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Old 12-13-2010, 02:30 PM   #1
Join Date: Dec 2010
Location: PA - Philly Suburbs
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Insulation under attic AC unit

I have taken on the project of adding insulation to my attic.

I am adding another R-30 layer on top of my R-19. My attic is complicated, considering the AC unit (located on floor joists) and duct work (on floor joists) extend down much of the center (approx 95 sq ft). While I will be adding the R-30 throughout and close to the AC unit, I will not be able to fit any significant new height of insulation underneath the AC unit or ducts. R-30 is like 10" high. I probably have 4" underneath the unit.

So, I had the idea to use a 2" rigid insulation under the unit. Adding an additional R-10 at least. I learned that this is not safe with the fire hazard limitations of rigid foam. I thought about adding it only to the duct work areas - not AC radiant heat areas. I just hate to do the project but leave a huge area with only the R-19 in the middle. Is there a way of adding the rigid foam safely? I have read the drywall enclosure concept for walls, but this may be too difficult.

Could drywall glued on the foam be a legitimate safety precaution? Any suggestions? Thank you - Nick


Last edited by nickelshine; 12-20-2010 at 12:26 PM. Reason: no replies
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