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Need 2 foot square of vapor barrier

Jeremy M | Posted in Building Code Questions on

I’m planning to take out the 50s era milk chute in our house tomorrow. This will leave me with a whole between 12-20 inches square. I’ll put plywood of the same thickness and vinyl siding.

I’m fine on the vinyl siding and sheathing, plus a piece of fiberglass and then drywall. For all I have pieces of leftovers or can buy in small quantities.

I’m stuck on what goes between vinyl and sheathing. I don’t want to buy a huge roll of tyvek for such a small area. I need this for tomorrow, day after at the latest.

Ideas? Suggestions? Thanks!

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Replies

  1. Stephen Sheehy | | #1

    There must be somebody building a house nearby. Stop and ask if you can scrounge a scrap piece of housewrap or 15 lb. felt.

  2. Steve Knapp CZ 3A Georgia | | #2

    Most of the big box home improvement stores have scrap bins. These materials are usually free.

  3. Expert Member
    Dana Dorsett | | #3

    In most climates you don't need or want a vapor barrier on the exterior OR the interior. On the exterior what you're looking for is a weather resistant barrier (WRB), and it has to be lapped properly with the WRB for the rest of the wall such that bulk water sprayed onto it is always directed to the exterior as it runs down the wall.

    In US climate zones 6 or higher code requires a Class-II or Class-I (= vapor barrier) vapor retarder on the interior side of the assembly, but "vapror barrier latex" primer on wallboard is good enough for the interior side, as is half-inch CDX plywood or half-inch OSB (unpainted or painted), either of which is a Class-II vapor retarder when dry.

  4. Jeremy M | | #4

    Thanks all. I'm near Cleveland, OH. I put a "in search of" on a FB buy-sell group but so far no luck. I still need to buy the siding at Lowes, I'll ask. If I can't find any than I'll try to figure something else out. Nothing? Tyvex tape?

  5. Expert Member
    Dana Dorsett | | #5

    In Cleveland (US climate zone 5), with vinyl siding on the exterior code does not require an interior side vapor retarder any tighter than standard latex paint on wallboard.

  6. Brendan Albano | | #6

    You can buy small quantities of tyvek from Amazon (no doubt at a large markup, but in terms of total dollars it's still cheap). Maybe time to get an Amazon Prime account ;)

    You can also buy it by the foot here: https://www.antigravitygear.com/shop/shelters-accessories/tyvek-ground-cloth-by-the-foot/ but the shipping probably isn't fast enough. (It's popular for budget DIY camping gear, although part of the budget part comes from scavenging it from construction types).

    As everyone else has commented, it's the "weather resistant barrier" that you are talking about between the sheathing and the siding, not a vapor barrier.

  7. Charlie Sullivan | | #7

    If your schedule is flexible enough to accommodate the shipping schedule of the source Brendan posted, that's ideal. Another possibility that might or might not be a good idea is to go to a post office or a office-supply store and get a Tyvek envelope. The post office seems to offer 12x15 envelopes at no charge. You could unfold it to 24x15. The post-office doesn't list a perm rating, so I'm not sure it's the same stuff, but it is Tyvek brand, and if the schedule does not allow getting something you are sure of, that could be an option.

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