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Guideline S.12: Heat Island Reduction

Intent

To help reduce heat islands (thermal gradient differences between developed and undeveloped areas) to minimize impact on microclimate and human and wildlife habitat.

Recommended Performance Criteria

Guidelines apply to all projects designated New Buildings and Major Renovations with roof or impervious surface replacement.

  1. Reduce heat islands on non-roof site surfaces. Meet one of the paths below:
    1. Path 1: Provide any combination of the following characteristics for 50% of the site hardscape:
      1. Surface composed of light colored/high albedo (reflectance is 0.30 or greater).
      2. Surface composed of an open-grid pavement system (less than 50% impervious).
      3. 50% of non-parking surfaces shaded within five years.
      4. 50% of parking surfaces shaded within ten years.
    2. Path 2: provide 100% of non-circulation parking surface shaded within ten years.
    3. Path 3: A minimum of 50% of parking spaces placed underground or in a structured parking facility.
  2. Reduce heat islands on roof surfaces. Meet one of the paths below:
    1. Path 1: Use ENERGY STAR roof-compliant, high-reflectance, AND high emissivity roofing (initial reflectance of at least 0.65 and 3-year-aged reflectance of at least 0.5 when tested in accordance with ASTM #903 and emissivity of at least 0.9 when tested in accordance with ASTM 408) for a minimum of 75% of the roof surface.
    2. Path 2: Install a “green” (vegetated) roof for at least 50% of the roof area.
    3. Path 3: The two paths above can be combined by the following formula: (high albedo roof Area/0.75) + (green roof area/0.5), the project is compliant if this area is greater than or equal to total roof area.

Implementation in the Design Process:

During site selection, consider sites where existing vegetation or site features provide shading that can be integrated into the built area. Also evaluate effects of maturing plantings or changing uses on future heat island effects. Consider sharing building space or amenities, such as parking, to minimize the development footprint and surfaces that promote the heat island effect.

Through the design process preserve or propose landscape features that provide shade for surfaces that contribute to the heat island effect. Orient the building and pavement surfaces that maximize shade for surfaces that contribute to the heat island effect. Minimize building and pavement surfaces that are exposed to the sun. Consider replacing impervious surfaces (i.e., roofs, sidewalks, roads, driving lanes, etc.) with open-grid paving or high albedo materials. Consider replacing roofing surfaces with high albedo materials or vegetated surfaces.

Monitor submittals for compliance with plans and details. Make bidders aware of specific requirements for heat island reduction.

During occupancy, monitor and maintain vegetation around site to preserve its beneficial effects and mitigate negative developments.

Final Design:

  • S.12A: Site area of hardscape, high albedo hardscape, open-grid pavement area, non-parking hardscape areas shaded at five and ten years and underground parking areas.
  • S.12B: Total roof area, green roof areas, and high albedo roof area.

Green Roofs for Healthy Cities: www.greenroofs.org

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