CMU walls and rigid foam
Bbrown3381
| Posted in GBA Pro Help on
Retrofit concrete block walls painted inside and out. Exterior foam then rainscreen then siding. Keeping painted block as interior walls.
Do I have to be concerned with the vapor permanence of the foam?
Also, would there be any benefit in using foil faced…other than R-value?
Southern Georgia coast.
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Replies
Robert,
Q. "Do I have to be concerned with the vapor permanence of the foam?"
A. No.
Q. "Would there be any benefit in using foil faced...other than R value?"
A. The foil facing would add about R-1 or R-2 to the assembly if it faces a rainscreen gap. Foil facing makes it easier to tape the seams of the rigid foam, which may be an important consideration if you intend to use the rigid foam as a water-resistive barrier (WRB).
Just out of interest....do I need a WRB with painted block behind the rigid foam.
Robert,
Every wall needs a WRB. A WRB is required by code and strongly recommended by construction experts.
One reason that you need to have a WRB is so that you know how your window flashing will integrate with your WRB. The WRB and the window flashing are part of a water management system.
Homes with concrete block (CMU) walls often have liquid-appplied WRBs. For more on liquid-applied WRBs, see these two articles:
Housewrap in a Can: Liquid-Applied WRBs
Liquid-Applied Flashing