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Old 09-25-2015, 06:01 PM   #1
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Basement insulation questions - 1930s home

Hi all,

We had a small finished basement area (approx 250 sqft) in our 1930s home. It was done in probably the 1970s, then updated in the 1990s. We wanted to redo it and tore it completely out, and encountered (as suspected) quite a rodent problem as well as some mold.

The space is partly below grade and consists of the back exterior wall of the house (4ft high slanting concrete foundation wall, topped by 5 feet of stud wall with clapboard siding. The side walls are stud walls on 8-12" of foundation (house is attached on both sides) with clapboard, and I assume a small air gap of a few inches between the houses? The clapboard has some kind of kraft-type vapor barrier on its inside face, intact in most places though damaged by rodents in several places as well. Many gaps between siding and mudsill.

The POs had drywalled and insulated with fiberglass (no insulation on the concrete wall). For the most part, the moisture issues were fairly limited (we are in climate zone 3 and near the coast, so rarely see temps below 40 and above 80). There was some lumber mold growing on some studs near uninsulated plumbing or ductwork, and in some places clearly affected by air leaks from the porous exterior wall. We determined most of the odor and destruction of the fiberglass to be due to the rodent infestation, not mold or major moisture issues.

That being said, we will now be re-insulating after cleaning up and patching the large air leaks. I'd like some guidance on my insulation options. Priorities are
1) moisture/odor control
2) sound control - attached neighbors so controlling sound is important to us
3) thermal - despite the air leaks, the space was actually quite comfortable even with the R11 fiberglass

My initial plan was to use 2" EPS (R-7.7) in the stud bays and on the concrete (taped seams and foamed gaps), with either Roxul or fiberglass after that for additional sound control and R value. This will all be topped with drywall on furred out 2x4 walls.
1) In terms of attaching the EPS in the stud bays, is it best to adhere it to the clapboard or just snug it up to the clapboard and adhere with foam to the studs?
2) Should I remove the building paper?
3) Any other strategies that would be better?
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Old 09-26-2015, 06:10 AM   #2
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How is the sill in that firs picture?

Shouldn't be any moisture considerations between the two attached walls. In those cases, you want to strive for sound performance (assuming they are airtight attached walls). Seal up all the gaps and cracks and then insulate. If you aren't going to be building a staggered wall, the framing is probably the primary source of noise transmittance there. If it were my home, you could use that same EPS between the studs, sealed up well, some rock wool, and then an interior wall with an air gap. Depending on how soundproof you want it, some sound controlling drywall, resilient channel, air gap, etc. There are a bunch of different strategies depending on how good you want it to perform.

What type of siding is on the exterior of the home? Is it vented like a vinyl siding?
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Old 09-27-2015, 10:48 PM   #3
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So you have clapboard siding with a kraft paper stapled under it, directly on the studs. But you are showing two different walls- if that is a window in last picture?

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