continuous insulation for concrete basement walls?
blamus20
| Posted in General Questions on
Most people simply frame a 2×4 wall 24″OC in front of the concrete walls, spaced 1/2″ apart to avoid the wood contacting the concrete, and take care of any unevenness of the concrete. And then fiberglass between the studs as usual.
But are there clever ways to insulate a concrete wall using less lumber and therefore less thermal bridging? Any clever ways to do continuous insulation without added cost? Even if I used rigid foam boards applied directly on the concrete there’s still the issue of attaching drywall or plywood as the finish layer, and getting the finished surface flat and plumb (assuming the concrete isn’t perfect)
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Replies
Just off the top of my head it seems to me your limitation is actually the drywall. It will need support at no more than 24" oc no matter what.
I was in France recently and they have an interesting off-the-shelf product which is a 4'x8' panel of EPS foam, about 3" to 4" thick, with drywall bonded to one face. The houses are typically built with CMU walls and the panels are simply glued to the interior face. It's a very efficient workflow.
The one complication is that if you're running plumbing at an outside wall it gets attached to the CMU wall first, and then the EPS panels get routed to fit around the pipes.
I have no idea if a similar material is available in the States but it would eliminate wood framing entirely.
Consider Insofast: https://www.insofast.com
It's EPS foam with embedded plastic studs that the drywall is screwed to. I'm sitting in a room with it right now. It's a great product for this use case.
I would never use batts in a basement, there is just too much risk. Rigid foam all the way! :-)
If you use lower density EPS, you can press the foam against the wall and small imperfects (less than perfect motor, maybe a block or two that is a bit proud of the face of the wall) will squish into the foam so that the foam "evens out" the wall surface. This is harder to do with XPS, since XPS is less "squishy", and the same for polyiso. You can frame out the interior of the wall with 2x3s on the flat, which will then let you runn wiring easily using 4" square boxes that are 1.5" deep (which is the standard), and mud rings to bring devices up flush with the finished surface of the drywall. This is the most compact way to go, and probably also uses the lease lumber.
If your wall is pretty even, polyiso will get you more R per inch. If you don't need a wall that you can run wires and pluming in, you can either use something like Dow Thermax that can be left exposed on the interior, or you can put 1/2" drywall directly against the rigid foam and secure it to the block wall using long tapcons. There is no requirement to frame out a full studwall in these situations.
Bill
blamus20,
You may find this article useful: https://www.greenbuildingadvisor.com/article/three-ways-to-insulate-a-basement-wall