January 2007

Saving energy with spray foam

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by Mark Bomberg and Mason Knowles
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Building codes require minimum R-values for all buildings, and the codes typically provide a prescriptive table that details the R-values required for specific climate zones. However, the R-values listed are based on laboratory test procedures and do not take into consideration field performance of insulation. Seldom does insulation perform in the laboratory as it does in the field, but advances in building-envelope technology and test procedures have given roofing professionals an opportunity to address many factors that can contribute to the total energy performances of building systems.

One example of this is spray polyure­thane foam (SPF). During the past 30 years, a great deal of scientific research has been conducted to identify factors other than R-value that affect thermal performances of roof and insulation systems. The Spray Polyurethane Foam Alliance (SPFA) has been active in promulgating research to put real numbers behind these concepts. During the past two years, SPFA has conducted thermal performance research in attics and wall assemblies with coordination and input from Oak Ridge National Laboratories (ORNL), Oak Ridge, Tenn.; R&D Services, Cookeville, Tenn.; National Association of Home Builders' Research Center; Syracuse University, Syracuse, N.Y.; and Architectural Testing Inc., York, Pa.

During the summer of 2006, SPFA asked Mark Bomberg, a building scientist at Syracuse University and principal of TI Research, a consulting company in Syracuse, to analyze the relative energy performances of SPF roof systems. The goals of the research were to evaluate the factors affecting energy performances of SPF roof systems in the field, review existing data from building-envelope research that relates to these factors, and develop a matrix that could be used by contractors to provide a more accurate estimate of the effective field performances of SPF roof systems in various climates and building scenarios.

The research also reviewed published scientific papers about the factors that affect thermal performances of roofing materials, including thermal drift (aging of gas-filled foam insulation), thermal bridges created by mechanical fasteners, effects of air movement on energy performance and moisture gains in roofs, and reduction of surface temperature on cool...

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