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MICHAEL RICE Posted: Nov 16, 2009 10:28 PM	sprayfoam 1inch or cavity fill? i have received a bid for spray foam and was told 1/2 lb for foundation walls is best as it allows any moisture that may enter to exit. asked about 2lb foam he stated i can use it but over 1inch is overkill. is any of this true. why not fill the cavity? i thought r10 was the energy star standard. is 2lb the appropriate weight for open (net yet closed) cavity?
mason Posted: Nov 18, 2009 06:35 AM	The thickness of foam is dependent on 3 factors, the economic thickness to provide energy performance relative to cost; the minimum thickness to prevent condensation; and the minimum thickness to comply with building codes. You would use the thickest of the 3 requirements. It varies from climate to climate. Check your building code tables for your area and go with the prescribed thickness. Or, obtain data that demonstrates you can use less and still provide the required energy and moisture control performance. (WUFI study or its equivalent and energy performance testing of assembly by a credible 3rd party source acceptable to the code official). As for using 1/2 lb or 2 lb, either can be used to insulate the inside of the foundation wall, but only use the closed cell foam for outside foundations. Depending on the climate the open cell foam may require a vapor retarder element added to the design (colder climates) while the closed cell foam is accepted by the codes as a class II vapor retarder and does not require additional vapor retarder elements, providing the thickness of the foam is sufficient to provide enough insulation to stop condensation. Again, use the table in the building code for that thickness.
Gerry Wagoner Posted: Nov 20, 2009 08:45 AM	Open cell foam is wholly undesirable in below- grade situations where saturation may occur. gcw

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MICHAEL RICE

Posted: Nov 16, 2009 10:28 PM

sprayfoam 1inch or cavity fill?

i have received a bid for spray foam and was told 1/2 lb for foundation walls is best as it allows any moisture that may enter to exit. asked about 2lb foam he stated i can use it but over 1inch is overkill. is any of this true. why not fill the cavity? i thought r10 was the energy star standard. is 2lb the appropriate weight for open (net yet closed) cavity?

mason

Posted: Nov 18, 2009 06:35 AM

The thickness of foam is dependent on 3 factors, the economic thickness to provide energy performance relative to cost; the minimum thickness to prevent condensation; and the minimum thickness to comply with building codes. You would use the thickest of the 3 requirements. It varies from climate to climate. Check your building code tables for your area and go with the prescribed thickness. Or, obtain data that demonstrates you can use less and still provide the required energy and moisture control performance. (WUFI study or its equivalent and energy performance testing of assembly by a credible 3rd party source acceptable to the code official).

As for using 1/2 lb or 2 lb, either can be used to insulate the inside of the foundation wall, but only use the closed cell foam for outside foundations. Depending on the climate the open cell foam may require a vapor retarder element added to the design (colder climates) while the closed cell foam is accepted by the codes as a class II vapor retarder and does not require additional vapor retarder elements, providing the thickness of the foam is sufficient to provide enough insulation to stop condensation. Again, use the table in the building code for that thickness.

Gerry Wagoner

Posted: Nov 20, 2009 08:45 AM

Open cell foam is wholly undesirable in below- grade situations where saturation may occur.

gcw

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