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Cross use of building materials

user-669103 | Posted in Green Building Techniques on

While re-roofing I’m going to have to take the vinyl siding off a dormer to lap flashing up the wall as high as the snow line. While I am at it I plan to re-flash 3 windows on the dormer.

From the roofing work I will have about 5 sq of Grace Tri-flex breathable membrane spare, and some Grace Ice & Water or Grace Ultra.

Q> Should I use left over Grace Tri-Flex as an alternative to house wrap (e.g. Tyvek) on the dormer?
Q> I presume that I should remove the tar paper first no mater what I use?
Q> For the Window re-flashing can I use left over Grace Ice and Water or Ultra instead of Grace Vycor.

Grace Tri-flex: 0.54 perms
Tyvek: 54 perms
I think that the Tri-flex is stronger and let’s less water pass, but is less permeable and does not stand up to UV as well (which is not an issue).
I’m surprised that the Tri-Flex is not more permeable.

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  1. user-669103 | | #1

    If I used GAF Deck Guard instead of Grace Tri-Flex that would have a permeability of 16 perms.
    So using GAF Desk Guard left overs of that instead of Tyvek or other house wrap might be better.

    Anyway the question still stands.
    Since tar paper used to be used for both walls and roofs, maybe this is okay?

    My aim is to avoid having wasted materials -- un-green, and save a few $.

  2. GBA Editor
    Martin Holladay | | #2

    You are mistaken when you write that Grace Tri-Glex is a "breathable membrane." Since its permeance is 0.54 perm, it falls into a category that Joe Lstiburek calls a "Class II vapor barrier." It meets all code requirements for vapor retarders.

    Grace Tri-Flex is specified whenever one needs a roofing underlayment that doesn't breathe. For example, inward solar vapor drive can be a problem with some cathedral-ceiling roofs with asphalt shingles. To stop inward solar vapor drive, you need a roofing underlayment that is NOT vapor permeable. You can't use asphalt felt. The solution is Grace Tri-Flex.

    Since Grace Tri-Flex is a vapor barrier, it is NOT a substitute for Tyvek, which is vapor permeable.

  3. GBA Editor
    MIKE GUERTIN | | #3

    Q1 - TriFlex or housewrap: I asked Grace about this and their answer is 'NO.' Primarily due to very low permeability. From a building science standpoint the answer is 'it depends.' Depends on your climate, potential to leaks from outside, moisture vapor drive from inside and the wall construction profile. In general, if you use TriFlex as a housewrap you want a wall profile that will be able to 'dry' to the inside since there isn't too much drying potential through TriFlex.

    Q2 Old tar paper has holes in it no doubt so you can't reuse it. You could leave it however and just apply another sheet of tar paper over it.

    Q3 Definitely can use Ice and Water as flashing tape: Grace watched us cutting strips of Ice and Water Shield to use as window flashing tape and developed Vycor.

    Other uses for left-overs:
    Ice and Water Shield - if you weren't already planning to, you can run a strip of Ice and Water Shield on the roof to wall connections (cheek wall, face wall). 9 in. on wall and 5 to 7 in. on the roof or more if you want. Save left overs to use as emergency patches on kayaks and canoes after a rough class V run, hose leaks, or your next window install.

    TriFlex - actually makes a pretty good roofing material for sheds. I've got a TriFlex 'roof' on mine thats' going on 3 years old. Still waiting for some left over roofing. 2 in. strips of TriFlex make great deck joist caps before laying down decking or isolation membrane between ACQ lumber and metal hardware. It works great in place of poly or EPDM as a sub-grade foundation drain too as in this detail:

  4. user-669103 | | #4

    What about GAF's Deck Armor ...

    Thanks guys. I think I was being a little dumb, since I know full well that 0.54 perms is about the same as 2" of XPS and that's a vapor retarder (class II). My brain must have been too tired (I posted the question at something like 3am).

    After hopefully better applying my brain this time I'm going to use GAF's Deck Armor for those parts of the roof that need to breath. This has a permeability of 16 perms (compare with Tyvek products which are in the range 20 to 54 perms).

    However, I will still have about 6 sq left off a 10 sq roll.
    So I'm thinking of using GAF Deck Armor instead of Tyvek.

    If I don't hear from you, in answer to this I'll call GAF and see if I can get a confident answer to post back myself.

    I may have left over TPO as well - already thought of a use for that -- pond liner.

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