zones, ASCE 24 requires that utilities
be capable of resisting anticipated flood loads, wave loads, and erosion and scour expected in
design flood conditions.
ASCE 24-05 Section 7 provides specific utility requirements and allows some utility connections
to be below the DFE, including connections extending from the ground upwards. These portions
of utilities must be designed, constructed, and installed to prevent the entry of floodwater into the
system or its components. ASCE 24-05 Section 7 includes requirements for electrical service;
plumbing systems; mechanical systems; heating, ventilation, and air-conditioning systems; and
elevators.
Table 2-6. Minimum Elevation of Utilities and Attendant Equipment Relative to BFE or DFE in Coastal
High Hazard Areas and Coastal A Zones
They are considered 2-4 Family if they contain 2 to 4 residential units and
incidental occupancies are limited to less than 25 percent of floor space.
They are considered other residential if incidental uses are limited to less than 25
percent of total floor space and there are at least 4 apartment units.
They are considered non-residential if they have some apartment units and 25 percent
or more of floor space is dedicated to incidental use.
The building type may restrict the potential mitigation options as HMA grant
programs do not fund dry floodproofing for residential buildings.
Historic Residential Buildings: For historic residential buildings that are not currently
occupied and will not be occupied in a residential capacity, an attempt should be made to
adhere to the provisions of ASCE 24 as closely as possible without compromising the
historic designation of the building. For historic residential buildings that are currently or
will be occupied in a residential capacity, ASCE 24 provisions for dry floodproofing
should be adhered to, including any requirements associated with adding a means of
egress from the dry floodproofed area. This is intended to improve protection to
residents. If strict adherence to ASCE 24s dry floodproofing provisions is too restrictive
to preserve the historic designation of a building, other mitigation measures should be
considered.
Table 3-1 provides a comparison of ASCE 24 and NFIP dry floodproofing requirements; the
latter can be found in FEMA TB-3, Non-Residential Floodproofing Requirements and
Certification for Buildings Located in Special Flood Hazard Areas (1993).
If the site and building use requirements are met, ASCE 24 stipulates the minimum
floodproofing elevation; however, more restrictive local floodplain ordinances may require
higher elevation criteria be met. Table 3-2 establishes the minimum lowest elevation of
floodproofing based on the structure category.
In addition to the minimum elevation of floodproofing, design process considerations should
include the duration of the flood, the rate of rise and fall of floodwaters, floodwater temperatures,
and potential flood-borne contaminants and debris. Flood velocities should be determined to
evaluate whether dry floodproofing is an appropriate mitigation approach and to evaluate site
conditions, such as the potential for soil and fill material to erode and scour. A site evaluation
may also dictate the values above the minimum requirements be selected for the flood-borne
debris calculations. In addition to meeting loading and siting requirements, the building elements
should be designed to meet the criteria described below in Sections 3.2 through 3.8.
NFIP/Technical
Dry Floodproofing ASCE 24
Bulletin 3
Zone A, Nonresidential buildings, P P
Nonresidential mixed use buildings**
Coastal High Hazard Area (Zone V, VE, or NP NP
V1V30), Floodway
Coastal A Zone NS NP
Areas where flood velocities are > 5 P NP
ft/second
Minimum elevation of floodproofing BFE (NFIP minimum) and BFE + 1 ft or 2 ft
BFE + 1 ft (Technical (depending on Structure
Bulletin 3)* Category) or DFE,
whichever is greater
Flood Emergency Operations Plan, R R
Inspection and Maintenance Plan, Warning
time, etc.
*Although the NFIP only requires floodproofing to base flood elevation (BFE), the Floodproofing Certificate shown in Technical
Bulletin 3 notes that 1 foot of freeboard above the BFE as a minimum elevation is required to satisfy flood insurance requirements.
Failure to include the 1 foot of freeboard will result in significant increases in flood insurance premiums.
**See Section 3 Introduction for what classifies as nonresidential mixed use.
BFE = base flood elevation NS = Not Specified
DFE = design flood elevation P = Permitted
ft = feet R = Required
NP = Not Permitted
Structure
Minimum Elevation of Lowest Floor
Category1
I BFE + 1 ft or DFE, whichever is higher
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
Source: ASCE 24, Table 6-1
1. See Table 1-3 for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
3.2 Foundation
The foundation for a retrofitted building must be assessed to determine whether it is capable of
resisting the additional loads that will be imposed by dry floodproofing the building. The
evaluation of the foundation must consider the building load path. Building components,
included into the dry floodproofing measures and load path must be able to resist the loads
outlined in Section 1.6 of ASCE 24-05. Flood loads include, but arent limited to, hydrostatic
loads, such as buoyancy against the slab and lateral loads against the foundation and attached
walls, hydrodynamic loads, and debris impact loads. Wall-to-foundation connections and the
foundation-to-ground connections are common areas, which may require additional construction
detailing beyond what is normally shown on construction plans. In addition to resisting the
specified loads, foundation elements associated with the dry floodproofed area must also be
designed to be watertight below the floodproofed design elevation and deemed to be
substantially impermeable.
3.4 Utilities
Section 7 of ASCE 24-05 outlines the minimum requirements for utilities and attendant
equipment such as, but not limited to, electrical, plumbing, and mechanical (heating and air-
conditioning) systems, and elevators. Utility lines or systems within the floodproofed area will
be protected by the dry floodproofing, but utilities and sanitary systems outside of the
floodproofed area and within the SFHA must be elevated to the minimum elevation for utilities
and attendant equipment as shown in ASCE 24-05 Table 7-1 (Table 2-3 of this document). Utility
systems outside of the floodproofed area and below the minimum required elevation must be:
Designed to resist all flood loads;
Constructed of flood damage-resistant materials;
Designed to minimize flood damage;
Impermeable to floodwaters; and
Able to resist the intrusion from floodwaters during an event.
With respect to a sanitary system, verifying that the existing system will not leak into
floodwaters or experience damage during a flood event is important. If there is potential for the
sanitary system to leak or become damaged during a flood event, it must be modified to avoid
these issues. More information on minimum requirements can be found in 44 CFR Section 60.3,
and design information can be found in FEMA 348, Protecting Utilities from Flood Damage
(1999).
3.5 Materials
Section 5 of ASCE 24-05 defines the material considerations for a dry floodproofing project. All
materials considered to be flood damage-resistant, must have sufficient strength, rigidity, and
durability to adequately resist flood-related and other loads. Although not explicitly defined in
the section, materials generally fall into two categories: those that are directly exposed to
floodwaters and those that are exposed to windblown rain and salt spray. Directly exposed
materials must be resistant to direct contact with the floodwaters and potential flood-borne
contaminants. All the materials, both those with direct exposure and those that will be protected,
must be resistant to moisture from precipitation and wind-driven water.
These requirements focus on metal components such as fasteners, angles, and straps. Because
concrete is a primary construction material for foundations and many nonresidential wall
systems, the mix must be designed for the corrosivity associated with a coastal environment.
Requirements for concrete cover over reinforcing steel must also be observed for any concrete
building elements. Wood and timber elements must be designed using the National Design
Specification for Wood Construction (ANSI/AF&PA 2005) and must be decay-resistant or
pressure treated with a preservative to resist deterioration and decay due to insects, fungi, and
flood-borne organisms. Interior finishes must also meet the requirements of a flood damage-
resistant material.
pump, and the sump pump system must be sized and designed to address leakage. Sump pumps
also require a backup source of electricity to ensure continued operation during a power outage,
per TB-3, Non-Residential Floodproofing Requirements and Certification for Buildings
Located in Special Flood Hazard Areas (1993). Additional guidance on the design of sump
pumps and internal drainage systems can be found in FEMA P-936, Floodproofing Non-
Residential Structures (2012b), and FEMA P-259, Engineering Principles and Practices for
Retrofitting Flood-Prone Residential Structures (2012a).
3.7 Egress
ASCE 24 requires that one door or primary exit be located above the minimum lowest elevation
of floodproofing and connected to the dry floodproofed areas. This is intended as an emergency
provision and not to encourage occupants to stay in the building during a flood event. Although
this may require retrofitting interior partitions or creating an opening in an exterior wall, this
should not result in a significant alteration for most nonresidential buildings. This provision may
be difficult to meet for some historic buildings without potentially compromising the historic
designation of the building. However, significant precautions should be taken to ensure that all
occupants are out of the building well before the arrival of floodwaters.
Structure
Category1 Minimum Elevation of Lowest Floor
I DFE
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
Source: ASCE 24-05, Table 2-1.
1. See Section 1, Table 1-3 in this document for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
4.1.3.1 Slab-on-Grade
If the mitigation reconstruction project is designed with a slab-on-grade foundation, the slab
must be installed on structural fill or undisturbed soil with adequate bearing capacity, as
specified in Section 2.4 of ASCE 24-05. The design and construction of the fill must account for
consolidation of the underlying soil, differential settlement, and slope stability and erosion
control. ASCE 24 includes specific guidance for compaction and side slopes. The top of the slab
must be at or above the elevation shown in Table 4-1 of this document. Reinforcement must be
used to prevent failure of the slab during design conditions, even if the slab is undermined by
erosion. The slab-on-grade foundation installed on structural fill must be placed so that there is
no loss of supporting soil during the design flood conditions.
Structure
Minimum Elevation of Lowest Floor
Category1
I DFE
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
Source: ASCE 24-05, Table 5-1
1. See Section 1, Table 1-3 in this document for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
4.1.6 Utilities
ASCE 24 requires that utilities and attendant equipment be elevated to or above elevations
provided in Section 7 of the standard, unless the utility is designed, constructed, and installed to
prevent floodwaters, including any backflow through the system, from entering or accumulating
within the components. Electrical services; plumbing systems; mechanical, heating, ventilation,
and air-conditioning systems; and elevators must be taken under consideration when meeting the
utility requirements of ASCE 24. Utility elevation requirements are provided in the Table 4-3.
Structure
Minimum Elevation of Lowest Floor
Category1
I DFE
II BFE + 1 ft or DFE, whichever is higher
III BFE + 1 ft or DFE, whichever is higher
IV BFE + 2 ft or DFE, whichever is higher
Source: ASCE 24-05, Table 7-1
1. See Section 1, Table 1-3 in this document for structure category descriptions.
BFE = base flood elevation
DFE = design flood elevation
ft = feet
4.2.3.1 Piles
Sections 4.5.5 and 4.5.6 of ASCE 24-05 detail considerations and design requirements for pile
foundation systems. All foundation systems constructed in erodible soils must be founded on
piles.
4.2.6 Utilities
ASCE 24 requires that utilities and attendant equipment be elevated to or above the elevation
stipulated for the bottom of the lowest supporting horizontal structural member of the lowest
floor unless the utility is designed, constructed, and installed to prevent floodwaters, including
any backflow through the system, from entering or accumulating within the components.
Electrical services; plumbing systems; mechanical, heating, ventilation, and air-conditioning
systems; and elevators must be taken into consideration when meeting the utility requirements of
ASCE 24. Utility DFEs for Coastal A Zones are provided in Table 4-6. Utility elevations are
subject to the orientation of the lowest horizontal structural member of the lowest floor relative
to the direction of the wave approach.
6 Historic Properties
A historic property is a resource (i.e., building, structure, site, object, or district) that is listed in
or eligible for listing in the National Register of Historic Places (NRHP) or listed on a State or
local inventory of historic places. The application of ASCE 24 to mitigation projects involving
historic properties is strongly encouraged to the extent practicablemeaning capable of being
done within existing constraintswithout compromising the qualities and characteristics that
make the resource eligible for listing in the NRHP or similar State and local inventories, also
referred to as historic integrity. While FEMA encourages the retention of historic integrity, it is
not a requirement that must be met to receive assistance under the HMA grant programs. In some
instances, proceeding with a mitigation project that causes a loss of historic integrity, but
provides a higher level of protection for the resource, may be more beneficial than maintaining
its historic integrity and providing a lower level of protection. If the former course is taken, the
requirements of ASCE 24 apply as outlined elsewhere in this document. If a mitigation project
results in the loss of historic integrity, FEMA will coordinate and consult with the applicant,
subapplicant, State Historic Preservation Office (SHPO), and any other interested parties, which
could include local, State, and/or national historic preservation organizations, to design an
appropriate course of action to resolve the adverse effect. Interested parties will be identified in
relation to the scale of the project and the scope of Federal involvement.
characteristics of a historic property that qualify the property for inclusion in the NRHP in a
manner that would diminish the integrity of the propertys location, design, setting, materials,
workmanships, feeling, or association. Adverse effects may include reasonably foreseeable
effects caused by the undertaking that may occur later in time, be farther removed in distance, or
be cumulative. If adverse effects will result, FEMA, in cooperation with the Applicant and
subapplicant, consults with the historic preservation stakeholders on ways to avoid, minimize, or
mitigate (treat) adverse effects to historic properties. Completion of the historic preservation
review process for adverse effects to historic properties can take time and should be considered
in developing the scope of work.
The subapplicant should contact the SHPO, or the local government representative responsible
for managing historic properties, early in the development phase of the project to identify
historic properties and evaluate whether the proposed work has the potential to adversely affect
those properties. FEMA EHP coordination early in the development phase of the project is
encouraged to help establish whether the scope of work has the potential to adversely affect
historic properties. The subapplicant should develop the scope of work (preferred) to avoid or
minimize adverse effects on historic properties. However, in cases where adverse effects cannot
be minimized or avoided, project eligibility will be determined on a case-by-case basis as an
adverse effect does not automatically make a project ineligible for FEMA funding. In many
cases, an adverse effect is not avoidable and the historic preservation review process outlined
above will allow for treatment measures to be developed to resolve the adverse effect. These
treatment measures can include, but are not limited to, a written history of the neighborhood,
architectural and photographic documentation, an educational installation and/or historical
marker. Proper treatment measures will be determined among all consulting parties in a
Memorandum of Agreement that will outline the particular roles and responsibilities of each
party in resolving the adverse effect.
Often, the treatment measures developed to resolve an adverse effect can be very beneficial to
the community. One such example involves the town of Belle Haven, NC, where repetitive
flooding became an issue for many of the towns properties located in an NRHP-listed historic
district. Rather than relocating to higher ground or demolishing and rebuilding, 379 properties
were elevated in place. With assistance from the North Carolina SHPO, the community
developed plans for an elevation project that would best preserve the historic character of the
district. As part of the plan, guidance was drafted for preserving porches, railings, balusters, and
steps and for replacing old materials with appropriate new materials where necessary. Although
the initial elevation of the buildings resulted in an adverse effect, many beneficial steps were
taken to minimize the effect and, as a result, Belhaven Historic District was able to maintain its
NRHP status. As part of the treatment measures developed for this project, large-format archival
photographs were taken of each building that would be affected. Additional treatment measures
included a recording of oral histories; a compilation of written memories; a historical
documentary on video and for posting on the internet; the conservation of historic artifacts,
documents, home movies, and historical photographs as part of a documented archival
collection; and museum exhibits that document and explain the importance of local historic
events to regional and national history.
An experienced contractor or architect will be familiar with the aspects of a historic building that
are important to retain, and will have ideas for approaches to mitigation while preserving the
historic character of the property and adjacent historic district (if applicable). Figure 6-1 shows
an example of a historic building that was elevated.
Section 2 of this document describes how to apply ASCE 24 requirements to elevation projects.
These requirements should be applied to the extent practicable for historic properties.
Figure 6-2. The entrance of the historic building leads into a tiled vestibule with a stairway leading to the elevated first
floor retail space. Before a flood event, the owners remove display items in the vestibule and slide a flood shield into
place protecting the elevated area from floodwaters. All building materials in the vestibule are flood damage-resistant.
(Darlington, WI)
Section 3 in this document describes ASCE 24 applicability to dry floodproofing projects. These
requirements should be applied to the extent practicable for historic properties.
community places conditions on the variance such that the historic structure must comply with
the floodplain management requirements in the State or communitys floodplain management
regulations, ICC will be available if the structure is declared Substantially Damaged or
repetitively damaged.
See FEMA P-467-2, National Flood Insurance Program (NFIP) Floodplain Management
Bulletin, Historic Structures (2008c), for a more complete explanation of how the NFIP treats
historic structures and suggested ways of minimizing flood damages to historic structures.
traditional building materials, such as wood, brick, stone, clay tile, slate, glass, and
plaster may cost more to purchase and may require more special expertise to install than
the readily available and cheaper synthetic alternatives (e.g., vinyl, aluminum, oriented
strand board, asphalt, concrete, drywall, laminate).
the application period is open, the State notifies the local governments of the availability of
assistance and relays information on the application process, project requirements, and eligibility
criteria for the local government. Table 7-1 shows the cost-share requirements for each program.
Property owners should work with their local government to express their interest in
participating in a flood mitigation project; the local government can then submit a subapplication
to the State and request HMA assistance. In general, the community applying for the grant must
be participating in the NFIP. Table 7-2 shows the eligible subapplicants for each program.
Figure 7-1. HMA grants cycle process showing roles and responsibilities of each stakeholder
applicable version of the HMA Unified Guidance for information on aggregating projects in an
application.
Key project elements necessary for flood mitigation applications include:
Identify the property (address, age, first floor elevation, flood hazard, and other
characteristics) to be mitigated.
Identify key project personnel and roles, such as design professional and contractor.
Select an eligible project (see Appendix C, Methodology for Evaluating Risks).
Ensure the project is consistent with the Mitigation Plan.
Have a professional inspect the structure to verify that the project can be implemented (if
possible; if not done at this stage, it must be done during Stage 4, Project
Implementation). See Initial Inspection and Data Collection Worksheet from Appendix
D, Checklists for Mitigation Projects.
Include design parameters illustrating that ASCE 24 requirements will be incorporated
into the project design or provide an affirmative certification statement. An example of an
acceptable affirmative certification statement is:
The Applicant affirms that the proposed scope of work will be implemented in
conformance with the design criteria outlined in the ASCE 24-05, Flood
Resistant Design and Construction, standard if this application is approved for
HMA.
The Applicant understands that prior to project closeout, verification and
design documentation and/or certification must be submitted to FEMA to
demonstrate that conformance with accepted engineering practices,
established codes, standards, modeling techniques, or best practices, including
adherence to ASCE 24-05 minimum design and construction requirements has
been met.
The Applicant understands that failure to implement this project, if approved,
in conformance with ASCE 24-05 will constitute a breach of the terms and
conditions of the Grant Award Agreement and may result in a recoupment of
Federal assistance.
The last two statements are more likely to appear in the grant agreement;
however, to establish clear understanding of the grant requirements, ideally they
will be included in the application as well.
Develop a project cost estimate and work schedule (see Develop Cost Estimate from
Appendix D).
Conduct a BCA using FEMAs BCA software (refer to Section 7.2 and Appendix B,
Benefit-Cost Considerations); if the benefit-cost ratio (BCR) is 1.0 or more, the project
is cost effective. FEMA requires a BCR of 1.0 or greater for funding (see BCA Input
Resources from Appendix D).
Ensure that properties located in designated SFHAs will obtain and maintain flood
insurance and that this condition will be recorded on the property deed.
Identify the appropriate agency consultation letters and responses (may include
correspondence from SHPO, U.S. Army Corps of Engineers, Natural Resources
Conservation Service, floodplain administrators, State coastal management agencies,
State environmental quality departments, State wildlife departments, and U.S. Fish and
Wildlife Service, etc.).
Include a signed environmental justice statement.
The local government submits the subapplication to the State (see Application Development
Resources in Appendix D for additional resources and information). The State then reviews the
projects, selects projects based on the States priorities, coordinates and resolves issues with the
subapplicants project application before submitting applications to FEMA for review. FEMA
reviews the projects for eligibility, completeness, engineering feasibility, cost effectiveness, and
EHP documentation. The review process helps to determine whether the Applicant and
subapplicant have demonstrated that all hazard mitigation activities are in compliance with all
relevant statutes, regulations, and program requirements, including other applicable Federal,
State, Indian Tribal, and local laws, implementing regulations, and Executive Orders (EOs),
which are detailed in the most applicable version of the HMA Unified Guidance. Once FEMA
approves and awards the project, the grant funds are distributed by the State to the local
governments, who will distribute it to individuals, as appropriate. No construction activities
should begin until after the money has been awarded because HMA assistance is not available
for activities initiated or completed prior to award or final approval.
called a period of performance, which is usually not more than 36 months. The homeowner or
local government should secure the professional services of a contractor or an engineer at this
stage to develop a detailed construction plan. If the scope of work or cost estimate changes as a
result, consult the most applicable version of the HMA Unified Guidance for direction on how to
revise the scope of work prior to construction.
During the period of performance, the local government must maintain a record of work and
expenditures for the quarterly reports that the State submits to FEMA. The basic steps for
implementing an HMA mitigation flood retrofit project are as follows:
1. Have a professional inspect the structure to verify that the project can be implemented
(unless already completed during Stage 3, Application Development). See Initial
Inspection and Data Collection Worksheet from Appendix D.
2. Finalize selection of viable project (unless already completed during Stage 3, Application
Development).
3. Secure professional services to complete the approved project. See Design Checklists
from Appendix D for important design considerations for the design professional.
4. Complete installation of the approved hazard mitigation. See Pre-Construction and Walk-
Through Checklist and Construction Checklist and Compliance Checks from Appendix D
for inspection items and compliance checks that should occur prior to and during
construction.
5. Inspect the completed hazard mitigation elements and verify other program requirements.
See Final Walk-Through Checklist and Punch-List Items from Appendix D.
compliance with the scope of work. In addition, the Grantee may conduct a final site visit prior
to project closeout. Supporting documentation that is needed from the subgrantee includes but is
not limited to copies of all applicable permits and inspections, documented expenditures
consistent with the approved SF-424, Application for Federal Assistance, FEMA Form 20-18,
Report on Government Property, cost-share records including cash and in-kind services provided
by the community, and latitude/longitude coordinates for each mitigated structure with an
accuracy of +/- 20 meters. Complete grant closeout records must be on file for at least 3 years
from the submission date of the last expenditure report.
Although closeout requirements typically apply to all three project types addressed in this
guidance, some are unique to specific mitigation projects as shown in Table 7-3. Additionally, the
most applicable version of the HMA Unified Guidance should be referenced to ensure all
closeout requirements are addressed.
Table 7-3. Closeout Requirements Unique to Elevation, Mitigation Reconstruction, and Dry Floodproofing
project will be cost effective. If the project has marginal increases in cost, the impact to the BCR,
or cost effectiveness of the project, will be negligible. Often times, increases in project costs
result in a reduction of flood risk (i.e., elevating a home 2 feet above the BFE instead of just to
the BFE).
The FEMA BCA Tool is used to determine the cost effectiveness of proposed mitigation projects
submitted for assistance under FEMAs HMA grant programs. FEMA developed the software to
assist in complying with the most applicable version of the HMA Unified Guidance and Stafford
Act requirements, which state that FEMA can only support cost-effective mitigation activities.
The software is used to estimate the magnitude of potential loss caused by a natural disaster
(flood, hurricane, tornado, earthquake, or wildfire) with and without the proposed mitigation. For
flood events, loss is estimated using depth-damage functions, which are used to predict
inundation impacts to the building, contents, and use of the building. Depth-damage functions
relate flood depths to predicted percentages of damage to a building.
The probability of loss is based on the flood recurrence interval, which is typically based on
flood hazard data from a FEMA Flood Insurance Study and/or hydrologic and hydraulic study.
When flood hazard data are either unavailable or limited, the recurrence interval may need to be
based on the Unknown Frequency Calculator, which is built into the Damage Frequency
Assessment module of the FEMA BCA Tool.
Projects that are eligible for funding under the HMA programs must be cost effective, i.e., have a
BCR equal to or greater than 1.0. A FEMA memorandum, released on August 15th, 2013,
provides a methodology to streamline the benefit cost analysis for certain mitigation project
types. This methodology was based on FEMAs Risk Reduction Division analysis of 11,000
acquisition and elevation projects. FEMA has determined that the average benefits for each type
of project are $276,000 and $175,000, respectively (2013 dollars). Therefore, FEMA has
determined that the acquisition or elevation of a structure located in a 100-year floodplain (as
delineated on the FIRM or based on best available data) that costs less than or equal to the
average benefit listed above is considered cost effective. For projects that contain multiple
structures, the average cost of all structures in the project must meet the stated criterion. There is
no need for applicants to conduct a separate BCA for a structure that meets this criterion.
For structures identified in a riverine SFHA on the current effective FIRM and declared
Substantially Damaged as a result of the impacts of flooding by a local authority having such
jurisdiction, property acquisition and structure demolition or relocation are considered cost
effective and a BCA is not required to be submitted for the structure.
For more information about conducting a BCA for elevation, dry floodproofing, and mitigation
reconstruction projects, refer to Appendix B.
to the National Historic Preservation Act, addressed in Section 6 of this document, these include,
but are not limited to:
The National Environmental Policy Act (NEPA)
The Endangered Species Act
The Clean Air Act
The Clean Water Act
EO 11988 (Floodplain Management)
EO 11990 (Protection of Wetlands)
EO 12898 (Environmental Justice)
The HMA grant program includes an EHP review process that addresses potential impacts of
mitigation projects on environmental resources.
Three primary categories of flood mitigation are addressed by ASCE 24: building elevation, dry
floodproofing, and mitigation reconstruction. The following sections describe the potential for
environmental impacts associated with each of these types of mitigation.
7.3.1.1 Viewsheds
If done properly, taking into consideration its surroundings, elevation can be done without
adversely affecting the aesthetic character of the community. Aspects of the project design that
must be carefully considered to avoid aesthetic impacts are highlighted in Section 6.2.1 of this
document.
possible. If a critical facility must be located in a floodplain, it should be provided a higher level
of protection so that it can continue to function and provide services after a flood.
7.3.5 Executive Order 11990 Protection of Wetlands and the Clean Water Act
Actions that affect wetlands and other waters of the United States or navigable waters of the
United States require coordination with the U.S. Army Corps of Engineers to ensure compliance
with Section 404 of the Clean Water Act and Section 10 of the Rivers and Harbor Act. The
subgrantee is responsible for applying for and obtaining required Section 404 and Section 10
permits. Further, the subgrantee is responsible for obtaining a water quality certification from the
appropriate State agency for any project subject to Section 404 permitting.
The 2012 IRC, IBC, and IEBC describe various categories to classify work on existing buildings.
For flood mitigation projects on residential and nonresidential structures, alterations and repairs
are typically the most applicable categories. The 2012 IRC provides provisions for existing
residential buildings in Appendix J. The 2012 IBC covers provisions for existing nonresidential
buildings in Chapter 34. If adopted by the authority having jurisdiction, the 2012 IEBC provides
further, more detailed requirements and guidance for work on existing buildings (both residential
and nonresidential). With respect to alterations, various levels of alterations can be triggered;
higher levels correspond to greater amounts of work being done to the structure. In some cases,
these provisions can trigger additional work that may need to be done to the structure or portions
of the structure to meet certain building code requirements. State-specific codes and older codes
may have different requirements; therefore, the provisions of the applicable building code should
be carefully checked before the project is implemented.
Additional information on these provisions, and the type of work they can apply to, can be found
in FEMA 499, Home Builders Guide to Coastal Construction, Technical Fact Sheet No. 9.1.
(2010b).
Any owner or authorized agent who intends to construct, enlarge, alter, repair,
move, demolish, or change the occupancy of a building or structure, or to erect,
install, enlarge, alter, repair, remove, convert or replace any electrical, gas,
mechanical or plumbing system, the installation of which is regulated by this
code, or to cause any such work to be done, shall first make application to the
building official and obtain the required permit.
The requirement for a permit in both the building code and NFIP regulations means that owners,
contractors, design professionals, and officials must be aware of both requirements. Although the
model International Codes contain the NFIP provisions, many communities use a separate local
ordinance for their floodplain development regulations and multiple permits may be required
depending on the communitys enforcement of one or more requirements. For example, a
building official may require a permit for construction of a residential building per IRC
requirements. However if that building is located in a floodplain, the floodplain administrator
may also require a permit for construction in an SFHA per the NFIP. In some cases, these roles
(building official and floodplain administrator) may be given to one official, but in other cases
there may be multiple officials with varying requirements. The design professional must be
aware of the requirements that apply to a specific site so that the most restrictive applicable
requirements are met.
The 2012 IBC requires buildings constructed in flood hazard areas to be in accordance with
ASCE 24 (see Section 1612.4 of the 2012 IBC), while the 2012 IRC references ASCE 24 only
for buildings and structures constructed in floodways (see Section R322.1 of the 2012 IRC).
Although communities that do not have an effective building code but participate in the NFIP do
not have to obtain a permit for construction and development per the building code, they must
still obtain a permit if they are developing or constructing in an SFHA, per NFIP requirements.
Communities with no building code may have local ordinances that also require a permit and
provide more restrictive requirements than the minimum NFIP requirements. Without a building
code, the authority having jurisdiction may have difficulty enforcing the provisions of ASCE 24,
as they will be less familiar with those requirements. A floodplain administrator may not have the
same level of building expertise that a building official would have, because their primary duties
typically deal with floodplain development rather than building design and construction. In such
cases, local floodplain administrators may need to rely on affidavits or certifications from
licensed professional designers to ensure compliance with ASCE 24.
Permitting provides an important form of oversight to ensure that buildings are being properly
designed and constructed, which becomes even more crucial when a building or structure is
located in an SFHA. Communities that do not participate in the NFIP cannot receive Federal
assistance for flood mitigation projects located in a floodplain.
Figure 7-2 illustrates the permitting process. Several steps must be taken before a building permit
can be issued. After a zoning review and verification that the application meets the NFIP and
local ordinances for development, an application should undergo a building code review.
Verification of Substantial Improvement, BFE and lowest floor elevation, and impacts on the
floodway should be considered. Once a building permit has been issued, the Applicant may begin
construction. The site should be inspected both during and after construction to verify that NFIP
regulations and local ordinance requirements have been followed. After final inspection, an
elevation certificate should be provided, and the final record should be logged with the authority
having jurisdiction.
A Deemed-to-Comply Table
Table A-1. Deemed-to-Comply Table
Section Title
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
1.0 General
New construction and substantial improvements shall meet the
This standard applies to new and substantially improved/damaged
requirements of ASCE 24-05. Mitigation reconstruction projects shall
1.1 Scope structures in flood hazard areas that are subject to building code
meet the requirements of ASCE 24-05. For all other projects, ASCE 24-
requirements
05 shall apply only to the mitigated portions of those projects.
This standard applies to the larger of: 1) Special Flood Hazard Area
Identification of Flood
1.3 (SFHA) and 2) lands designated by the authority having jurisdiction Must comply with ASCE 24-05 requirements.
Hazard Areas
(AHJ) as flood hazard areas.
Determine whether an existing structure lies in whole or in part in flood
hazard area; if so, this standard will apply as indicated throughout this
Determine whether a structure lies in whole or in part in flood hazard
Identification of summary. Structures shall be classified by ASCE 24-05 Table 1-1, and
1.4 area; classify structures; don't allow new structures to damage or
Floodprone Structures applicable provisions shall be applied. Mitigation projects shall not
compromise flood protective works (1.4.2).
damage, endanger, or harm protective works, or interfere with
maintenance and repairs of such works.
Basic Design and Designed, constructed, connected, and anchored to resist flotation
1.5 Construction collapse or permanent lateral movement during design loads and load Must comply with ASCE 24-05 requirements.
Requirements combinations.
Design loads and load combinations for mitigated structural elements
Loads in Flood Hazard shall be in accordance with the applicable building code requirements or
1.6 Loads and load combinations shall be in accordance with ASCE 7-02.
Areas the requirements as shown in ASCE 24-05, whichever is more stringent,
or the latest version of ASCE 7 if no building code is in effect.
Section Title
Basic Requirements
for Flood Hazard
Areas not Identified Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
2.0
as Coastal High
Hazard Areas or
Coastal A Zones
This section provides requirements for new construction
2.1 Scope and substantial improvements in A zones (not including Section 2 shall apply to the mitigated portions of an existing structure.
Coastal A Zone).
Structures and fill shall not be placed in floodways unless it
Development in can be demonstrated that the flood level will not be
2.2 Section 2.2 shall apply only to mitigation projects allowed within the floodway.
Floodways increased and the conveyance will not be reduced more
than the allowable amounts.
Table 2-1: Design flood elevation (DFE) or base flood Mitigated structures shall be elevated to the elevation specified in ASCE 24-05
2.3 Elevation Requirements
elevation (BFE) + freeboard, whichever is higher. Table 2-1.
Placement of structural fill shall account for consolidation and settlement of
underlying soil due to weight of fill and structure. Fill shall be placed in lifts and
compacted. Fill shall be stable and protected from scour and erosion, if
Placement of structural fill shall account for consolidation needed.
and settlement of underlying soil due to weight of fill and
2.4 Use of Fill structure. Fill shall be placed in lifts and compacted. Fill With respect to undisturbed areas, field observations and testing shall be
shall be stable and protected from scour and erosion, if permitted to be used to evaluate compliance with this requirement, provided
needed. such efforts ascertain whether settlement has occurred or is occurring, whether
settlement has caused or is likely to cause structural problems, and whether
proposed mitigation measures are likely to cause or exacerbate settlement to
the point where the mitigated structure will sustain structural damage.
Slabs shall be placed on structural fill or undisturbed soil
with adequate bearing capacity. Top of slab shall be at or
above elevation per Table 2-1. Bottom of turned down Slabs, footings, and underlying soil shall support the structure during design
footings of slabs shall be below the depth of expected flood conditions such that the structure is not subject to flotation collapse or
Slabs-on-Grade and scour. Slabs shall be reinforced to prevent breakup if lateral movement. Existing slabs, footings, and underlying soil shall be
2.5
Footings undermined. Slabs on structural fill shall suffer no loss of evaluated using field observations and testing to a reasonable standard of care
supporting soil during design flood. Footings shall support to verify that during design flood conditions they will not lead to structure
the structure (and prevent flotation, collapse, lateral floatation, collapse, or lateral movement.
movement) during design flood conditions. Slabs under
elevated buildings shall not have turned down edges.
Section Title
Basic Requirements
for Flood Hazard
Areas not Identified Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
2.0
as Coastal High
Hazard Areas or
Coastal A Zones
Enclosed areas below the DFE shall be used solely for
parking, building access, or storage. Walls of enclosed
Enclosures Below the areas, including breakaway walls, shall be equipped with
2.6 Must comply with ASCE 24-05 requirements.
DFE openings to provide for automatic entry and exit of
floodwaters. Openings shall meet the non-engineered or
engineered opening requirements.
Section Title
High Risk Flood Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
3.0
Hazard Areas
Section 3 shall apply to new construction and substantial Section 3 applies to new construction and substantial improvement/substantial
3.1 Scope
improvements in high risk flood hazard areas. damage unless a waiver is granted by FIMA.
Structures shall not be allowed in alluvial fan areas unless a
whole fan flood damage reduction project exists, and such
project has an operations and maintenance plan. Structures
shall not be constructed at the apex of the fan or in the fan's
The ASCE 24-05 provision applies to new construction and substantial
3.2 Alluvial Fan Areas meandering flow paths. Where permitted: 1) structures shall
improvement/substantial damage unless a waiver is granted by FIMA.
have the lowest floor at least 1.0 foot above the highest
adjacent grade (higher, if required by the community), 2)
foundations shall be designed to resist scour and flood loads
for design flow velocities, or 5 feet/second, whichever is higher.
Section Title
High Risk Flood Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
3.0
Hazard Areas
Structures shall not be constructed in areas subject to high
velocity flow unless protective works have been determined to
provide protection during a design flood event. Protective
works must have an operations and maintenance plan. High
The ASCE 24-05 provision applies to new construction and substantial
3.6 High Velocity Flow Areas velocity flow areas shall be determined by analysis and such
improvement/substantial damage unless a waiver is granted by FIMA.
analyses shall be documented in an engineering report.
Section 1.2 defines High Velocity Flow as flow velocity greater
than 10 feet/second adjacent to a structure or foundation
during a design flood or lesser conditions.
Structures constructed in Coastal High Hazard Areas and
Coastal A Zones shall meet the requirements of Section 4.
Areas Subject to Wave Structures shall not be constructed in other areas subject to
3.7 Must comply with ASCE 24-05 requirements.
Action high velocity wave action (defined in Sec. 1.2 as 3.0 feet wave
height or runup depth) unless they meet the requirements of
Section 4.
Structures shall not be constructed in areas subject to
transportation of damage-causing ice or debris unless
protective works have been determined to provide protection
The ASCE 24-05 provision applies to new construction and substantial
3.8 Ice Jam Debris Areas during a design flood event. Protective works must have an
improvement/substantial damage unless a waiver is granted by FIMA.
operations and maintenance plan. Ice jam and debris areas
shall be determined by analysis and such analyses shall be
documented in an engineering report.
Section Title
Coastal High Hazard
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
4.0 Areas and Coastal A
Zones
Section 4 shall apply to new construction and substantial improvements
in Coastal High Hazard Areas and Coastal A Zones. For the purposes of
this standard, Coastal High Hazard Area shall mean those locations
designated as V zones on the flood hazard map, or areas where 3 feet
4.1 Scope Section 4 shall apply to the mitigated portions of an existing structure.
wave heights or runup depths will occur during the base flood. For the
purposes of this standard, Coastal A Zone shall mean those locations
where the stillwater depth and wave conditions will yield a wave height
equal to or greater than 1.5 feet during the base flood.
Design shall account for lateral and vertical wave loads, other flood Design shall account for lateral and vertical wave loads, other flood
4.2 General
loads, and scour and erosion. loads, and scour and erosion.
Structures shall be sited landward of the reach of mean high tide and Mitigation projects shall not be allowed for or result in a building that is
shoreline construction setbacks, and shall not alter sand dunes or seaward of the reach of mean high tide. Mitigation projects shall not
4.3 Siting
mangrove stands if those alterations reduce the wave and flow cause the wave or flow dissipation characteristics of sand dunes or
dissipation characteristics. mangrove stands to be reduced.
The bottom of the lowest horizontal structural member of the lowest floor The bottom of the lowest horizontal structural member of the lowest floor
4.4 Elevation Requirements
shall be at or above the elevation specified in Table 4-1. shall be at or above the elevation specified in Table 4-1.
Structures shall be elevated on and anchored to piles, columns, or Structures shall be elevated on and anchored to piles, columns, or
where permitted, walls serving as shear walls. Foundations shall be free where permitted, walls serving as shear walls. Foundations shall be free
of obstructions. Permitted shear walls shall be oriented parallel to the of obstructions. Permitted shear walls shall be oriented parallel to the
direction of wave approach, and shall be staggered so as not to form a direction of wave approach, and shall be staggered so as not to form a
continuous wall or enclosed area. continuous wall or enclosed area.
Spread footing, mat, or raft foundations shall not be permitted unless the Spread footing, mat, or raft foundations shall not be permitted unless the
top is below the eroded ground elevation, or unless subsurface top is below the eroded ground elevation, or unless subsurface
Foundation nonerodible conditions prevent the use of deeply embedded piles or nonerodible conditions prevent the use of deeply embedded piles or
4.5
Requirements columns (footings, mats, and rafts shall be anchored to the nonerodible columns (footings, mats, and rafts shall be anchored to the nonerodible
strata). strata).
Foundations shall be designed and constructed to withstand design Foundations shall be designed and constructed to withstand design
loads and load combinations, including the effects of erosion and scour. loads and load combinations, including the effects of erosion and scour.
Fill shall not be used for structural support. Nonstructural fill for Fill shall not be used for structural support. Nonstructural fill for
landscaping and site drainage purposes shall be permitted. landscaping and site drainage purposes shall be permitted.
Grade beams shall be permitted but shall be designed to perform their Grade beams shall be permitted but shall be designed to perform their
intended function when undermined by scour and erosion. Bracing shall intended function when undermined by scour and erosion. Bracing shall
Guidance for Applying ASCE 24 Engineering Standards to
A-6 Flood Retrofitting and Reconstruction Projects
Deemed-to-Comply Table
A
Section Title
Coastal High Hazard
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
4.0 Areas and Coastal A
Zones
be designed to minimize flood loads. The structure shall be designed to be designed to minimize flood loads. The structure shall be designed to
withstand any flood loads transferred from grade beams and bracing. withstand any flood loads transferred from grade beams and bracing.
To the extent possible, designers should evaluate existing foundation
elements that will be part of the new, elevated foundation to determine
whether they can support the design loads as described in ASCE 24
and ASCE 7.
Enclosed areas shall be used solely for parking, building access, and Enclosed areas shall be used solely for parking, building access, and
storage. storage.
Enclosed Areas Below Walls of enclosures shall be designed and constructed to break away Walls of enclosures shall be designed and constructed to break away
4.6 without adversely affecting the main structure, and without producing without adversely affecting the main structure, and without producing
the DFE
debris capable of causing damage to structures. Enclosure walls in debris capable of causing damage to structures. Enclosure walls in
Coastal A Zones shall be equipped with openings that allow for the Coastal A Zones shall be equipped with openings that allow for the
automatic entry and exit of floodwaters. automatic entry and exit of floodwaters.
Mitigation projects shall not be permitted where an erosion control
Erosion control structures shall not be connected to the building
Erosion Control structure is connected to a building or its foundation, or where the
4.7 foundation or other parts of the building. Erosion control structures shall
Structures erosion control structure will cause damaging flow diversion, or wave
not focus or increase flood forces or erosion impacts on any structure.
runup or reflection, or erosion impacts to the building.
Decks, pads, and patios are permitted below the DFE provided they are
Decks, concrete pads, and patios will be retrofitted only if they pose a
structurally independent of the primary structure foundation, and do not
potential threat to the main structure or are attached to the structure.
Decks, Concrete Pads adversely affect adjacent structures through flow deflection or debris.
4.8 Efforts will be made to minimize the work necessary to retrofit these
and Patios Decks, pads, and patios shall be of breakaway construction, and shall
portions of the structure to make the deck, pad, or patio such that they
not produce damage-causing debris. Concrete pads shall have a
no longer pose a threat to the building.
maximum thickness of 4 inches and not be reinforced.
Section Title
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
5.0 Materials
New construction and substantial improvements shall be
constructed with flood-damage-resistant materials below the
Mitigated portions of an existing structure shall utilize flood-damage-resistant
elevation specified in Table 5-1. Unless designed to break
5.1 General materials below the elevation specified in Table 5-1, and shall use materials
away, materials shall have the strength, rigidity, and durability
capable of resisting damage, deterioration, corrosion, and decay.
to withstand floods and other loads. Materials shall be capable
of resisting damage, deterioration, corrosion, and decay.
Material specific specifications shall be in accordance with the applicable building
Specific Material ASCE 24-05 contains specific requirements or cites reference
code requirements or the requirements as shown in ASCE 24-05, whichever is
5.2 Requirements for Flood standards for: metal connectors and fasteners, structural steel,
more stringent, or the latest version of the specification if no building code is in
Hazard Areas concrete, masonry, wood and timber, and finishes.
effect.
Section Title
Dry and Wet Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
6.0
Floodproofing
Section 6 addresses floodproofing for new construction and
substantial improvements. Floodproofing shall take into
6.1 Scope consideration flood loads and load combinations, the nature of Section 6 shall apply to mitigation projects.
flood-related hazards, flood warning time and access, structure
occupancy and use, and functional dependence.
Dry floodproofing shall render a structure substantially
impermeable to the passage of floodwater below the elevation
specified in Table 6-1. Dry floodproofing shall be limited to non-
residential structures and non-residential portions of mixed-use
structures. Dry floodproofing shall be limited to structures
where flow velocities adjacent to the structure are less than or
equal to 5 feet/second. Where human intervention is
6.2 Dry Floodproofing Must comply with ASCE 24 requirements.
necessary, dry floodproofing shall be limited to situations
where at least 12 hours of flood warning time is provided, or
where a community warning and evacuation plan provides
sufficient time to activate/install the floodproofing and evacuate
floodproofing staff. Where removable shields are included in
the dry floodproofing, a flood emergency plan approved by the
AHJ is required.
Wet floodproofing shall be accomplished using flood-damage-
resistant materials and techniques. Wet floodproofing of
enclosed spaces below the elevation in Table 6-1 shall be
limited to Category 1 structures; enclosures used for parking
6.3 Wet Floodproofing Must comply with ASCE 24 requirements.
building access or storage in any category building; functionally
dependent structures; and agricultural buildings not classified
as Category 1, that cannot be located elsewhere, and that are
used solely for agricultural purposes.
Section Title
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
7.0 Utilities
Utilities and equipment shall not be permitted below the
elevations in Table 7-1, unless in dry-floodproofed spaces or
specifically permitted by this section, and unless designed, Section 7 shall apply to all building utilities and equipment that are replaced
constructed, and installed to prevent floodwaters from entering during a mitigation project. Provisions related to underground lines do not apply
or accumulating within the components. Utilities and equipment
7.1 General unless the underground lines are affected or disturbed during the construction of
shall be anchored to resist flood forces. Utilities and equipment
shall not be mounted on, or pass through, or be located along the mitigation project.
breakaway walls. Supports for elevated exterior platforms for
utilities and equipment shall be capable of resisting flood loads
including effects of erosion and scour.
If electrical service is below the minimum flood elevation, it
must be waterproof or conform to National Fire Protection
Section 7 shall apply to all building utilities and equipment that are replaced
Association (NFPA) 70, National Electrical Code. All electrical
during a mitigation project. Provisions related to underground lines do not apply
7.2 Electrical Service components below the minimum elevation must be designed to
unless the underground lines are affected or disturbed during the construction of
resist flood forces. Electrical components must be secured to
the mitigation project.
the structure and not a breakaway wall or enclosures.
Everything must be sealed to prevent water intrusion.
If plumbing equipment is below the minimum flood elevation, it
must be waterproof. All plumbing components below the
minimum elevation must be designed to resist flood forces.
Plumbing components must be secured to the structure and
not a breakaway wall or enclosures. Backflow devices are Section 7.2 shall apply to all building utilities and equipment that are replaced
required for lines that extend below the DFE. Everything must during a mitigation project. Backflow prevention valves should be installed for all
7.3 Plumbing Systems
be sealed to prevent floodwater intrusion or loss of sewage into mitigation projects and tanks should be properly anchored for all mitigation
floodwaters. Underground lines must be designed to address projects.
scour and erosion. Storage tanks must be anchored to resist
flood forces. Sanitary systems must be designed to operate
during flood conditions and subsequent days following the
flood event.
Section Title
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
7.0 Utilities
Mechanical systems should be located above the DFE, if any
is below the minimum flood elevation, it must be waterproofed.
All mechanical components below the minimum elevation must
Section 7 shall apply to all building utilities and equipment that are replaced
be designed to resist flood forces. Mechanical components
Mechanical, HVAC during a mitigation project. Provisions related to underground lines do not apply
7.4 must be secured to the structure, located on the landward side
Systems unless the underground lines are affected or disturbed during the construction of
of the structure, and not secured to breakaway walls or
the mitigation project.
enclosures. Everything must be sealed to prevent water
intrusion. Fuel lines must include an automatic float shutoff
valve when floodwaters rise above the supply line elevation.
All elevator components must be above the DFE. If anything is
located below that, it must be made of flood-damage-resistant
Section 7 shall apply to all building utilities and equipment that are replaced
materials and capable of resisting physical damages due to a
during a mitigation project. Provisions related to underground lines do not apply
7.5 Elevators flood. Electrical controls must be located above the DFE.
unless the underground lines are affected or disturbed during the construction of
Drainage must be detailed for elevator pits below the DFE. The
the mitigation project.
cab must be fitted such that it cannot descend below
floodwaters.
Section Title
Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
8.0 Building Access
Stairways and ramps located below the Minimum Lowest Floor
Elevation must be constructed of flood-damage-resistant
materials and be designed to resist flood-related loads and to
minimize the transfer of flood loads to the structure and
8.1 General Section 8 shall apply to mitigation projects.
structure foundation or to breakaway during design flood
conditions without causing damage to the structure, including
the foundation. Enclosures must comply with other enclosure
provisions in ASCE 24.
Section Title
Miscellaneous Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
9.0
Construction
Structures must comply with loads in Section 1.6 and be
elevated as per Section 2.3 and 4.4, using materials that Items not directly related to the mitigation project will not be required to meet the
9.1 General
conform to Section 5, and all associated utilities must conform ASCE 24-05 provisions requirements.
to Section 7.
In flood hazard areas other than Coastal High Hazard Areas,
Coastal A Zones, and other high risk flood hazard areas,
decks, porches, and patios that are structurally connected
must act as a continuation of the structure and meet loading
requirements, and those below the DFE must also meet the
opening requirements. Those not structurally connected to a
structure designed below the Minimum Lowest Floor Elevation
In some instances, decks, porches, and patios that cannot be successfully
shall conform to the foundation requirements of Section 1.5.3
retrofitted may need to be detached from the structure. The level of retrofitting
Decks, Porches and and enclosed walls shall conform to the requirements for
9.2 necessary will be to a threshold necessary to ensure that during a design flood
Patios openings as stated in Section 2.6. In V Zones and Coastal A
condition the deck, porch, or patio does not cause damage to the main structure
Zones (and other high risk flood areas), decks, porches, and
or its foundation.
patios that are structurally connected to the structure must act
as a continuation of the structure and be located above the
DFE. Those not structurally connected to a structure and below
the Minimum Lowest Horizontal Structural Member Elevation
shall be designed in accordance with Section 4.8 and enclosed
walls shall conform to the breakaway wall requirements in
Section 4.6.
In flood hazard areas other than Coastal High Hazard Areas,
Coastal A Zones, and other high risk flood hazard areas,
carports and garages that are structurally connected must act
as a continuation of the structure and meet loading
requirements, and those below the DFE must also meet the In some instances, garages and carports that cannot be successfully retrofitted
opening requirements and at least two sides must be above may need to be detached from the structure. The level of retrofitting necessary
9.3 Garages grade (floodproofing provisions apply to nonresidential will be to a threshold necessary to ensure that during a design flood condition the
structures). Those not structurally connected to a structure garage or carport does not cause damage to the main structure or its foundation.
designed below the DFE shall conform to the foundation
requirements of Section 1.5.3 and enclosed walls shall
conform to the requirements for openings as stated in Section
2.6. In V Zones and Coastal A Zones (and other high risk flood
areas), carports and garages that are structurally connected to
Guidance for Applying ASCE 24 Engineering Standards to
Flood Retrofitting and Reconstruction Projects A-13
Deemed-to-Comply Table
A
Section Title
Miscellaneous Summary of ASCE 24-05 Provision ASCE 24-05 Provision as applied to HMA
9.0
Construction
the structure must act as a continuation of the structure, those
areas below the DFE must be constructed with breakaway
walls in conformance to the requirements of Section 4, and all
sides must be above grade. Those not structurally connected
to a structure and below the DFE shall be designed in
accordance with Section 4 and enclosed walls shall conform to
the breakaway wall requirements in Section 4.6.
In flood hazard areas other than Coastal High Hazard Areas,
Coastal A Zones, and other high risk flood hazard areas,
All fireplace and chimney foundations will be retrofitted to resist flood loads and
chimneys that extend below the DFE must be designed to be
wind loads (and other loading), but where it is not possible to make the chimney
9.4 Chimneys and Fireplaces vertically supported and independent of the structure, and must
or fireplace structurally independent, it will be allowed to remain structurally
be designed to withstand all flood-related loads. In V Zones
attached.
and Coastal A Zones, they must be supported by an open
foundation designed to meet all loading requirements
Pools must resist all flood load requirements. If attached to the
structure, the pool must act as a continuation of the structure.
May cause significant cost increases for pools attached to the structure. These
In V Zones or Coastal A Zones, if the pool is attached to the
9.5 Pools are ineligible costs for a HMA project, so pool requirements are the responsibility
structure, it must be above the DFE and be elevated per
of the homeowner and must be funded by the homeowner.
Section 4.4 or be designed to break away during flooding
without producing damaging debris.
Tanks must be designed to be consistent with Section 7 and
be anchored to resist all flood loads. The tank must also be
May not impact many projects since this section refers to tanks independent of
9.6 Storage Tanks designed to prevent the release of its contents during a flood
the structure.
condition. It must be anchored to resist up to 1.5 times its
buoyancy load when empty during a design flood event.
B Benefit-Cost Considerations
B.1 Introduction
The purpose of this appendix is to provide basic guidance on using the Federal Emergency
Management (FEMA) Benefit-Cost Analysis (BCA) Tool (Version 4.5.5) (2009) to complete a
BCA for the three primary mitigation project types covered in this publication:
Structure elevation
Dry floodproofing
Mitigation reconstruction
B.2 Elevation
The Flood module in the BCA Tool is typically used to complete a BCA for an elevation project.
The Flood module relies on flood hazard data, building characteristics (size, occupancy type,
replacement value, etc.), depth-damage function (DDF), and the increase in building elevation to
estimate before- and after-mitigation damages. It is important to reflect the total elevation
amount in the BCA as well as the project cost. The elevation amount should be the increase in
building elevation necessary for the building to be at or above the design flood elevation (DFE).
The DFE is the regulatory flood elevation adopted by a local community or provided by ASCE
24, whichever is greater. Typically, the DFE is the base flood elevation (BFE) plus any freeboard
adopted by the community. The BFE is defined as the flood elevation, including wave height,
having a 1-percent chance of being equaled or exceeded in any given year and the minimum
elevation requirement under the National Flood Insurance Program (NFIP).
As a general rule of thumb, elevation projects for buildings situated at or below the 10-percent-
annual-chance flood elevation (or 10-year flood) are most likely cost effective, those below the
4-percent-annual-chance flood elevation (or 25-year flood) are likely cost effective, and those
above the 4-percent-annual-chance flood elevation are not likely cost effective.
In addition to traditional elevation projects where an entire building is elevated, the BCA Tool
can also be used to evaluate the cost effectiveness of elevating utilities or other critical
components of a building. Buildings that are already above the required DFE may have utilities
in locations such as a basement that are subject flooding. In these cases, it is maybe cost effective
to elevate a water heater; electrical panel; heating, ventilation, and air conditioning (HVAC)
system; and/or other building component so that the building remains serviceable during frequent
flood events. The Flood module in the BCA Tool can be used to analyze this type of project by
appropriately adjusting the DDF. The project cost should be limited to the scope of elevating the
utility (versus the entire building). Depending on the frequency of flooding, these projects are
typically cost effective because they are relatively inexpensive (especially if the utilities are
continuously damaged by flooding).
See section B.8 for FEMAs policy to streamline the BCA process for elevation type mitigation
projects.
floor elevation. However, the total project cost must include all documented costs, including the
cost to demolish the existing building and the total reconstruction cost.
It is important to evaluate cost effectiveness and maximize the extent of elevation during
reconstruction to reduce flood damage resulting from future conditions, such as sea level rise,
erosion, and development impacts. In 2006, the American Institutes for Research prepared a
study that assessed the cost of adding freeboard at the time of construction. The Evaluation of the
National Flood Insurance Programs Building Standards (AIR 2006) found the additional costs
are modest compared to the benefit. In addition, the study found that property owners who
incorporate freeboard recover their investment through flood insurance premium discounts in
just a few years (3 to 8 years, depending on flood zone and building characteristics). Although
insurance premium reductions are not eligible benefits for a FEMA BCA, they should be
considered an additional benefit to the building owner.
One additional consideration for reconstruction projects is the benefits associated with other
hazards (wind and seismic). A reconstructed building will be built to the latest building codes.
Depending on the age of the existing building, the reconstructed building maybe less vulnerable
to wind and seismic loads. These benefits can be captured using the Wind and Seismic modules
in the BCA Tool.
Dry Mitigation
Elevation
Floodproofing Reconstruction
Dry Mitigation
Elevation
Floodproofing Reconstruction
o Using National Flood Insurance Program (NFIP) BureauNet Data (Section 2.1.4)
Provides guidance on retrieving flood insurance policy claims data from a Web-
based database that contains information on all NFIP claims since 1978. This can
be helpful when flood hazard data or a building elevation is unavailable to help
estimate damages based on flood depths; historical damages are used instead.
Flood Module
o Counting Damages for Finished or Unfinished Basements (Section 2.2.1)
Provides assistance with properly adjusting DDFs for residential buildings with
finished basements. Appropriately applying DDFs is important to properly
estimating damages when mitigating a building with a basement.
For large-scale projects where multiple buildings are being mitigated, it is important to consider
combining the benefits and costs associated with all the buildings. The BCA Tool and the
Hazard Mitigation Assistance Unified Guidance (FEMA 2010a) allow for calculating an
aggregate benefit-cost ratio (BCR) for projects that address multiple structures. An aggregate
BCR is calculated by dividing the total net present value of benefits for each structure by the
total project cost estimate. Aggregation of benefit and cost values is allowed if the structures are
vulnerable to damage as a result of similar hazard conditions. A key factor in analyzing projects
with multiple buildings is to consider the likelihood of any buildings dropping out throughout
HMA project implementation process (see figure 7-1). In some cases, high-risk buildings
dropping out can jeopardize the cost effectiveness of the entire project.
provides a methodology to streamline the benefit cost analysis for certain mitigation project
types. This methodology was based on FEMAs Risk Reduction Division analysis of 11,000
acquisition and elevation projects. FEMA has determined that the average benefits for each type
of project are $276,000 and $175,000, respectively (2013 dollars). Therefore, FEMA has
determined that the acquisition or elevation of a structure located in a 100-year floodplain (as
delineated on the FIRM or based on best available data) that costs less than or equal to the
average benefit listed above is considered cost effective. For projects that contain multiple
structures, the average cost of all structures in the project must meet the stated criterion. There is
no need for applicants to conduct a separate BCA for a structure that meets this criterion.
Resources
FEMA Hazard Mitigation Assistance (HMA) Programs
Benefit-Cost Analysis http://www.fema.gov/benefit-cost-analysis
Benefit-Cost Analysis Helpline http://www.bcahelpline.com
Environmental Planning and Historic http://www.fema.gov/environmental-planning-and-historic-
Preservation preservation-program
Flood Mitigation Assistance Program http://www.fema.gov/flood-mitigation-assistance-program
Hazard Mitigation Assistance Overview http://www.fema.gov/hazard-mitigation-assistance
Hazard Mitigation Assistance Helpline Telephone: (866) 222-3580
E-mail: hmagrantshelpline@dhs.gov
Hazard Mitigation Assistance policies http://www.fema.gov/hazard-mitigation-assistance-policy
Hazard Mitigation Grant Program http://www.fema.gov/hazard-mitigation-grant-program
Increased Cost of Compliance coverage http://www.fema.gov/national-flood-insurance-program-2/increased-
cost-compliance-coverage
Pre-Disaster Mitigation Program http://www.fema.gov/pre-disaster-mitigation-grant-program
FEMA Building Science Publications and Other Resources
Community Rating System http://www.fema.gov/national-flood-insurance-program-community-
rating-system
Community Rating System Resource Center http://training.fema.gov/EMIWeb/CRS/
FEMA Building Science Branch http://www.fema.gov/building-science
FEMA Library http://www.fema.gov/resource-document-library
FEMA P-787, Catalog of FEMA Flood and Wind http://www.fema.gov/media-library/assets/documents/12909
Publications, and Training Courses
Flood Insurance Studies http://www.fema.gov/floodplain-management/flood-insurance-study
Flood Insurance Rate Maps http://www.fema.gov/floodplain-management/flood-insurance-rate-
map-firm
Information and Guidance on Building Safer http://www.fema.gov/safer-stronger-protected-homes-communities
Map Service Center http://msc.fema.gov/
Mitigation http://www.fema.gov/what-mitigation
Mitigation Assessment Team Reports http://www.fema.gov/fema-mitigation-assessment-team-reports
Mitigation Planning http://www.fema.gov/hazard-mitigation-planning-overview
National Flood Insurance Program http://www.fema.gov/national-flood-insurance-program
National Flood Insurance Program Technical http://www.fema.gov/national-flood-insurance-program-2/nfip-
Bulletins technical-bulletins
National Preparedness Directorate National http://www.training.fema.gov/
Training and Education
A
AHJ authority having jurisdiction
ASCE American Society of Civil Engineers
AST above ground storage tank
B
BCA Benefit-Cost Analysis
BCR benefit-cost ratio
BFE base flood elevation
C
CFR Code of Federal Regulations
D
DDF depth-damage function
DEHP bis(2-ethylhexyl)phthalate
DFA Damage Frequency Assessment
DFE design flood elevation
E
EHP environmental and historic preservation
EO Executive order
F
FEMA Federal Emergency Management Agency
FIRM Flood Insurance Rate Map
FMA Flood Mitigation Assistance Program
ft feet
G
GSTF Greatest Savings To the Fund
I
IBC International Building Code
ICC Increased Cost of Compliance
IEBC International Existing Building Code
IRC International Residential Code for One- and Two-Family Dwellings
L
LHSM lowest horizontal structural member
LiMWA Limit of Moderate Wave Action
N
NEPA National Environmental Protection Act
NFIF National Flood Insurance Fund
NFIP National Flood Insurance Program
NFPA National Fire Protection Association
NRHP National Register of Historic Places
P
PCB polychlorinated biphenyl
PDM Pre-Disaster Mitigation Program
S
SFHA Special Flood Hazard Area
SHPO State Historic Preservation Officer
T
TB Technical Bulletin
U
UST underground storage tank