For many years, the industry has worked diligently to replace asphalt roads and parking lots with concrete by promoting its benefits, such as better visibility and cooler surfaces. Now, new research emphasizes concrete's environmentally-positive impact.
The “urban heat island” effect is a phenomenon in which a defined geographic area experiences higher temperatures than its surrounding area due to the greater heat absorption and retention of its building and paving materials. This temperature spike puts a greater demand on energy resources needed to cool the buildings in the area.
At the Greenbuild International Conference last fall, the Portland Cement Association (PCA) announced a new study of the solar reflectance of concrete and its positive impact on limiting the heat island effect. The research, conducted by the construction research organization CTL-Group, allows concrete hardscaping to contribute to LEED points for New Construction Sustainable Sites (LEED-NC SS) Credit 7.1 Heat Island Effect: Non-Roof without additional testing.
According to PCA, this work is the most comprehensive study of concrete's solar reflectance to date, and the first time it has been examined in relation to LEED points. “This study formally confirms that ordinary concrete, regardless of its ingredients, can help limit the heat island effect,” said David Shepherd, AIA, director of sustainable development for PCA. Until now, submitters had to provide their reflectivity data when applying for LEED credits.
All 45 sets of concrete samples tested met the required LEED reflectivity criteria, regardless of the mix. The mixes used a number of different components, including recycled material such as fly ash and slag cement. The solar reflectance of cement affected the concrete's solar reflectance more than any other constituent material. Supplementary cementitious material had the second greatest effect.
Heating us where we live
In terms of “non-roof” surfaces, residential areas in and around cities can contribute significantly to urban heat islands. This fact presents a tremendous opportunity for paving streets, driveways, and sidewalks with concrete rather than dark asphalt. The next step is figuring out how residential work can qualify for sustainability credit.
Under the LEED for Homes rating system, projects can earn one point if 50% or more of the horizontal hardscape areas within 50 ft of a home have a solar reflectance index (SRI) of at least 0.29. With the results of PCA's reflectivity study, any type of ordinary concrete meets this requirement (colored and stained concrete have not yet been tested).
The National Association of Home Builders (NAHB) is also developing a National Green Building Standard, with the International Code Council (ICC) and the NAHB Research Center. This effort will be an ANSI approved, voluntary standard with its own points and certification.
The standard will offer comprehensive sustainable certification for sub-division design and development, in addition to homes. It is expected to be completed this year. At the time of publication, the most recent document allowed four possible points for using a combination of shading and light paving with reflective materials in at least 50% of concrete hardscaping.
As residential green rating systems and standards develop, they will offer more ways to promote the sustainable advantage of concrete's reflectivity. “People will discover a lot of opportunities when they see different ways they can earn credits,” said Donn Thompson, AIA, LEED AP, residential technology manager for PCA.
For more information about the NAHB National Green Building Standard, visitwww.nahbrc.org/GBStandard.