Building Damage Issues in Hurricanes

Timothy P. Marshall, P.E.*

Haag Engineering Company

1. INTRODUCTION

The assessment of property damage begins

immediately after a hurricane. Homeowners, insurance
adjusters, contractors, engineers, and architects
examine buildings and their surroundings to determine
the extent of wind and water damage. While
catastrophic damage is easy to recognize, the more
subtle signs of building distress are not. Many types of
building distress that are inherent to different
construction materials are not recognized until after a
hurricane occurs and are erroneously linked to the
storm. The purpose of this paper is to summarize some
of the more common building damage issues witnessed
during the author's inspections of thousands of
hurricane-damaged structures from more than a dozen
hurricanes since 1980.
Figure 1. Examples of wind (a) and wave (b) damage
In order to conduct an accurate damage assessment, it to houses. Relative forces are illustrated on left with
is important to have knowledge of building height above the ground.
construction, building materials, and environmental
factors, as well as an understanding of wind and water Wind interacting with a building is deflected over and
forces. Seaquist (1980) addresses some of the inherent around it. Positive (inward) pressures are applied to
deficiencies in building construction and how to the windward walls and try to push the building off its
recognize such problems. Many people focus on the foundation. Therefore, it is important that the building
highest wind speeds associated with the storm without be anchored properly to its foundation to resist these
regard to the type, height, location, and exposure of the lateral forces. Negative (outward) pressures are
measuring equipment. Powell et al. (1994) discusses applied to the side and leeward walls. The resulting
the problems associated with extrapolating wind "suction" forces try to peel away siding. Negative
reports from one location to another after Hurricane (uplift) pressures affect the roof especially along
Andrew. windward eaves, roof corners, and leeward ridges.
These forces try to uplift and remove the roof covering.
2. WIND VS. WAVE DAMAGE The roof is particularly susceptible to wind damage
since it is the highest building component above the
One issue in assessing hurricane damage is determining ground. Wind pressures on a building are not uniform
whether wind effects or wave forces or a combination but increase with height above the ground. Damage to
of both damaged a building. Typically, this issue arises a building caused by wind typically begins at roof level
since there are separate insurance policies for wind and and progresses downward and inward with increasing
wave damage. Not every building owner has insurance wind velocities. Thus, the last place wind damage
coverage for both damage types. Therefore, an occurs is to the interior of the structure.
accurate determination of the causes and extent of
building damage must be made. Wind and wave forces Wind damage begins with such items as television
affect a building differently. Wind forces are highest at antennas, satellite dishes, unanchored air conditioners,
roof level whereas wave forces are greatest at the base wooden fences, gutters, storage sheds, carports, and
of the building. Refer to Figure 1. FEMA (1989) has a yard items. As the wind velocity increases, cladding
detailed document showing how to recognize wind and items on the building become susceptible to wind
wave damage to a building. damage including vinyl siding, roof coverings,
___________ windows, and doors. Only the strongest winds can
*Corresponding author address: Timothy P. Marshall, damage a properly designed and well-constructed
Haag Engineering Co., 2455 S. McIver Dr., Carrollton, building. Marshall et al. (2002) describes the various
TX 75006. Email: timpmarshall@cs.com failure modes in buildings caused by high winds.
Water forces are greatest at the base of a building and changes in the underlying soil or settlement. Concrete
tend to undermine the foundation and destroy the slabs float on the ground and rise and fall with
supporting walls, thereby leading to collapse of part or expansion and contraction of the underlying soil. As
all of the building. Moving water exerts much greater expansive soil dries around the foundation perimeter,
force than air at the same velocity. One square foot of the perimeter of the building settles relative to the
water traveling at ten miles per hour possesses as much center leading to distress in the interior and exterior
kinetic energy as a 280 m.p.h. wind. Homes along the finishes. Mitered corners at frieze boards open and
coastline are at greatest risk of being damaged by interior doors bind. Cracks in plaster and gypsum
waves. FEMA (1997) found that over one hundred board frequently emanate from the corners of door and
oceanfront homes were washed off their foundations window openings. Slab cracks can extend through
during Hurricane Fran. Even homes elevated on brittle finishes bonded to the slab like ceramic tiles.
pilings above the waves collapsed or leaned
precariously when four to six feet of sand had been An examination of the crack interior will often
scoured around pilings that were only driven eight feet determine whether the crack is new or old. Cracks
deep. become discolored with time as they accumulate dirt,
paint or debris. Refer to Figure 2. Edges of the cracks
Water also can lift wooden buildings on pier and beam become rounded with continued wear. Water entering
foundations, as they are buoyant and will float. The the cracks can lead to rusting of reinforcing steel and
author observed numerous homes that floated landward the resulting expansion can lead to spalling the
or out to sea depending on the wind direction during concrete. In contrast, cracks caused recently do not
Hurricane Hugo. Such homes floated when the water have these characteristics. Recent cracks appear fresh
level reached about eight inches above the finished and unweathered with broken pieces of the concrete
floor. Wooden-framed homes with brick veneer walls along the fractures. Concrete slab cracks associated
tended to rise and sink within the brick veneer shell. with wind usually are found in the direct load path with
The house invariably did not come back to the same failure of a building component. Refer to Figure 3.
position causing distortion of the wooden frame. Wind
did not cause this condition. It is important to
determine the height of the water level during the storm
in conjunction with time, wind direction, and wind
speed relative to the building location.

3. CRACKS IN CEMENT-BASED MATERIALS

People examining their building after a hurricane

invariably find cracks in concrete slab floors, brick and
concrete masonry walls, stucco, etc. For insurance
reasons, it becomes important to delineate between Figure 2. Old crack in middle of concrete slab (A) and
cracks inherent to the building from cracks that were close-up view (B) showing dirt in crack. This crack
caused by the storm. There are many kinds of cement- was not caused by the hurricane.
based materials used in building construction like
concrete, concrete block, mortar, stucco, and plaster.
These materials tend to crack during or after curing as
they shrink. The extent of shrinkage cracking depends
primarily on the water content of the mix and
placement of control joints. Environmental factors
such as the rate of hydration and evaporation can affect
the severity of shrinkage cracking. For these reasons,
shrinkage cracks are fairly common in cement-based
materials. Shrinkage cracks are usually small in width,
less than an eighth of an inch, but can extend several Figure 3. New crack in concrete slab caused by the
feet in length. rotation of the steel column that failed in the wind.
3.1 CONCRETE SLAB CRACKS 3.2 MASONRY DISTRESS
Many buildings are constructed on thin concrete slabs Masonry walls commonly are constructed with fired-
with shallow footings and therefore are susceptible to clay brick or concrete masonry units (CMU) bonded
differential foundation movement from cyclic moisture together by mortar. Mortar is a mixture of Portland
cement, sand, water, and lime. The lime is utilized to
increase workability of the mix. Masonry walls are
susceptible to distress from differential (up and down)
foundation movement. Drainage conditions, locations
of trees and downspouts all affect the soil moisture
content. Window and door openings are naturally weak
points in the wall where the distress concentrates.
Cracks and separations that open with height (V-shape)
indicate settlement on either side of the crack whereas
Figure 5. Windward masonry wall pushed inward by
cracks tapering closed with height indicate settlement
the wind (A), and leeward wall that fell outward (B).
at the base of the crack. Refer to Figure 4.
Note brick ties (circled) did not engage the masonry.

Non-loadbearing brick masonry walls that are not

anchored to the building can be flexed relatively easily
when pushed by hand. The wall has not been
"loosened" by the wind; it just never was anchored.

Foundations on soil fill are quite prone to settlement

especially if the soil is not uniformly compacted.
Heavy masonry walls and chimneys are prone to
Figure 4. Foundation settlement at the corner of a rotating away from a building as the underlying soil
house (A). Close-up view (B) shows V-shaped gap settles. Leaning walls or chimneys can be mistaken as
between window and brick, and (C) shows stair-step being caused by the hurricane. However, masonry
crack at base of window. Note prior attempts at caulk chimneys typically fail along horizontal mortar joints
repair. The distress was not caused by the hurricane. and topple to the leeward side of the hurricane winds.
Failure of the chimney occurs where the chimney
Masonry walls are also susceptible to volume changes intersects the roof or where the mortar joints are
from varying temperature and must have the necessary weakest. In general, mortar joints are weak in tension
control joints to alleviate thermal strains and reduce and can be pulled apart relatively easily. Refer to
cracking. Brick walls expand when heated and shrink Figure 6.
when cooled with the greatest movement occurring in
the long dimension of the wall. Thermally induced
cracks tend to form near wall corners and openings
where strains are concentrated. The Brick Institute of
America (1991) recommends installing control joints
every 15 to 20 feet along a wall to minimize cracking
from thermal strains. Mortar joint cracks also are
associated with steel lintels over doors and windows.
Steel lintels expand and contract at different rates than Figure 6. Leaning chimney from foundation
the masonry. Also, rusting of the steel causes settlement (A) and broken chimney from wind (B and
expansion that can force apart the mortar joint. Old C). The letter "F" indicates the failure location.
masonry cracks become discolored with time as they
accumulate dirt, paint or debris. In contrast, recent 3.3 STUCCO CRACKS
cracks appear fresh and unweathered with broken
pieces of masonry along the fractures. Stucco is similar to mortar, typically one part Portland
Cement to three parts sand with about ten percent lime.
Masonry walls are susceptible to wind damage Stucco is commonly applied over an expanded wire
especially if they are non-loadbearing. Such "free- mesh that has been fastened to the sidewall of a
standing" walls are pushed in on the windward side and building. The stucco is troweled over the mesh using
fall outward on the leeward side. Masonry walls either a two-coat or three-coat process. Total thickness
should have wall ties to anchor the walls to the frame, of the stucco should be between 3/4 and one inch.
however, the author has observed many buildings that The appealing aspect of stucco is its low maintenance
did not have such ties or did not have them engage the and resistance to deterioration. Various finishes and
masonry. Refer to Figure 5. colors can be added. Cracks in stucco can also be
repaired relatively easily (PCA, 1980).
Stucco frequently is applied over concrete, concrete 4. FOGGED INSULATED GLASS
block masonry, or wood. Quality control is essential
to ensure proper performance. The addition of too People occasionally find "fogged" insulated glass
much water can lead to shrinkage cracks or crazing. windows after a hurricane. In order to determine
Also, stucco is not very flexible and will mirror whether the unit failed as a result of hurricane winds or
underlying discontinuities in the wall. Therefore, not, an inspection of the unit and its surroundings must
proper control joints must be installed to prevent such be performed.
cracks. Finished stucco also is porous and will absorb
moisture. Therefore, stucco should not be in constant Insulating glass assemblies are comprised of two glass
contact with water. Otherwise, the underlying metal panes separated by an aluminum spacer around the
lath can rust causing the stucco to delaminate. Such perimeter. The spacer is cemented to the two panes
stucco damage usually occurs on wing walls and with primary and secondary seals. A moisture
balconies that project from building overhangs. Old absorbent material (desiccant) is contained within the
stucco cracks contain dirt or paint, and fracture air space. This gas will expand and contract with
surfaces are discolored. In some instances, rust or changes in temperature placing stresses on the seals.
mildew emanates from the cracks. Refer to Figure 7. Exposure to ultraviolet rays and moisture also can
affect the seals. Spetz (1992) showed several
manufacturing deficiencies in the making of insulated
glass like "skipped" areas on the primary and second
seals, improper spacer coverage, and spacer
misalignment. Smith (1993) concluded that improper
installation and handling procedures commonly cause
seal failures. Fogging of the window forms as
moisture condenses in the air space between the glass
panes causing the unit to become dull or opaque
(Figure 9).

Figure 7. Old cracks in stucco: at the base of the wall

where there is an underlying joint between the bottom
plate and foundation (A), paint in crack (B), and
mildew in crack (C).

Hurricane winds can cause cracks in stucco especially

where the stucco bridges a joint that flexes (Figure 8).
Fresh stucco cracks are sharp and unweathered.
Merging cracks occasionally contain loose pieces of
the stucco material. Localized damage can occur
Figure 9. Mineral residue inside "fogged" window
where flying debris strikes the stucco clad wall.
unit indicated the seals failed quite some time ago.

Typically, windows with southern and western

exposures are more susceptible to fogging because of
extreme temperature (expansion/contraction) changes
and UV degradation of the sealants. The presence of
mineral build-up or "scum" between the panes
indicates the unit failed a long time ago.

High winds from a hurricane can cause or promote seal

failure. Such glass damage increases with height above
the ground and occurs in high positive and high
Figure 8. Fresh crack in stucco wall after hurricane negative pressure zones. Typically, winds strong
where it bridged a joint between the bottom of the enough to break window seals also can break the glass.
gable framing and the underlying concrete tie-beam
(A). Note unweathered condition of crack and loose 5. REFERENCES (available upon request)
pieces of stucco (B).