insulation for concrete basement wall and ceiling

Old 06-22-16, 05:58 PM
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insulation for concrete basement wall and ceiling

I'm redoing a small reception room that is 50% below grade (it's on a slope outside).
The current insulation was 1 inch Styrofoam but I'm not sure this was enough as the room was always a bit damp and cold.
We were thinking of adding 2 inch Styrofoam but the room is only 50 sq ft of floor space so every inch counts for a bit of extra room.
The walls will have framing/strapping and then paneling on top.
Is there any high density durofoam or something similar that could be put it in to be only 1 to 1.5 inches thick with good insulation?
Don't want it to be too expensive so can't use foam injection or other methods.
Old 06-22-16, 07:03 PM
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XPS is typically R5 per inch. Poly-ISO can be higher, 7 to 8, but performs worse in cold weather and the R value degrades over time as it outgases.

I think Owens makes a high R XPS, but IIRC, it's only slightly higher, like 5.7 per inch. Plus, it's very hard to find.

I think XPS is your best bet. You may want to look at one of the systems that has built in strapping or channels for strapping as that will help maximize the insulation thickness per overall wall thickness. Searching for basement finishing systems will find you a few varieties.

You may want to look at improving ventilation to help with the damp/cold feeling after you've improved the insulation as much as you can.
Old 06-23-16, 04:25 AM
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The resulting temperature in that basement is the combination of heat loss, air infiltration, and heat supplied. Supply enough heat and the basement will be very comfortable, but your heating costs will rise. So insulation is not as much a question of comfort but how much that comfort will cost.

The air infiltration I mentioned is probably the larger contributor your comfort issues. Unless a specific effort has been made to seal the house to foundation and the entire rim above the concrete, there is most likely a lot of cold air leaking in. I do energy audits with an infrared camera in a cold location and that area ALWAYS shows leakage.

As for the 1" of rigid, you said there will be framing to the inside. Will this be standard 2x4 framing? If so, then those cavities can be filled with additional insulation.

Not sure where you are in CA, but there are probably code minimums that will not only make your work acceptable, but meet your comfort needs.

Old 06-23-16, 04:01 PM
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Not sure what the code is for a concrete wall TBH.
Presume that 2x4s don't even have to be used so could be much thinner as there's nothing to support, it just has to hold up.
Having said that, if studs are used, then there should be 2" of space for styrofoam.

There is a lot of cold draft coming in, you can feel it in the winter despite the outside walls of the basement area having Styrofoam.
The 2nd floor is much much more comfortable and has the same insulation so it's either foundation or dampness issues in the finished basement area. It's a slope so back of the room is below grade, front is open and the sides are 50% as they are with the slope.

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