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Old 12-13-2010, 04:23 PM   #1
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To seal/cap a wall with plumbing in it, or not...


I'll try to keep this as short and sweet as I can. In our attic, which has been way too warm during winter months, I moved the insulation around to do some air sealing. During this process, I uncovered one particular 150 sq. ft. nightmare area where lots of air sealing needed to be done. Here's the deal...

It's a cathedral ceiling townhouse with a loft, two bedrooms and a full bath upstairs. The area of concern is above the upstairs bathroom. There's a soffit box above the shower that was only 'sealed' by the primer on the drywall. (There was a vastly under-performing bath exhaust fan in the bathroom, next to the soffit box, which has since been replaced by a great one that has helped out tremendously... but we have lots more to do.)

On each end of the soffit drop, lies the north and south wall of the bathroom. Above them, in the attic space, when I moved the black-dust-stained insulation out of the way I found that both of these walls are wide open into the attic - they have a top plate, but it is not equal to the height of the soffit drop. (see pic, here)...

This is the top of the south side bathroom wall, which is a shared wall with an adjoining bedroom closet. The north wall is not a shared wall, it is the wall of the stair case that leads up to the loft, etc. The north wall opening into the attic is roughly 40% larger than this one (i just didn't have the pic handy).

Both walls have plumbing in them. The south wall (the one you see, here) has the shower/tub connections. These pipes are polybutylene pipes, not copper, and so of course just have crimped connections if I recall correctly. In the north wall, there is a plumbing vent stack that connects to the toilet drain and heads all the way down to the basement.

I would like to either fill these walls with insulation, or cap them off with a combination of fiberglass insulation, rigid board insulation and 2x4s to prevent so much warm conditioned air from getting into my attic.

But... CAN I? Or Should I?

Are these walls supposed to be able to "breathe" in case of leaks? Are there some plumbing concerns I should be aware of, here?

Because I gotta say, just looking at these and feeling the amount warm air coming up and out of the wall cavities is really .

Any all help would be greatly appreciated!


Last edited by bkraz; 12-13-2010 at 04:29 PM.
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Old 12-14-2010, 09:32 AM   #2
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in case of leaks? Are there some plumbing concerns I should be aware of, here?
I'm sure there are people here that are more knowledgeable regarding your questions on the insulation.

My two cents however, would be to get rid of the PB pipe. Replace it with PEX. Especially if it's accessible now, and you plan to permanently seal the space later.


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attic , insulation , open wall cavities , plumbing in walls

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