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Roofing underlayment for 2:12 standing seam metal roof

Joe Norm | Posted in General Questions on

I inquired here a week or so ago about this same question but still remain a little unclear.

I was told by a local roofing contractor to apply a fully adhered membrane to my 2:12 sloped shed roof. 

The insurance of no leaks is appealing, but the material is also very expensive. My question is whether or not it is necessary. Tyvek Protec, and others say their synthetic(non fully adhered) is good to 2:12 and they’re much less expensive.

The roof has no dormers or valleys just a straight shot, but some of the panels will be about 37 feet long, so not a short run.

thanks

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Replies

  1. Expert Member
    Malcolm Taylor | | #1

    Sorry Joe - I've forgotten: The roof is snap-lock metal panels?

    1. Joe Norm | | #3

      Malcom,

      Originally yes, but the most common panel from the two manufactures I deal with recommend a 3:12 at minimum. There is a more expensive panel (one with floating clips) that can do 2:12.

      My question is whether to put down peel and stick and then disregard the recommendation odf the roof pitch, or to use a more standard underlayment with a panel rated to 2:12 pitch?

      I have leaned many things through the design and build(so far) of this place, one is to not use a low slope roof. But I am here now so I have to come up with something. Thanks

      1. GBA Editor
        Brian Pontolilo | | #5

        Hey Joe,

        What are you trying to gain here? Cost savings? In other words, why would you not go with the manufacturers recommended panels and their recommended underlayment for use with that panel?

  2. Expert Member
    Akos | | #2

    Joe,

    I would call the manufacturer. When I was looking for 2.5/12 slope panels, most of them were fine with using their 3/12 panels over peel and stick.

    With such long runs, there will be some decent thermal expansion (order of 3/8" to 1/2"). Make sure the installers are dealing with it properly and if you are in snow country, they don't pin the panel at the eaves by accident with snow retention clips.

    1. Joe Norm | | #4

      Thank You,

      Yes, with such long panels I was wondering if using a panel type with the floating clips is a better way to go? Most of those are rated for lower pitch anyway. I am not in snow country and I will be the installer. Thanks

      1. Expert Member
        Akos | | #8

        I would get panels rated for 2/12. For extra piece of mind, you can run a layer of peel and stick say 6 feet up from the eaves.

        Most panel designs can handle a decent amount of thermal expansion, you just have to check how much your install can expand and make sure the slots on it can provide enough float.

  3. Kevin Spellman | | #6

    I had the exact same pitch and length to my roof. The roofers would not warranty the work without high temperature peel and stick underlayment. They also would only do mechanically seamed even though they said there are some snap locks available.

  4. Nathan Scaglione | | #7

    Joe it seems like your gut is telling you the right thing: Don't install a manufacturer recommended 3/12 or steeper roof on a 2/12 slope.

  5. Joe Norm | | #9

    I will go with the 2:12 rated panel.

    But.......do I still need peel and stick or will regular underlayment be OK? Most that I see are rated for 2:12

    1. Expert Member
      Malcolm Taylor | | #10

      Unless your roofing manufacturer says otherwise, you can use any synthetic underlayment for your roof.

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