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Community and Q&A

Smart Membrane for Roof

EhvC | Posted in Energy Efficiency and Durability on

I was just informed that SIGA does not have a acrylic membrane that is designed to go on a roof (only walls). Anyone have a suggestion which acrylic membrane would work best for my roof? It will be placed on top of pine t&g boards.



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  1. Expert Member
    Akos | | #1

    There are also a number of roof membranes with butyl adhesive that will work such as Grace HT or FT platinum HT-sa.

    I've used VP100 for a small roof section. It is not rated for roof but works well enough but won't hold up to a lot of foot traffic.

    1. EhvC | | #2

      thank you, I will check it out

  2. Expert Member
    Michael Maines | | #3

    By "acrylic membrane" do you mean a self-adhered membrane? I'm not aware of any membranes made using acrylic other than as the adhesive. Siga Majcoat is intended for roofs. It's not self-adhered but you can easily tape the seams to make it airtight if that's your goal.

    1. EhvC | | #8

      Yes, a glue that doesn’t react with pine boards or smell bad.

  3. GBA Editor
    Kiley Jacques | | #4

    I’m assuming the membrane is for vapor and possibly air control too. Take a look at this lineup of products: Smart Vapor Retarders, as well as this article: Smart Vapor Retarders for Walls and Roofs .

  4. Expert Member
    PETER Engle | | #5

    I wouldn't be too concerned about the wall/roof thing in your case. You are putting the membrane on the conditioned side of the insulation stackup, so it won't see typical roof temperature swings. SIGA is probably concerned about people using it as a roofing underlayment, which would be a bad idea. On top of your T&G, it'll work fine, though probably still would void manufacturer's warranty if that's a concern for you.

    1. EhvC | | #9

      I agree but I am also looking at putting the membrane directly on the plywood underneath the steel roof instead of on the pine boards.
      If I put a membrane on the pine boards, I would also need to put some kind of a membrane underneath the steel roof to keep water out.

  5. the74impala | | #6

    Roof or Ceiling?

    1. EhvC | | #10

      It is a sandwich of pine boards and insulation panels covered by a vented steel roof

  6. pnwnerd | | #7

    Why acrylic specifically? What are your requirements?

    1. EhvC | | #11

      Some adhesives react with pine (pitch) and could also smell bad for quite awhile

  7. Expert Member
    Akos | | #12

    With T&G you need a warm side air and vapor barrier. The peel and stick over the pine will seal up everything up nicely, so the air barrier is taken care of. Most acrylic peel and sticks are vapor open, as long as you have rigid foam right above it, the rigid will act as a vapor barrier.

    In case of the a membrane with butyl adhesive, the membrane will act as both air and vapor barrier. The permeability of the rigid over that stack up doesn't matter any more. Permeable and non-permeable rigid will work just fine.

    For the final underlayment under the metal, you can use any of the standard synthetic roofing underlayments. I prefer to use a permeable product as it allows for the roof deck to dry in case any water makes it in there. This is stock item at my local roofing supply and the extra cost is minimal.

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