Model building and energy codes are slowly increasing required levels of insulation in exterior walls, foundations and roofing assemblies. The NRCA analysis looked at how tougher energy codes affect a hypothetical 10,000-square-foot, single-story building in cities representing all eight U.S. climate zones. Construction cost increases and corresponding energy savings were developed by bumping up roof insulation in each city from R-10 to R-15, from R-15 to R-20, from R-20 to R-25, and from R-25 to R-30. How long it took to pay back the extra costs of the insulation varied by the city's climate and heating and cooling costs. The fastest payback, between 12.4 years and 13.3 years, was for an increase from R-10 to R-15. Some of the payback periods were very long -- 109 years for increasing the roof insulation from R25 to R-30 in Dallas, for example -- while the average life span for a low-slope roof is 17.4 years. The NRCA analysis concludes that R-value increases that result in cost payback lengths exceeding the anticipated life span of the roof aren't financially justifiable to building owners. But as heating and cooling energy costs increase, payback periods will get shorter. While thermal performance is important, the analysis said, the high R-value requirements of model energy codes don't give building owners and operators enough savings to justify the added expense. The NRCA recommends roof assemblies with the minimum required insulation in the jurisdiction where the building is located.
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