Concrete Wall Systems Can Assist with a Tight Thermal Envelope|
Building an Energy Star® rated home needs to start with the building envelope. As sustainable building becomes more prominent and building codes more stringent, contractors are seeking information and assistance in achieving Energy Star® compliance. For many builders, constructing with concrete can be an easier way to meet new higher energy benchmarks and even help meet the qualifications for government tax incentives.
The federal Environmental Protection Agency (EPA) and Department of Energy introduced Energy Star home certification program to ensure that new, qualified houses are built to higher performance standards. Homes built to meet Energy Star ratings can be 15% more energy efficient than the requirements of the current International Residential Code and include additional energy-saving features, often making them more efficient than conventional residential construction.
The EPA recognizes how much the careful construction of the exterior envelope can improve the overall energy efficiency of a home. For that reason, a Thermal Bypass Checklist must be completed for all homes that wish to earn the Energy Star Label. The Thermal Bypass Checklist was developed to provide builders and inspectors with a comprehensive list of critical frame construction details that must be employed to make sure improper workmanship has not compromised the thermal performance of the exterior wall assembly.
Thermal bypass refers to the movement of heat around and through insulation. For insulation to be an effective thermal barrier, it must be combined with an air barrier — material that restricts the flow of air through the wall assembly. Both must be installed without any holes, gaps, voids, compression, or wind intrusion. Creating just a 5% gap in insulation coverage reduces the effective R-value by 50%, leaving little room for installation error.
Conventional insulation products work by trapping air. Allowing air flow through insulation reduces its effectiveness. This can occur in conventional frame construction when thermal blankets — called batts — are installed in the open spaces between framing members. If the insulation is not carefully installed tightly on all sides up against surrounding air barriers, framing, and finishes, or if it is compressed around electrical wiring, pipes, or other obstructions within the wall, the thermal performance of the wall can suffer.
The Thermal Bypass Checklist identifies these details and also indicates which features third-party energy inspectors must verify.
There is another choice for builders. Properly installed continuous concrete and foam wall systems, such as insulating concrete forms (ICFs) can provide alignment of insulation and air barriers with no gaps, voids or compression. This can provide the homebuilder with a greatly simplified thermal assembly. Concrete wall systems can obtain a tight thermal envelope with fewer contractors than conventionally insulated frame construction.
The Concrete Home Building Council (CHBC) of NAHB offers two educational courses aimed at helping attendees learn about the application and installation of ICFs through the Home Builders Institute (HBI). “Building with Insulating Concrete Forms” is an eight hour course that provides the traditional homebuilder with the information needed to evaluate and start using ICFs. “Insulating Concrete Forms Installation” is a one or two day course that provides students with thorough information and basic skills in the correct construction of walls using insulating concrete forms. More information on these two courses is available on the HBI Web site, www.hbi.org. There is more information available about ICFs on the CHBC Web site, www.nahb.org/concrete or from the Portland Cement Association, www.cement.org.
EPA’s Thermal Bypass Checklist Guide indicates air barriers “must be perfectly aligned with the insulation” in order for conventionally built wall assemblies to insulate properly. Wall Section 1 shows a cross section of a typical two-story wood frame exterior wall with batt insulation. It identifies the potential trouble spots identified in the Checklist that have to be carefully handled by the builder, and reviewed by the energy raters.
Wall Section 2 shows a two-story ICF exterior wall section assembly. This assembly has fewer areas requiring special consideration and inspection. Building with ICFs, removable forms, precast concrete, or similar concrete and foam systems can eliminate critical coordination issues and construction details that would have to be addressed and verified when building typical Energy Star-compliant exterior walls. This saves valuable time and allows high performance concrete homes to be completed quickly.
Achieving an Energy Star rating isn’t only environmentally beneficial, it makes financial sense. Many local governments and utility companies offer incentives for energy savings. Often these programs will provide incentives for energy efficiency that meets the equivalent of the Energy Star requirements. Information on these opportunities can be found at www.dsireusa.org.
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