Which is best for an attic: closed or open cell spray foam?

Asked by Karen
Zebulon, NC

I am not talking about walls. It is an unfinished attic. I am concerned that if we get a leak we will be unable to find it. My husband feels that closed cell is the best product for keeping our home warm. I am hearing that the difference is not that significant since we live in North Carolina where it does not get that cold.


Matthew McCullough

Answered by Matthew McCullough

Stamford, CT

The Green Insulation Company

February 22, 2011

Closed cell in an attic (sprayed on the roof deck) is not always the best idea.

In your climate zone, you can use open cell foam and save the money for something else.

  • With open cell, if you have a roof leak it will eventually drip into the house and you will be able to pinpoint where the leak is on the roof and fix it.
  • With closed cell the foam will prevent the water coming into the house, but will not stop the leak from saturating the plywood under the shingles, which eventually will cause it to rot out and cause much larger problems in the future.


For more information:

Read "Should we insulate the attic of our 1926 bungalow with spray foam insulation?" a Q&A answered by Anthony Addesso.

Also, read "I'm converting my attic into a non-vented conditioned space. Should I use open cell or closed cell foam to insulate?" a Q&A answered by Steve Saunders.

Tagged In: spray foam, attic insulation

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