Sustainable Concrete Solutions Contribute to LEED for Homes Certification
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 US 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 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.
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.
Each 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 Two 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.
Table 1 LEED for Homes
LEED for Homes Certification Levels
Number of LEED for Homes Points Required
45 - 59
60 - 74
75 - 89
90 - 136
Total Available Points
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% of the buildable lot area must be left undisturbed. On previously developed sites, building on lots no larger than 1/7th of an acre qualifies for LEED for Homes credit. With insulated concrete basements, the amount of useable 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% of the site hardscape.
SS 4.1b Permeable Lot
A home site qualifies for 1 to 4 LEED H points when 70 to 100% 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 Erosion Controls
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 or 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 2/3rds 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.
WE – Water Efficiency
WE 1.1 Rainwater Harvesting System and/or WE 1.2 Graywater Reuse System
Waste water that is not clean, but not heavily polluted, like water from laundry or bathing is called graywater. The capture and control of graywater and rainwater can greatly reduce water usage requirements for a home and site. Concrete cisterns are an excellent choice for non-potable harvesting of such runoff. A home can qualify for 4 points when an exterior collection system is large enough to hold run-off of at least 75% of the roof area of the house from a 1” rainwater event, and an additional one point if graywater is harvested on site and reused within the house.
EA – Energy and Atmosphere
EA-1.1 Optimize Energy Performance
At a minimum, LEED H requires houses to meet the requirements of an Energy Star home, 15% more energy efficient than home built to the requirements of the 2004 International Energy Conservation Code, (IECC). To earn Energy and Atmosphere credits, a home must exceed these minimum requirements. Between 2 and 34 LEED H points can be awarded based on the demonstrated energy efficiency of the house by building to exceed Energy Star performance requirements or by following prescriptive requirements of the various EA sub-categories pertaining to energy performance.
Concrete homebuilding systems are energy efficient because of their unique ability to combine high R-values, very low air infiltration, and thermal mass benefits in the exterior walls. To fully capture these benefits designers and builders should follow the LEED H performance requirements with a modeling program that will adequately measure and credit thermal mass benefits. Unlike wood or steel frame systems, concrete construction is largely continuous, with far fewer joints and seams, resulting in tighter construction. Finally, the concrete itself absorbs and stores heat energy, delaying the impact of exterior temperatures on the interior environment, which reduces heating and cooling loads.
EA 2 Insulation and EA 3 Air Infiltration
With wood and steel framing, careful attention must be paid to the elaborate installation of insulation and air barriers and their placement behind tubs, showers, fireplaces, and staircases. With the inherent continuity of insulation and air barrier in concrete wall systems, these time consuming difficulties are eliminated. The on-site detailing is simpler, requiring less skilled labor than with stick built construction. Required LEED H inspection procedures become less demanding with concrete wall systems as well.
MR – Material and Resources
MR 1.5.b Off-Site Fabrication
To reduce construction waste, LEED H provides credits for panelized construction as an alternative to on-site framing. Four points are awarded for the use of modular, prefabricated construction systems for all principal building sections. Panelized concrete wall, floor, and roof systems can all be manufactured off site, then shipped to the job and craned into place quickly, with minimal site disturbance, and no waste. Other site built concrete systems can be effectively managed during installation to greatly reduce the amount of debris generated in contrast to conventional frame construction. Points for these site built systems can be obtained by submitting a credit interpretation to USGBC demonstrating the comparative amounts of framing materials saved, the reduced number and size of thermal breaks, and the increased amounts of insulation.
MR 2.2 Environmentally Preferable Materials
The combination of recycled content, low emissions, and locally derived materials available with many concrete products can contribute to multiple points for a typical LEED H project. Table 24 of the system outlines where suitable environmentally preferable products can be used within a LEED home. In order to contribute, concrete used in exterior walls and foundations must contain at least 30% industrial by products such as fly ash or slag cement. Fiber cement siding, concrete masonry, patios, countertops, and roof tiles containing recycled materials all garner points as well as the use of sealed concrete floors. All of the above concrete technologies can also apply toward additional credit if they meet the LEED for Homes requirements for locally derived materials.
MR 3.2 Construction Waste Reduction
Debris from a variety of concrete products used in construction can be diverted from landfills and recycled. Concrete products and ready mix concrete are delivered to the site in the quantity needed, resulting in less site waste than frame construction. Any excess concrete is frequently collected, crushed and used as base material or fill. The foam from insulating concrete form systems can be collected and reground and reused in new foam applications. By reducing the amount of wasted materials, these systems will contribute to up to 3 points available for this category.
EQ – Indoor Environmental Quality
EQ 1 Energy Star with Indoor Air Package
A concrete home building project can contribute to 13 LEED H credits by complying with the various requirements of the Environmental Protection Agency’s, (EPA’s) Indoor Air Package. These requirements include a durable exterior envelope, one with strength, longevity, and effective interior and exterior moisture control capability and resistance. Previously discussed benefits like control of air infiltration, non-toxic pest control measures, and low VOC finishes like sealed concrete floors are all critical components to improved indoor air quality as well.
By using concrete systems and finishes, homebuilders and designers can more easily achieve LEED H certification for their homes. Whether through contribution based on the resource categories outlined in this article, or through accepted submissions for sustainable innovation credits, a concrete home provides the long term, high quality residential performance the USGBC is striving to encourage with LEED for Homes.
The information presented in this article is intended to highlight and summarize the ways concrete can contribute to the ability of a home to qualify for points under LEED for Homes. The reader should consult the latest version of LEED H directly for specific compliance requirements. More detail can be found at the US Green Building Council Site, www.usgbc.org. For more information on cement and sustainability visit the Concrete Thinker site at www.concretethinker.com.