Exterior Wall Batt Insulation Newbie Questions

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Old 04-08-18, 01:27 AM
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Exterior Wall Batt Insulation Newbie Questions

hello!

so short story, there was a leak from the shower above, so all the drywall and insulation was removed by a mitigation company. now i have to put it back.

the wall is an exterior wall. 2x4 construction with 16 inch on center. i purchased R15, kraft paper faced, 15 in wide, 3.5 in deep by 93 in long.(i believe i only have to get R13 but the R15 package was the ideal amount and cheaper. i live in seattle, wa). so i'm planning on stapling the paper flanges on the inside surface of the studs. my questions are regarding, electrical wires, copper pipes and ABS drain pipes.

1) are you supposed to stick some insulation behind the electrical wires and then fully cover with the batt insulation?
2) are you supposed to stick half insulation behind the ABS drain pipes and the rest on top so that you can't see any ABS pipes?
3) or can i just install the entire insulation behind the ABS piping (i would end up with the kraft paper behind the ABS pipes?
4) same questions with copper piping?

i've attached some pictures to help.

as always, thanks for any input!
 
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Old 04-08-18, 08:41 AM
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#1, R-15 is for 2 X 6 walls not 2 X 4, compressed insulation lose's R value.
#2, Modern codes would call for 2 X 6 walls in your area, since you now have a blank slate to work with if it was mine I'd be building that wall out with 2 X 2's and using that R15.
The outlet would need to be moved out so it would set 1/2 out from the new wood.
If there's enough room you can slip 1/2 blue foam behind the plumbing, the wiring is not an issue, insulation goes right over it.
There is no way to slip batts behind that plumbing.
Once the insulations up I'd be adding a vapor barrier.
 
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Old 04-08-18, 10:19 AM
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thanks for the reply!

i was under the impression that the batt insulation i purchased is made for 2x4 walls? and that the whole reason to get faced insulation is that it would act as a vapor barrier?

also, you're right.. there is no space behind the large diameter vertical ABS drain pipe. there is about 1/2" to 3/4" inch behind the smaller diameter ABS plumbing? so do i just cut the insulation around the smaller diameter drain pipe (ie put some to the left and some to the right of the pipe)?

thanks!
 
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Old 04-08-18, 11:44 AM
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R15 is for 2x4 walls. You can slit the insulation to go halfway over things like water pipes or horizontal romex. You should cut out the fiberglass where you have large pipes... just slit the fiberglass not the kraft paper, and pull out the fiberglass so it fits over the pipe. If there is room behind, you can stuff some behind, but if there is no room don't worry about it.

Kraft insulation is a vapor retarder, not a vapor bartier, and it is all you need. Blue foam behind obstructions will be far superior to cramming fiberglass behind.
 
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Old 04-08-18, 01:14 PM
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thanks xsleeper!! that helps a lot.
 
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