Rim Joist Insulation and Basement Fix

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Rim Joist Insulation and Basement Fix

Post by Brent01 » Sat Dec 22, 2018 2:59 pm

Hello Shannon & fellow Home Improvers,
I bought a fixer upper in Ottawa and am looking for a 2nd opinion/guidance on how to fix up a couple basement issues. I'm using "A Good Way To Insulate Your Basement Walls" and "How To Install Fiberglass Batt Insulation & Vapor Barrier" as my main guides. Essentially, one of my exterior walls has moisture/water issues, I haven't detected anything with the other walls. I'm fixing the root cause (bad grading and 2 foundation cracks) and am looking at what to do inside the house once these fixes are done.

Here's my plan:

Step 1 - Insulate my rim joist between the studs using 2" xps and expanding foam, use Roxul on the interior side of that for fire safety. Note, the top of my poured concrete foundation would still be exposed at this point, but I'm thinking I can get through this winter with this fix.

Step 2 - Remove existing interior wall with moldy drywall, no vapour barrier of any kind, and rotting bottom plate. Install xps against concrete and bridge the gap from wall xps to sill plate xps with more xps and expanding foam.

Step 3 - Install a new wall with poly vapour barrier. Re-install roxul between the joists as a fire break.

My questions are:
1. Do I need to/what is the best way to vapour barrier between the joists above my new wall? More xps and expanding foam? poly/acoustical sealant? nothing because it's not required?
2. Did I miss anything/get something wrong?
3. The wall parallel to the floor joists doesn't seem to have a vapour barrier that connects to the sill plate or floor joist. Can I simply fill the gap between the interior wall top plate and floor joist with expanding foam or is the proper fix to remove this wall as well and repeat the above?
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Re: Rim Joist Insulation and Basement Fix

Post by Shannon » Sat Dec 22, 2018 3:26 pm

Most places will allow well sealed 2" rigid foam to qualify as a air/vapour barrier. So you can place a piece horizontally across the top of the basement concrete wall and onto the top of the top plate of framed interior wall and one above that vertically against the sill plate. All of this would be sealed with canned spray foam.
Other then that you got it.
For the parallel wall you could remove it and be sure the insulation is done as well as possible. In many cases the access is pretty tight in these areas and a perfect job is almost impossible.I insulate them as well as possible and run my poly up to the joist above and seal it there.
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