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Insulating a porch ceiling

I have a small ranch with one corner of the house with a 9x13 covered porch. The ceiling of the porch is osb painted with exterior latex. The attic above is insulated up to the exterior walls of the porch but not over porch. I would like to add sheathing above the porch area for storage but wonder if I should insulate first. Also am concerned about moisture. Live in NW PA with harsh winters and we grill and smoke year round on the porch which could add heat and moisture to the porch ceiling.Thought about sealing all seams of the porch ceiling and insulating before adding decking. Or should I just add the decking without any insulation? What is the best for energy efficiency?

Asked by J. Gaub
Posted Nov 6, 2010 9:30 PM ET
Edited Nov 7, 2010 7:02 AM ET


2 Answers

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Insulation needs to extend only to the outer walls of the conditioned space, not over an unconditioned porch. However, if you're creating lots of moisture under the porch roof, and that roof is continuous with the house roof, then you should have continuous soffit and ridge ventilation to evacuate any moisture that gets into the attic (but no intake vents in the porch area).

Answered by Riversong
Posted Nov 6, 2010 10:26 PM ET


If I understand you correctly, your attic extends over conditioned space (your house) as well as over unconditioned space (your porch).

Although you are worried about moisture, I think that's the wrong worry. You need to be worried about air barrier integrity.

You need to get up in your attic and look at the region of your attic where the attic insulation stops and the porch ceiling begins. Examine the perimeter top plates and be sure that the builder had a plan to ensure air barrier integrity. Also check to be sure there are wind-washing blocks between the floor joists where the insulation stops. Any cracks in these areas need to be carefully air sealed. Spray foam may be useful in this area.

Answered by Martin Holladay, GBA Advisor
Posted Nov 7, 2010 7:02 AM ET

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