ID#5908 made on
SSc7.1 - Landscape and exterior design to reduce heat islands - non-roof
LEED BD+C: New Construction
The requirement of this credit states, "Provide shade (within 5 years) and/or use light-colored/high-albedo materials (reflectance of at least 0.3) and/or open grid pavement for at least 30% of t...
The requirement of this credit states, "Provide shade (within 5 years) and/or use light-colored/high-albedo materials (reflectance of at least 0.3) and/or open grid pavement for at least 30% of the site's non-roof impervious surfaces, including parking lots, walkways, plazas, etc.; OR place a minimum of 50% of parking spaces underground or covered by structural parking; OR use an open-grid pavement system (less than 50% impervious) for a minimum of 50% of the parking lot area." We would like to clarify the use of porous pavement, that is, an asphalt or concrete surface with voids in the poured-in-place material designed to infiltrate water, as it relates to this credit. The third option of this credit clarifies the use of an open-grid pavement system as being less than 50% impervious, but LEED does not clarify a minimum amount of imperviousness for porous pavement, in this credit or other Sustainable Site Credits. (Note that a recent feature article in Environmental Building News describes a "void space" range of 15-21% for porous concrete, and 16-20% for porous asphalt, to be properly installed over uniformly graded stone aggregate having approximately a 40% void space). Does USGBC recommend a method to translate void space of porous pavement into % pervious for LEED Credits? Can we assume that if porous pavement were used rather than open grid pavement for 30% of the non-roof impervious area, that it could meet the first option of this credit? If used for 50% of the parking lot area, would it meet the third option of this credit? If its % pervious were determined to be less than 50% and therefore not equivalent to open-grid pavement, could its perviousness be averaged over a greater area, as would be consistent with the Credit Rulings related to material albedo? Lastly, if the material is pervious, how can it at the same time contribute to being 30% of our non-roof "impervious" surfaces for the first option of the credit? That reasoning would lead one to want subtract it from the denominator of this equation, leaving a smaller area that needs to be 30% LEED-compliant. Please advise in detail.
The inquiry has posed the following distinct questions: 1) How do you determine whether or not a material qualifies as open grid pavement (less than 50% impervious)? 2) If a porous paving material is used to pave 30% of a project's non-roof impervious areas, would the project meet the requirements of the first option of this credit? 3) Can porous pavement be used to satisfy the requirements of the third option for this credit? 4) Can a pavement that is greater than 50% impervious be used over a greater area of the parking lot to comply on a weighted-average basis? Porous asphalt and porous concrete paving do not qualify as open grid paving (less than 50% impervious) under this credit and cannot be used to satisfy the third option to achieve this credit. The impervious percentage is simply the percent of surface area of installed material that is impervious. For example, the impervious percentage of paving products that combine concrete or plastic grids with grass infill is calculated as the percentage of the horizontal area of the concrete or plastic material. While porous pavements have a low "effective" imperviousness, they are considered impervious surfaces for the purposes of this credit. To achieve this credit using porous pavement, you need to demonstrate that 30% or greater of the non-roof impervious area (including the porous pavement) has a reflectance of at least 0.3. It is conceivable that an open grid pavement that is 60% impervious, for example, could be used in a greater percentage of the parking lot to comply on a weighted average basis. A CIR ruling dated 12/5/2001 provides guidance regarding the development of weighted average calculations required to demonstrate compliance with the intent of this credit. Applicable internationally.
Related Addenda (Corrections & Interpretations)