A.Corresponding editor Paul Fisette responds: Some vinyl siding manufacturers void their warranty for heat distortion when their siding is installed over foil-faced foam. One study has shown that when vinyl siding is installed over foil-faced foam, the temperature of the back of the siding can be 8°F warmer than when it’s installed over foam without foil. Installers who are concerned about heat buildup should select rigid foam without foil facing.

Nevertheless, some manufacturers have no objection to the installation of vinyl siding over foil-faced foam. Whenever vinyl siding is installed over rigid foam (with or without foil facing), studs should be spaced no more than 16 inches on-center, and the thickness of the foam should be limited to 1 inch. Because rigid foam doesn’t provide much...

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