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Community and Q&A

Opinions on Open-Cell Spray Foam on Flat Roof With Decking

jsnmckinney | Posted in General Questions on

Hello Community!

I’ve done a ton of research on the topic of Open Cell vs Closed Cell Insulation.  My wife and I recently went under contract on a new house and we are nearly at the point of walking away because the builder used Closed Cell on all exterior walls but Open Cell (10”)on the roof.  It is a flat roof with roof decking on top. There is NO vapor barrier installed. Our concern is that the roof plywood will eventually rot due to warm air traveling to the cold roof during the cold of winter.

This builder has fantastic reviews from all previous build and states he has done this on all builds for the last 10-15 years, but from how I understand it you may not know of an issue until you fall through the roof or when you go to replace the roof. I also spoke to the team whom installed the insulation and they state this is how they have done business on flat roofs for the last 10 years with “no issues”.

We live in Chicago (climate zone 5).

Questions for the community..

Are we crazy for walking away from the house?

Are there any recommendations we can take back to the builder for remediation?

If a vapor barrier is required, is there any way to install without ripping out all the ceilings?

Thank you!

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  1. Expert Member
    Akos | | #1

    How big is the roof?

    Open cell is not a great idea in Zone 5, you can read about this here:

    Your contractor could have saved a fair bit of money and also made the building much more robust by flipping where closed cell and open cell was applied. There is nothing wrong with using open cell foam in walls in any climate, closed cell foam always works for an unvented compact roof.

    Since the house is built already, the best is to apply a vapor barrier paint to the ceiling and hope for the best.

  2. jsnmckinney | | #2

    I verified with whom actually installed the insulation. Come to find out they did 10” of open cell in the inside attached to the roof plywood then r21 worth of closed cell on the outside then the roofing.

    I think we’re going to be okay after all.

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