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Closed Cell Spray foam use on interior of corrugated metal roofing

lesleyjanice | Posted in General Questions on

We have a poorly constructed metal roof over two bedrooms in our house in the mountains in Colorado. It sits below a newly installed Trex deck, which we don’t want to pull up to solve the waterproofing and insulation problem below it. There is no way to access this roofing from above. The roof leaks and was not laid with sufficient overlap. There is also an area where the roofing slopes in a different direction and where these meet the conjunction is not level and problematic for waterproofing as well. The rooms had a dropped tile ceiling with pink faced fiberglass insulation, which we would pull off.. We are considering using closed cell spray foam and having a professional company apply this directly to the bottom of the corrugated metal roofing to insulate and waterproof this mess. We don’t plan to reinstall the ceiling tile. Temperatures can drop as low as -20F in the winter and get up to about 80F in the summer. Is this likely to solve the waterproofing problem? Will it adhere to the metal? Is it safe chemically to have it function as a bedroom ceiling once installed? Is it possible to find this product in a cream color so it isn’t so ugly as it is unlikely that we could find a way to install a ceiling below it. ¬†Thanks for any guidance, Lesley

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  1. woodguyatl | | #1

    You need a thermal barrier over the foam. I suspect you would need to first use dc315 or similar then a color of your choosing on top.

  2. Expert Member
    PETER Engle | | #2

    Your approach is very unlikely to fix a waterproofing problem. If the roof leaks, the only reliable way to fix it is from above, as difficult as it may be to tear up the deck and other overlying materials.

    As mentioned above, spray foam cannot be the ceiling material. You need some sore of fire barrier. Typically, this is 1/2" drywall, but there are special paints and other materials that can be acceptable. Once you spray foam, it will be difficult to tell whether the roof is leaking or not and any wet wood framing will be subject to rapid decay.

  3. Expert Member
    BILL WICHERS | | #3

    I wouldn't trust spray foam as a water proofing material here. What would likely happen is that the leak would pool above the spray foam and gradually cause sections of the foam to seperate and fail. You'll need a fire barrier on the inside as other have mentioned too.

    I would check with a commercial roofing contractor and see if they have any ideas. Commercial flat roofs have more sealing issues than the typical residential roof, so a commerical contractor may have a better idea what products might work in your application. You're probably going to need to pull up at least a few planks of your deck to fix this roof.


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