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Issue Insulating an exterior bathroom wall

jwolf1028 | Posted in General Questions on

Currently doing a renovation in climate zone 5 in a house that I am taking over. Built in the early 2000s.   Took down the sheet rock in a bathroom and was greeted by what I am seeing in the attached photo. Looks like a really poorly done batt insulation job, with insulation improperly stuffed in between pipes.   

I was all set to do two layers of rigid foam with spray foam around the edges, as it says in the green building advisor detail library, but the issue I’m seeing is that there are tons of little stud bays and pipes.  This seems to make it a lot harder to do a cut and cobble approach with rigid  foam than I was expecting. I was expecting a few much larger stud base to work with. 

I am trying to avoid spray foaming the whole wall, because I worry about possible off-gassing and fumes from spray foam jobs done bad.  

Any advice anyone can offer here? Thanks so much! 

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Replies

  1. Expert Member
    Akos | | #1

    No easy answer here. Stuff the bays with as much fluffy as you can get in there and then get a solid air barrier (around me that is 6mil poly) over it. This should be sealed around the perimeter and windows with acoustic caulk. If the barrier is done properly, you should not feel any draft through that wall.

    I would also nail plate all the plumbing, easy for a drywall screw to go through a drain line and end up with a slow leak/smell over time.

  2. jwolf1028 | | #2

    Good call on the nail plates! This is why I come here again and again.

    Thanks for the feedback! I might actually do rockwool with a smart membrane over that. Any cons compared with Kraft batts that you or anyone can think of? Thanks!

  3. Expert Member
    BILL WICHERS | | #3

    Rockwool is likely to be easier to install well in a complex wall like this since it will stay in place better without being overly "stuffed in". I actually prefer a seperate vapor retarder over kraft faced batts because it lets you put all the batts in nicely, then do the vapor retarder as a seperate step over the entire wall, all at once.

    BTW, you need nail plates over electricals too, not just over plumbing.

    Bill

  4. begreener | | #4

    I wouldn't use spray foam, but rather injectable, slow curing, 2-part foam ...

    Take a piece of 1/2 plywood (2 feet in width & cut to a length that makes sense) & cover one surface with a sturdy poly sheet

    Screw this to the wall at the bottom with the poly side facing into the wall - this is now like a "concrete form", but rather for injectable foam (which doesn't stick to poly so it can be removed easily).

    Inject foam behind the plywood in 18" "lifts" & let it cure...

    Remove the plywood "form" & inspect the foam for coverage around pipes & quality

    Go up the walls until completed

    https://energyefficientsolutions.com/products/handi-flow-cavity-fill-slow-rise-insulation-spray-foam

    ~ Former spray & injection foamer in VT

  5. Expert Member
    Akos | | #5

    I'm not a fan of spray foam (or pour foam), but also not against it in most case. In this case, embedding all the piping in foam means a heck of a demo job if you need access. I would stick to easy to use fluffy.

    The facer on batts works great as the code require vapor retarder, but it is impossible to air seal. A sheet vapor retarder can do dual duty and provide both air sealing and vapor control. It doesn't matter which one you use, in zone 5 regular 6mil poly will work just as well as one of the fancier variable perm membranes. Seal this to the Tyvek flaps around your windows and if not done already, foam the windows in with low expansion foam.

    One thing to watch is you don't want insulation between the water supply lines and drywall. You want to keep these as close to room temperature as possible. It might be even worth it to cut and cobble a nice foam cubby around them to minimize air leakage.

    1. begreener | | #6

      A "heck of" a demo job vs a "heck of" an air sealing/cubby job ...

      jwolf1028 - pick your poison!

      1. Expert Member
        BILL WICHERS | | #7

        Air sealing with everything accessible is going to be a whole lot easier than chipping pipes out of cured foam down the road when everything is covered up if you ever have to fix anything...

        Bill

  6. Chris_in_NC | | #8

    Looks like a completely normal fiberglass bat installation. That is to say, pretty bad.

    Get some mineral wool and a serrated insulation knife, and start cutting to fit.
    The Rockwool brand is probably my favorite for the work I've done like this; the other (maybe 2) brands I've used seem to be less dense (or maybe the fiber orientation is different), which makes them more difficult to cut to fit around pipes, irregular cavities, etc. You can be as surgical as you want with Rockwool. I wonder if the TimberHP TimberBatt would also be really good for this type of batt sculpting....
    Zero issues with the other mineral wool brands for normal walls, but I'd opt for Rockwool for those weird areas in your bathroom.

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