Foam insulation over shingles?


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Old 06-05-08, 06:14 PM
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Foam insulation over shingles?

I have an old house that has wooden shingles attached to the original clapboard; the shingles were originally stained, then primed and painted sevaral years ago.

Many are currently in bad shape (some are curling up, others falling out). I was thinking of putting foam insulation on them then nailing shiplap boards over the foam, then staining the shiplap. The house contains blown-in insulation already, but I want to insulate further.

Some people say that I should not put the foam insulation over the shingles because it may cause moisture problems, but the shiplap boards will be okay. Others disagree, and some say I must strip off the shingles. However, I'd like to avoid doing that. Will it be okay to attach both the foam and shiplap, or just the shiplap over the shingles?

Thanks for your time.
 
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Old 06-05-08, 06:46 PM
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Closed cell foam will be a moisture barrier! It will cause problems.
 
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Old 06-06-08, 09:55 PM
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Yea, if you put foam over the top it will be a moisture barrier and condensation will form there and attack the bottom of you new shiplap board.

Just put the shiplap over the shingles, then ice and water shield and then the roofing materials.
 
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Old 06-07-08, 05:05 AM
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Putting anything over the existing shingles without tearing them off first is bad advice since you already mentioned they are curling up. Tear off the shingles first!

If you want more insulation, then blow more cellulose into the attic, or if you can't get enough r-value that way, remove the cellulose and spray foam the space instead, since spray foam has better r-value per inch.
 
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Old 06-08-08, 06:54 PM
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Thanks for your help. What would be sufficient for ice and water shield?

Originally Posted by adambeazley
Yea, if you put foam over the top it will be a moisture barrier and condensation will form there and attack the bottom of you new shiplap board.

Just put the shiplap over the shingles, then ice and water shield and then the roofing materials.
 
 

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