Finishing a basement room below grade in Climate Zone 5
Hello, I have a questions regarding finishing below grade walls in zone 5. We have been researching the correct steps to finishing these walls but seem to get different answers depending on whom we ask. I went to our county and state code websites but didn’t get clear answers there either. I would love to get some feedback to hopefully simplify the answers for us. Thanks for your time!
Christy W. Madison WI
1. Is it best to leave a gap between the framing and the concrete below grade wall?
2. What kind of insulation is best, Styrofoam, spray foam, etc for below grade walls?
3. below grade does not get a vapor barrier correct?
4. I’ve seen basement framing done with furring strips, over time won’t this be a problem with mold and moisture?
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Replies
Christen,
As a first step, I urge you to read this article: How to Insulate a Basement Wall.
After you read the article, if you have any follow-up questions, feel free to post your questions here.
If you're installing a studwall to hang the finish wall, in zone 5 you can go ahead with 1" of foil-faced polyiso (seames taped) trapped to the foundation with the studwall, and install unfaced or kraft-faced batts. That would meet current IRC code performance, and would be sufficient foam-R for dew point control at the foam/batt boundary that it would not need an interior vapor retarder to control wintertime moisture accumulations.
With polyiso it's wise to leave an inch between the bottom edge and the slab to prevent moisture from wicking from the slab into the polyiso. It's also wise to put an inch of expanded polystyrene insulation (EPS) under the bottom plate of the studwall (so take it all the way to the foundation wall too, under the bottom edge of the polyiso, and seal them together with can-foam ). The EPS keeps the studwall bottom plate warmer, which becomes important in summer, since an un-insulated slab in your area would be below the average outdoor air dew point, which can cause the wood in contact with the slab to take on moisture in the summer, risking rot/mold.
thank you for both responses! They're very helpful.