Guidance For Calculating Outdoor Water Use Reduction030309
Guidance For Calculating Outdoor Water Use Reduction030309
Guidance For Calculating Outdoor Water Use Reduction030309
This guidance document provides an overview of the calculation procedures for estimating the
reduction in outdoor water use achieved from sustainable landscaping and irrigation system designs.
These calculations must be completed if the project team intends to take credit for SS 2.5 or WE 2.3,
even if the project does not intend to install an irrigation system. These calculations must be
performed by a landscape professional, which includes individuals with certification, licensure,
formal training (higher education), or at least 10 years of professional experience.
The landscape professional or irrigation specialist must sign the Accountability Forms for SS 2.5 (and
WE 2.3), and submit the calculations to the LEED Canada for Homes Provider. Alternatively, he/she
may complete the “LEED Canada for Homes Calculator for Percent Reduction in Outdoor Water Use”,
including the signature, and submit this to the Provider, in lieu of the Accountability Form.
The same calculation is performed in SS 2.5 and WE 2.3. Full points must be earned in SS 2.5
before any points are earned in WE 2.3. WE 2.3 cannot be pursued unless SS 2.5 is pursued.
Terminology
Please note that some of the terms used in this guidance replace terms used in the LEED Canada for
Homes Rating System and Reference Guide. This was done to more accurately describe the
components of this calculation, and updated versions of the Rating System and Reference Guide will
incorporate this new terminology.
The calculation process required to demonstrate compliance with SS 2.5 and WE 2.3 can be
summarized in four steps, which are provided below. For more information, please review “A
Guide to Estimating Irrigation Water Needs of Landscape Plantings in California” (or “WUCOLS”
document), available from the CA Dept of Water Resources under the Publications link at:
http://www.owue.water.ca.gov/landscape/
Step 1. Calculate the outdoor water demand for the landscaping for
the baseline.
Definition: The baseline outdoor water demand is the amount of water that would be lost
through evapotranspiration if the given landscaped area were planted with a reference
grass. The baseline depends on:
Reference Evapotranspiration Rate (ET0) for your region. The ET0 value for July
must be used.
The ET0 is regionally specific. A region that is cool or humid will have a lower ET0
than one that is hot and dry.
ET0 is based on the water lost from a medium-height, cool-season grass growing in
an open field in the region.
Typical ET0 values are often available from a local or state Department of
Agriculture.1 Or contact an expert: www.irrigation.org/gov/ET_list.htm
The month of July is used, because it is generally the month with the highest water
needs.
The Baseline outdoor water demand is calculated with the following equation (performed
automatically by the LEED Canada for Homes Calculator):
Where: Landscaped Area is in ft2, and ET0 is in inches per month. The 0.62 is
a conversion factor (converts ft2*in/mo into gal/mo).
1
If the landscape professional has difficulty finding the ETo for the region, please contact your Provider.
Definition: For the purposes of this document, a landscape zone is an area within which
all plantings will require the same amount of water. Zones may or may not be divided
into separate parcels on the actual lot.
In this calculation the landscaped area must be divided into zones, as appropriate. If
there are slightly different water needs within a zone, the calculation for that zone should
be based on the highest water needs within it. To avoid this, when designing landscape
zones, take into account variations in:
Types of plants
Microclimates (e.g., differences in shading)
In addition, the following affect irrigation efficiency and should also be considered for
each zone.
Type and efficiency of irrigation systems
Irrigation system controls
The four variables above affect outdoor water use, and each is characterized by a
different “factor” that is used in the calculation. Descriptions and example values for
each factor are given in Exhibit 1. These factors are used in the equation in Step 2b.
Step 2b. Calculate the outdoor water use for each landscape zone.
This calculation must be conducted for each zone, using values for Landscape Area, KS,
KMC, IE, and CF that are specific to each zone.
Please note that CF is only applicable if there are controls. If there are no controls, CF
should equal 1.0. If there is no irrigation system, use the appropriate default IE value
provided in Exhibit 1. (IE is calculated automatically by the LEED Canada for Homes
Calculator).
Sum the outdoor water use from all of the zones, using the following formula (performed
automatically by the LEED Canada for Homes Calculator):
Design Case outdoor water use = outdoor water use for zone 1+ outdoor water use
for zone 2 + outdoor water use for zone 3 + … (all zones)
Percent reduction = 1 – (Design Case outdoor water use / Baseline outdoor water
demand) * 100%
If a project meets SS 2.2 parts (b), (c), (d), and (e), one additional point may be
counted in ID 3.
If a project exceeds the maximum value in WE 2.3, exemplary performance
points may be earned (to be counted in ID 3) according to the following:
o one point for 65% reduction
o two points for 70% reduction
o three points for 75% reduction
o four points for 80% reduction
2
Factor Description Range of Guidance in Choosing Values
Values
The species factor reflects the If the landscape professional is familiar with the KS values for the species
amount of water that the species of planted, use those values. Otherwise, use the values from Table 6 in SS 2.5 as
plant needs. follows. For a vegetation type, choose:
A high value is used for plants that o The low value for a species that needs less water than most plants of
need a lot of water. A low value is that type. For example, for drought-resistant shrubs that use little water,
used for plants that need little water. choose the Low value for Shrubs: 0.2
o The average value for a species that needs a typical amount of water for
KS As a general rule of thumb, species 3 that type. For example, for a flowerbed with typical water needs for
0.2-0.9
requiring the following amounts of flowers, choose the Average value for Groundcover: 0.5
water are designated as follows*: o The high value for a species that needs more water than most plants of
o 70-90% ETo : High Ks that type. For example, for a fruit tree that needs to be watered often,
o 40-60% ETo : Moderate Ks choose the High value for Trees: 0.9.
o < 30% ETo : Low Ks
*Source: the WUCOLS document If a landscape zone is planted with different species that have different KS
values, use the highest KS value for the calculation. Also, this indicates that the
Base estimates on expected demand landscape design could be improved. Consider substituting the highest KS
when plants are fully mature. species with a lower KS species.
The microclimate factor describes If the landscape professional is familiar with how KMC values are applied, use
how conditions such as sun and wind 0.5-1.5 those values. Otherwise, use the values from Table 7 in SS 2.5 (or Table 13 in
affect the demand for water. WE 2.3) as follows. Choose:
For most
KMC A high value is used for areas in situations, o Low, KMC = 0.8, if zone shaded, on the north side of a building, and/or
direct sun, high winds, or receiving choose from protected from the wind (e.g., courtyards).
heat from reflective surfaces. A low 0.8, 1.0, o Average, KMC = 1.0, if zone sometimes shaded and in moderate winds.
4
value is used for areas in shade or or 1.2 o High, KMC = 1.2 if zone sunny, windy, receiving reflected heat, and/or on
protected from the wind. the south side of a building.
2
The Tables referenced are in the Rating System. These tables are numbered differently in the Reference Guide.
3
Ks values < 0.2 are not acceptable. Plants such as drought-resistant, native species can appear stressed (e.g., wilted) during long periods of hot, dry weather. Although
these species survive in the wild, homeowners may choose to water them, so that they appear more healthy. Consequently, the water use for these plants is not 0.
4
For extraordinary conditions, the following may be used: Extremely well-protected and shaded, KMC = 0.5; extremely sunny and windy, KMC = 1.5.
Example 1
A home in Sacramento, CA has a 1000 ft2 rectangular yard. Half of the yard is planted with
bushes that are not drought tolerant, and that have typical water needs. The other half is
planted with drought-resistant, native wildflowers that will rarely require water beyond
precipitation. The entire yard is in partial shade, and winds are normal.
Rotors are installed to water the bushes. The system includes flow-control sensors that result
in 15% water savings, according to documentation from the manufacturer. The system was
installed by an irrigation professional. This person was not WaterSense certified, and it was
not verified by a 3rd party as distributing water evenly. The irrigation system includes 3 of the 6
listed distribution measures.
From “A Guide to Estimating Irrigation Water Needs of Landscape Plantings in California” (the
“WUCOLS” document), for July in Sacramento, CA:
= 8.7 in/month
The LEED Canada for Homes Calculator for Percent Reduction in Outdoor Water Use was
then used to complete Steps 1, 2, 3, and 4. The calculations are presented below. As shown,
the reduction in outdoor water use was 54%, which corresponds to 6 points in the SS 2.5
section, and 2 points in the WE 2.3 section.
Legend
Step 2a: Select appropriate inputs for each zone in the design case
Choose appropriate values for species factor (KS), microclimate factor (KMC), irrigation efficiency (IE), and control factor (CF): Divide
landscaped area into landscape zones. For each zone, enter the descriptions, and use them to choose a value for each factor. Please refer
to the guidance document for more information about how to choose these values.
Notes: 1) Well-designed landscaped areas have zones designed so that all plants within each zone will need the same amount of water. 2)
Many projects will have fewer than 10 zones. Leave unused rows blank. For projects with > 10 zones, please contact your Provider. 3) For
boxes with pull-down menus, choose from the list. Do not type in information. 4) The fly-out directions box can be moved by dragging it.
Step 2b: Calculate the outdoor water use for each zone in the design case
Enter the area for each landscape zone in square feet.
Step 2c: Calculate the total outdoor water use for the design case
This step is completed automatically. If the error checker below indicates an error in the calculation, or if the Total outdoor water demand is
0, please review the inputs and assumptions above.
SS 2.5 points 6
WE 2.3 points 2
The project has decided to use native species for most landscaping. The front yard will have
two 5x5 areas: one planted with a non-native, ornamental fruit tree, the other with a native oak
tree that has typical water needs for a tree. The remainder of the front yard will be planted
with a mix of wildflowers and shrubs that are all drought-resistant: All will rarely require water
beyond precipitation. The backyard will be planted with this same mix.
A drip system is installed for the wildflower / shrub mix in the back yard, and for the landscape
zones in the front yard that are planted with trees. The system was not verified by a 3rd party,
and it was not installed by a WaterSense professional. It includes 2 of the 6 distribution
measures.
Because they are in shade, and have low water needs for their species, there is no irrigation
system for the wildflower / shrub mix in the front yard.
From http://texaset.tamu.edu/pet.php, for July in College Station, TX, ET0 = 7.1 inches for the
month of July.
The LEED Canada for Homes Calculator for Percent Reduction in Outdoor Water Use was
then used to complete Steps 1, 2, 3, and 4. The calculations are presented below. As shown,
the reduction in outdoor water use was 70%, which corresponds to 6 points in the SS 2.5
section, 4 points in the WE 2.3 section, and 2 points in the ID 3 section.
Legend
User input cell Calculated cell
Step 2a: Select appropriate inputs for each zone in the design case
Choose appropriate values for species factor (KS), microclimate factor (KMC), irrigation efficiency (IE), and control factor (CF): Divide landscaped
area into landscape zones. For each zone, enter the descriptions, and use them to choose a value for each factor. Please refer to the guidance
document for more information about how to choose these values.
Notes: 1) Well-designed landscaped areas have zones designed so that all plants within each zone will need the same amount of water. 2) Many
projects will have fewer than 10 zones. Leave unused rows blank. For projects with > 10 zones, please contact your Provider. 3) For boxes with
pull-down menus, choose from the list. Do not type in information. 4) The fly-out directions box can be moved by dragging it.
Step 2b: Calculate the outdoor water use for each zone in the design case
Enter the area for each landscape zone in square feet.
Step 2c: Calculate the total outdoor water use for the design case
This step is completed automatically. If the error checker below indicates an error in the calculation, or if the Total outdoor water demand is 0, please
review the inputs and assumptions above.
SS 2.5 points 6
WE 2.3 points 4