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AC_Hacker · 01-31-12, 06:34 PM

There is another approach to this insulating problem...

A hybrid system, where closed-cell foam is utilized, next to the weather side, for it's better R-value, and also for it's exceptional air sealing qualities. Also used in this system is cellulose, next to the living space side... where it's R3.8/inch provides insulation at a lower cost than closed-cell foam.

There is controversy with such a system, because as moisture-laden air is migrating through the cellulose part of the declining temperature gradient, the possibility exists that the dew point might be reached in the cellulose layer, thus dropping moisture within the wall (or roof).

The fix is to make the closed-cell foam layer thick enough that the moist air will be immobilized before it reaches the dew point.

The last word on this issue seems to be this document.

-AC_Hacker

01-31-12, 06:34 PM	#20
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	There is another approach to this insulating problem... A hybrid system, where closed-cell foam is utilized, next to the weather side, for it's better R-value, and also for it's exceptional air sealing qualities. Also used in this system is cellulose, next to the living space side... where it's R3.8/inch provides insulation at a lower cost than closed-cell foam. There is controversy with such a system, because as moisture-laden air is migrating through the cellulose part of the declining temperature gradient, the possibility exists that the dew point might be reached in the cellulose layer, thus dropping moisture within the wall (or roof). Discussion here Discussion here Discussion here The fix is to make the closed-cell foam layer thick enough that the moist air will be immobilized before it reaches the dew point. The last word on this issue seems to be this document. -AC_Hacker __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker...