The Site Is Part of the Building's Environmental Performance - Sustainable Site Design Reduces Stormwater, Heat, and Habitat Impacts
Sustainable design does not begin at the building wall - it starts at the property line and beyond. How the site is graded, how stormwater is managed, what surfaces are paved and what are pervious, how much native vegetation is retained or restored, and how the building's roof and hardscape affect local temperatures all contribute to the building's total environmental impact. The LEED Sustainable Sites credit category addresses these impacts with credits for stormwater management, heat island reduction, habitat restoration, open space, and construction activity pollution prevention. The ARE PPD tests sustainable site strategies as part of the building performance and sustainable design content area, asking candidates to identify which site strategies reduce specific environmental impacts and which LEED credits they support.
Stormwater Management
Conventional development converts permeable ground to impervious paved and roofed surfaces, dramatically increasing stormwater runoff volume and peak flow rate. This increased runoff degrades receiving waterways (erosion, sedimentation, thermal pollution, pollutant transport). Sustainable stormwater management reduces or eliminates this increase through low-impact development (LID) strategies: Bioswales and rain gardens: Vegetated depressions that slow, infiltrate, and filter stormwater runoff. Bioswales along parking lots and roadways replace conventional curb-and-gutter drainage. Pervious pavement: Pervious concrete, permeable asphalt, or modular paving systems allow stormwater to infiltrate through the pavement surface into a stone reservoir or into the subgrade. Green roofs: Vegetated roof systems retain a portion of rainfall (30-75% depending on media depth and plant coverage) through evapotranspiration and temporary storage in the growing media. Cisterns and retention: Collect and hold stormwater for irrigation reuse or timed release. LEED v4 Sustainable Sites credits SS: Rainwater Management awards credits for retaining (through infiltration, evapotranspiration, or capture for reuse) the 95th percentile 24-hour storm event runoff on site.
Heat Island Reduction
Urban heat island effect occurs when the high proportion of heat-absorbing dark paved and roofed surfaces in urban areas raises ambient temperatures 2-10°F above surrounding suburban and rural areas. This increases cooling energy demand and outdoor thermal discomfort. Mitigation strategies: Hardscape: Specify paving materials with Solar Reflectance Index (SRI) of 29 or higher for non-roof hardscape; use shading from trees or structures. Roof: Specify roofing membrane with high SRI (white TPO: SRI 78+ typical) for non-vegetated roofs; use green roofs, which eliminate heat island effect on the vegetated area entirely. LEED SS: Heat Island Reduction awards points for achieving SRI thresholds on a percentage of hardscape and/or providing shade trees.
Site Ecology
LEED SS credits for site ecology: Open Space (provide outdoor space equal to 30% of total site area including building footprint); Site Development - Protect or Restore Habitat (use native or adaptive plant species for 75% of the landscaped area; restore a percentage of the previously developed site area to natural habitat). Native and adaptive plantings require less irrigation and maintenance than non-native ornamentals and support local biodiversity.
Key Exam Points
- Stormwater management: bioswales, rain gardens, pervious pavement, green roofs, cisterns; retain 95th percentile storm event for LEED.
- Heat island - hardscape: paving SRI ≥ 29, shading trees.
- Heat island - roof: white membrane (SRI 78+) or green roof; TPO preferred cool-roof membrane.
- Site ecology: native plantings; habitat restoration; open space ratio.
- LEED Sustainable Sites: major credits category including stormwater, heat island, habitat, open space, light pollution.
AREprep's PPD sustainable design content covers sustainable site strategies, LEED Sustainable Sites credit requirements, stormwater LID techniques, heat island mitigation, and site ecology design - giving ARE PPD candidates the sustainable site knowledge the exam tests in building performance scenario questions where the correct answer requires identifying the site strategy that addresses a described environmental impact or meets a LEED credit threshold.
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