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Fastening DensDeck Roof Boards

BrandonS | Posted in General Questions on

What is the best way to fasten densdeck through 4″ rigid foam on 1:12 roof with adhered TPO? My roofer is concerned the traditional screws and washers on top of the densdeck will be visible and a wear point under the TPO membrane.

The existing roof is a 1:12 gable roof with 1/2″ plywood decking.  We’re going to ice and water the entire roof.  Adhered ice and water seems to be the cheapest air barrier.  Over that, two 2″ layers of polyiso then the densdeck and fully adhered 60-mil TPO.

Thanks,
Brandon

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Replies

  1. user-5574861 | | #1

    Brandon,

    I had the same concerns as your roofer so we adhered the DensDeck to the polyiso and then adhered the TPO to the DensDeck. This stack up is an approved assembly by GAF who was the manufacturer of the TPO we used (75mil fleece backed extreme). They have different adhesives for different materials (fleece vs non-fleece, regular DensDeck vs Plus) so just need to make sure you get the correct one for each layer. If you live in a very windy area or have certain uplift criteria you need to meet, you may want to confirm with the technical support folks at the TPO manufacturer.

    1. BrandonS | | #2

      Thank you! My ultimate design wind speed is 115MPH and wind exposure category C. I will look into that.

  2. BrandonS | | #3

    Jonathan, thanks again. I was able to reach out to Mule Hide and their technical department was extremely helpful. The wind design requirements were calculated to 30psf uplift and they recommended their Helix foam adhesive with 12" attachment pattern on field and 6" on edges. They even provided a fastener pattern for the iso board and it was less than what I expected.

  3. user-5574861 | | #4

    Brandon,

    Glad to hear that Mule Hide was responsive and that this assembly will work for you.

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