basement: interior procedures if exterior mineral-wool insulation? And foamglas experience?
For our upcoming build, I am considering exterior mineral wool basement insulation (Iowa Zone 5). I’ve read as many articles here as I was able to find on insulation in general and basement insulation in particular, and think I understand the pros/cons of exterior vs interior. The reason for thinking exterior is to have bare concrete on the interior to keep an eye on cracks and moisture and mold. Also, we would like to avoid interior rigid mineral foam because of chemical sensitivity issues — concerns about rigid foam are raised, for example, in this NRDC report: https:// s3.amazonaws.eom/hbnweb.dev/uploads/files/Qj5q/NRDC- 3o84%2oGuide%20to%2oHealthier%2oRetrof it_Final.pdf
If using mineral wool as exterior basement insulation:
1. Does moist air in the interior of the basement still have to be kept away from reaching the interior of the concrete walls? If so, wouldn’t this necessitate interior impermeable insulation despite the exterior insulation?
2. Would wood studs attached to the interior of the concrete (eg for wiring) still be at risk from contact with possibly damp concrete? If so, then again wouldn’t that necessitate interior impermeable insulation despite the exterior insulation?
Lastly, does anyone have experience with/information about foamglas interior insulation for a basement? Last I read it was discontinued for residential, but it has been recommended as an inert alternative to interior rigid foam.
Thanks in advance for any information/advice!
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Replies
otinkyad,
1. No, as long as you use enough exterior insulation to keep the concrete warm enough to avoid condensation.
2. Whether the concrete is insulated or not, any wood in contact with it needs to be either PT or separated by a sill seal. Another solution is to simply leave an air-gap.
Malcolm,
Immense thanks, once again!
One question regarding wood being in contact with concrete: I had read about sill seals and air gaps only for wood in relation to the concrete slab. But what you explained suggests that there could be an air gap or sill seal between vertical wood framing and the concrete basement wall. If that is what you meant, I'm not understanding how vertical wood framing could be stable with an air gap between it and the concrete wall -- would you be willing to say a bit more about this please?
Many thanks for your n^th helpful response!
otinkyad,
Most basements get framed with 2"x4" walls just like the ones you use for interior partitions elsewhere in the house. They are similarly connected to the slab below and floor framing above, without relying on the concrete walls for support or stability.
Ah, thank you for clarifying that! I have read about and seen builders defaulting to putting studs against basement concrete walls, and didn't make the connection that those studs could be away from the wall, just like for other walls.
Thanks a ton as usual, Malcolm -- it's truly appreciated.
otinkyad,
Good luck with your build!