10:27PM | 01/09/14
This is going to be difficult to describe. We have an upstairs bathroom, the wall with the vanity and sinks faces what would be an outside wall but it is underneath the garage roof. The BR also sits partially above the garage.

We had a frozen pipe (has happened a few times) and one finally busted. Once the plumber cut the hole to fix the leak I could finally see what was in there. There is no real insulation in the cavity. There is the exterior wall then a gap then the interior wall which is insulated.

I want to insulate the area better where the pipes run through but I am not sure the best way to do it. My thoughts so far are:

(After patching the hole of course)

1) Spray foam the cavity - Cons cost and I don't know if this would be a problem since the interior wall is insulated. Would also have to put some kind of block between the floor batting insulation and the foam where they would meet.

2)Spray foam the outside of the exterior wall - Cheaper but would this be enough and again would it be OK since the interior is insulated. I think it would since there would still be an air gap between the walls.

3)Blow in cellulose insulation. Cheapest option, but would it be enough plus there is always settling that occurs, maybe combine this with spray foam on the exterior.

4)Some other solution I am missing.

I am attaching one picture I have of the repair which kind of shows what it looks like inside. The exterior wall is just plywood with tyvek on it.
20140109 121452

Duane, Moderator

11:10PM | 01/09/14
Member Since: 11/14/13
91 lifetime posts
It appears you could have 2 problems, one of course as you noted you have plumbing pipes in a unconditioned space and that needs to be corrected. You typically need to install insulation against a ridged air barrier ( outside wall) The issue becomes a dead air space between the outside wall and the existing interior insulation. I can not tell you for sure ( the picture helps but I can not make a determination by it) 1 possibility is to spray foam the entire area to insulate and to take away any air barrier between outside wall and interior wall. This should stop the freezing and the air infiltration that is possible in that area. I would however suggest you have a insulation expert visit the job site and make a determination. You will want to be careful as you do not cause conditions for mold.

Duane, expert moderator
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