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Community and Q&A

Taping overlaps in roof vapor barrier?

Hari Kamboji | Posted in General Questions on

I’m adding insulation to the exterior of my roof. The stack will be as follows, from bottom to top:

5.5 inch Roxul in rafter bays (underside of roof)
existing sheathing
vapor barrier (solitex mento)
3 inch poly iso
4.5 inch nailbase (Hunter panels: 3 inch poly iso, 1 inch vent gap, .5 inch osb)

Today the roofers came to start- they removed old shingles and put down the vapor barrier.
However, they did not tape the overlaps between layers of the vapor barrier. I mentioned it since I thought I’d heard it should be done, but the foreman didn’t seem to think it was necessary and didn’t seem familiar with the practice. Should I insist? If so, suggestions on what kind of tape should be used (something easily available at hardware store)?

Thanks so much,

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    There are several issues here.

    First, Solitex Mento is not a vapor barrier. In fact, it is very vapor-permeable (rated at 38 perms). In this assembly, my guess is that its purpose is to act as an air barrier, not a vapor barrier.

    Inasmuch as it is supposed to be an air barrier, the seams of the Solitex Mento should certainly be taped. I advise you to contact 475 High Performance Building Supply -- the distributor that sells Solitex Mento -- and ask their advice on which tape to use.

    For more information on how to put together this type of roof assembly, see How to Install Rigid Foam On Top of Roof Sheathing.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Here is a link to the installation instructions for Solitex Mento.

    The tape you need to buy is Tescon Vana.

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Here is a link to a document from ProClima that also recommends the use of Tescon Vana tape.

    The document also notes that "The system components [include] TESCON NAIDEC nail sealing tape."
    It sounds like that is the product you need to seal nail penetrations.

  4. Hari Kamboji | | #4

    Thanks Martin!
    Yes air membrane- my mistake! I assumed that the roofers would have tape when I ordered it. Given that I don't think there is time to get Tescon Vana from 475 by tomorrow morning, do you think there is a reasonable substitute (Dow Weather Seal for example)?

    Also, I updated my previous response with a photo. Should I be concerned about the nailing of the membrane?

  5. User avatar GBA Editor
    Martin Holladay | | #5

    See my comments about nail-sealing tape in Comment #4.

    Don't rush the job. Buy the right tape.

  6. Hari Kamboji | | #6

    Thanks Martin-
    I think I missed your comment 4 while I was typing comment 5.
    I realy appreciate your quick responses. Kicking myself now for not seeing about the tape back in April when I ordered the membrane.

  7. Hari Kamboji | | #7

    By the way, it appears that the vapor barrier was attached to the decking with nails (you know, the kind with the bright orange ring, that you use to fasten insulation). Not just along the rake, but all across the roof. Is this OK? I ask because intuitively, piercing the membrane to secure it introduces punctures that might defeat the purpose of the membrane. See the photo.

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