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Access panel for plumbing- can it be a vapor barrier?

Lis77 | Posted in General Questions on

I have a tile shower and am putting an access panel to the shower’s plumbing over the stud bay in the closet on the other side of the wall. I want to make it the full width and almost the full height of the stud bay. My question is, what kind of materials is it okay to use for the panel? If I use something that is impervious to moisture, will I trap moisture in the wall?

Secondly, the closet is not heated, should I put a layer of insulation over the plumbing?

I am in the pacific northwest.

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  1. Expert Member
    BILL WICHERS | | #1

    Is this an interior or an exterior wall?


  2. Lis77 | | #2

    Thanks, Bill. This is an interior wall. The tile shower is on one side of the wall and the bedroom closet is on the other side, with the plumbing in that wall.

  3. Lis77 | | #3

    Do pipes sweat inside of walls at all? Or only when they are out in the open?

  4. Expert Member
    BILL WICHERS | | #4

    Moisture accumulation isn’t really an issue in interior walls since you don’t have a cold, condensing surface the way you do on the outside surface of an exterior wall. Because of this, there is no need for things like vapor barriers on interior walls. You can make your access panel out of whatever material is handy, although plywood is probably the most common material to use. I’d use sanded plywood with an A grade face veneer, primarily to give you an easy surface to paint so that it will look good.

    Pipes most certainly CAN sweat inside of a wall. All you need is for the pipe’s temperature to be below the dew point of the air in the wall, and with interior walls that air will be pretty much the same as the air in the house. If you want to prevent the pipes from sweating, put some pipe insulation on them — the regular R3 stuff in the box stores (the common split foam sleeve type) will work just fine for this purpose.


  5. Lis77 | | #5

    Thanks a lot, Bill. I've been stuck at this stage wondering how to proceed. I have insulated the pipes with foam tubes but then there is the shower valve which isn't so easily insulated.

    In your opinion, would I be better to seal this panel with some foam weatherstripping around the edge so it is sealed tight, to prevent air from migrating into that space? Or would that be sealing moisture into the stud bay?

  6. Expert Member
    BILL WICHERS | | #6

    I would probably just make the access panel fit tightly against the wall and not worry too much about sealing it. I’d seal the plumbing penetrations in the top plate and where they go down into the floor though. My thinking has always been to seal the tops and bottoms of interior walls just for some extra insurance against sneaky air leakage paths and bypasses. It’s quick and cheap to do with a can of great stuff.


  7. Lis77 | | #7

    Thanks a lot Bill, I sure appreciate your help!

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