Insulating Walkout Basement Walls
Hello All,
I would appreciate any help on pointing me in the right direction. I am in the process of finishing my basement which will convert it from an unfinished space to a finished space. It is a walk out basement with about 50% of the walls concrete below grade and the other 50% is standard framed construction with 2”x6”, Osb sheathing, and velvet house wrap under vinyl siding. These walls are above grade. The buildee left faced r-19 fiberglass insulation in these cavities.
For the concrete, I am leaning towards 2” XPS behind 2” x 4” framing with unfaced fiberglass or mineral wool in the walls. This would be for the walls that would be finished space. For the mechanical areas I was going to do 3” foil faced Thermax to save on some space.
I am really struggling on what to do with the framed walls above grade. I was lead towards foam board and batt by putting in 2” XPS board in the cavities, and the 4” of unfaced fiberglass or mineral wool insulation in the wall to complete the installation. The XPS board would be sealed with spray foam. My other option is to just replace it with faced fiberglass unless anyone has some other ideas.
Another option I am considering is just using The aluminum faced thermax everywhere but I am not sure if that would create double vapor barriers / moisture problems anywhere.
Any help is appreciated. Basically, I am looking to see if the foam board and batt strategy is even worth it if I can use thermax in lieu of cos behind / in the walls.
Thanks again.
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Replies
The above grade walls can be insulated in the usual way, there is no need to do anything special with them just because they aren't quite as tall on their own.
For the block, I would insulate with polyiso exclusively and not bother with interior side batts. You could then furr out the upper part of the wall to give you an even surface on the interior. This doesn't need to be a full 2x4 wall, either, you could just use 2x2s or 2x3s on the flat over the rigid foam, that will still give you enough space for electricals (use 4" square boxes 1.5" deep and mudrings to get up through the drywall, these are all standard parts). Framing out an entire wall on the interior just eats up space.
I would use polyiso everywhere and not XPS. You get more R per inch that way, and the derating issue for cold weather doesn't really come into play in the more sheltered areas you'd be working with here.
Bill
Hi Bill,
Thanks for the response and makes sense. I’ll have to look into this a little further but I think this will be the best way forward. Thanks for your input