rigid foam recommendation for retrofit of interior basement wall
I’m finishing a basement room to make an office. Basic plan is to use rigid foam on the interior of the exterior block walls with 2×4 framing in front of the foam.
I’m looking to source the foam boards and see this product:
It has foil on both sides, is that advantageous for any reason in my application? Or is there a reason to avoid the foil?
It also claims:
Produced with an EPA-compliant hydrocarbon-based blowing agent that has zero Ozone Depletion Potential (ODP) and virtually no Global Warming Potential (GWP)
Can anyone recommend this product for my application, or perhaps suggest an alternative? I’d also be open to reclaimed foam board if someone has a source for NJ.
Thanks for any feedback!
Rob
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Replies
> It has foil on both sides, is that advantageous for any reason in my application? Or is there a reason to avoid the foil?
No problem with the foil.
> Can anyone recommend this product for my application, or perhaps suggest an alternative?
I recommend Insofast (https://www.insofast.com) for insulating basement walls you plan to drywall. The EPS panels install easily and have an integral plastic "stud" to attach drywall to. There are also channels to run wires. I have it in my own basement office and can't imagine using anything else.
Polyiso works fine here, as long as you don't have a basement prone to water problems. If you get the occasional small amount of wet floor, just keep the bottom edge of the polyiso an inch or so above the floor. You'd want a capillary break under your sill plate here too if you're framing walls on top of the floor slab. If you have a completely dry basement (no bulk water), there is zero downside to polyiso here. Foil facing or fiber facing, either works fine in this application.
If you have bulk water issues, then you want something that won't wick water, which typically means EPS or XPS. I'd use EPS in this case, since it's both cheaper and greener. You'll need a thicker layer of insulation with these materials compared with polyiso, and remember that in a basement, the "polyiso is worse in the cold" issue that you sometimes hear about doesn't apply -- basement walls will always be a bit warmer in the winter than above grade exterior walls.
Regardless of which insulating material you use, I'd recommend against framing out full studwalls. You can save space and material by using 2x3s "on the flat" against the foam, then using 1.5" deep 4" square electrical boxes and budrings to wire the walls. The 1.5" depth of the 2x3s gives you a nice cavity space for wiring, and even smaller pluming supply lines.
Bill