Sustainable Concrete Solutions Contribute to LEED for Homes Certification: Part I
By: Donn C. Thompson AIA, LEED AP
Residential architects and builders have the first Leadership in Energy & Environmental Design (LEED) based sustainable construction program for housing, now that the U.S. Green Building Council (USGBC) has finalized LEED for Homes. Finally, a road map exists for the systematic creation of high-performance housing, built upon the criteria of previous LEED rating systems for commercial projects, but focused on innovations and best practices for the sustainable residential marketplace. This two-part article provides a summary of how concrete technologies can provide less complicated compliance with many LEED for Homes categories, enabling designers and contractors to profitably deliver safer, long lasting, sustainable concrete solutions to new homeowners.
In this issue we will look at the overall goals of this new LEED program and the first three resource categories where concrete homebuilding systems and products can contribute to the certification of projects under the system. In the next issue, we will examine the impact concrete can have on remaining applicable certification provisions.
The final version of LEED for Homes (LEED-H) was announced by the USGBC in November 2007 at the Greenbuild International Conference and Expo in Chicago. The program is intended to cover stand-alone single-family houses, production and custom, as well as low-rise multi-family applications of three stories or less. The stated goals of the USGBC are to provide a residential sustainability system that will transform the design of mainstream homes. Designers and homebuilders can differentiate themselves by providing homes that are recognized as high-quality green homes. Homeowners can rely on an easily recognizable “brand” when purchasing a sustainable home. The various certification levels and the number of points required for a home to meet each level are shown in Table One below.
The first three of the resource categories and sub-categories in which concrete homebuilding systems can contribute to credits under LEED-H are identified below along with a description of how concrete systems can offer sustainable benefits. Table 2a provides a summary of these potential contributions.
ID – Innovation and Design Process
ID 2.1 Durability Planning – Prerequisite
As a LEED-H prerequisite, the builder is required to identify various project conditions related to weather, site drainage, potential natural disasters and the potential impact to the interior environment based on the home’s design. The homebuilder must then look for workable solutions that will ensure the long-term durability of the home and maintenance of a healthy and safe indoor and exterior environment.
The strength of reinforced concrete wall systems, both formed and cast-in-place on-site, precast off-site and trucked to the project, or built in place with modular autoclaved concrete or concrete masonry systems, will provide unparalleled disaster and wind resistance. Solid floor and roof systems deliver quiet safety and security. Unlike conventional systems, they’re inherently fire resistant, and will not promote the growth of mold and mildew, and will not decay.
But it’s more than just the structure. Finishes also have a big impact on the long-term performance of a home. On the outside, the hardness and durability of exposed cast-in-place or precast concrete, or concrete finish systems, like fiber cement siding and trim, concrete masonry, stucco, will all provide better durability to reduce the frequency and cost of replacement and maintenance. Concrete roof tiles adhere more effectively in high winds, stand up to hail, to fire, and last far longer than ordinary shingles. Inside, air tightness is improved because the continuous concrete wall systems reduce joints and penetrations. This makes it far easier to design mechanical systems to effectively maintain better indoor air quality, with more constant temperatures, and fewer drafts.
ID 2.1c Indoor Moisture Control – Prerequisite
LEED-H requires moisture resistant flooring in kitchens, baths, spa areas, and adjacent to exterior doors. Colored or stained, as well as stamped and textured, concrete floor systems can provide rich, high-quality floor finishes that will provide the water resistance needed at all of these critical locations. With other systems, wear and tear and failure of seams or joints can lead to structural decay, mold and mildew, surface damage, and expensive repairs.
ID 2.2 Durability Management – Prerequisite
During construction, a quality management process is required by LEED-H to insure systems are installed properly to provide long-term high performance. With concrete wall systems, fewer parts and pieces means less complicated assembly, requiring less skilled labor. With simpler, more straightforward methods in the field, designers and builders are better assured of achieving the quality installation required to reduce the environmental impact of the homes.
LL – Location and Linkages
LL 3.2 Infill
and/or LL 3.3 Previously Developed
Through the use of Portland cement for soil solidification and stabilization, previously contaminated sites in urban environments can be reclaimed and successfully redeveloped. The cement is used as a binder to physically and often chemically neutralize hazardous substances within contaminated soils. In this way, old industrial sites can be reclaimed and regentrified as thriving, new residential neighborhoods, integrated within the existing street, transit, and infrastructure networks.
SS – Sustainable Sites
SS 1.2b or d Minimize Disturbed Area of Site
LEED-H will award one credit for reducing the amount of disturbed area on site. On newly built sites, at least 40 percent of the buildable lot area must be left undisturbed. On previously developed sites, building on lots no larger than 1/7 acre qualifies for LEED for Homes credit. With insulated concrete basements, the amount of usable floor area can be increased without increasing the overall coverage of the house on the lot.
SS 3b Local Heat Island Effects
Average air temperatures are rising in cities, where buildings and pavement have replaced trees and vegetation that cool surface temperatures through shade and release of water that evaporates. Recent tests confirm the high solar reflectance of standard concrete. Common paving mixes reduce the impact of hardscape on local air temperature. The concrete reflects more solar energy, keeping the paved areas cooler. Far less heat energy is released into the surrounding air than darker-colored asphalt surfaces. A LEED-H home would qualify for points by incorporating the high albedo of concrete for at least 50 percent of the site hardscape.
SS 4.1b Permeable Lot
A home site qualifies for 1 to 4 LEED-H points when 70 to 100 percent of the unroofed built environment is pervious, allowing captured water runoff to be absorbed through pavements. Two types of porous concrete pavements are available, pervious concrete and permeable interlocking concrete pavements. Pervious concrete is cast-in-place using a mix that leaves significant voids to allow water to percolate through. Permeable and grid paver systems are interlocking modular pavers that can allow water to pass through gaps in the blocks or through grid openings. Both types of paving can provide the required strength and support for residential traffic while assisting in on-site absorption of runoff.
SS 4.2a Permanent
Construction of a home on a steeply sloped site can disrupt existing natural erosion control. Modular concrete masonry is an effective means for creating permanent segmental retaining walls that can be used to reestablish, preserve, and enhance the stability of steep terrain. These improvements can contribute to one LEED-H credit. The variety of available colors and textures will be a complement to landscaping as well.
SS 5 Nontoxic Pest Control
SS 5E.V Non-Cellulosic Wall Structure (other than wood of straw) AND SS 5E.VI Foundation Walls
The LEED for Homes system credits builders for homes that reduce dependence on pest control chemicals. One way to accomplish this is to utilize concrete systems for exterior wall assemblies in locations where termite infestation is identified as “moderate to heavy” or “very heavy.” This covers roughly the lower two-thirds of the contiguous United States.
Concrete provides a non-hazardous alternative to invasive, expensive, and continuous pest control measures required with wood systems in these areas of the country. Half points are awarded for use of solid concrete or concrete masonry foundations with solid top coursing. Half points are also awarded for use of concrete wall systems above grade, eliminating termite-vulnerable wood from the exterior walls altogether.
Part I Conclusion:
In Part I we have identified the objectives the US Green Building Council hopes to achieve through the release of LEED-H, its first single-family residential green building program. Concrete homebuilding technologies provide a variety of solutions to address the provisions contained in Innovation and Design Process, Location and Linkages, and Sustainable Sites. In the next issue, Part II will focus on the impact of concrete on remaining applicable LEED-H categories.