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Home in CT cape w/ uninsulated basement. Its a cold, not drafty house, with new Marvin integrity windows. The basement is very cold, and it seems like the cold basement is making the rest of the house difficult to heat( forced air). So I'm considering insulating the basement walls which are cinder block.

I saw one plan with foam sprayed directly onto the block, then there were 1 1/2" metal studs installed on top of the insulation, and then sheetrocked w/ 1/2". Has anyone seen this done? It doesn't explain how to install the metal studs. Would it help even if I didn't insulate the below grade walls?

  • I live in central Ohio so I might not understand your plight, but I never understood insulating the basement walls. The basement walls are insulated by earth. How far down does earth get below 55 degrees? 2 feet? I think insulating the rim joist is the most important part, plus you don't trap moisture behind your walls. Do you have any furnace vents pushing warm air into the basement? – Evil Elf Jan 7 '16 at 13:39
  • With block walls I think you may end up with mold problems with insulation. I lived in Dayton Ohio in the early 80's and installed fir strips that I attached sheetrock to The basement did feel warmer since the cement walls were not radiating the cold. (I did not add any additional heat ducts). – Ed Beal Jan 7 '16 at 14:39
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    Earth is not a thermal insulator, at least not compared to actual insulating materials. – iLikeDirt Jan 7 '16 at 15:28
  • @EdBeal it's not the insulation that causes mold problems, it's how it's installed. If there are water problems, sheetrock by itself isn't ideal as it too can allow for mold growth. – DA01 Jan 7 '16 at 19:43
  • "Radiating cold". That's a new concept. :P – isherwood Jan 7 '16 at 19:44
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That's the expensive way to do it. The cheaper and just-as-effective method is to put rigid foam boards (EPS or XPS foam) up against the walls, and seal their edges with little bits of spray foam, caulk, and tape (as appropriate). Seal them to the floor too. You can use the same method to insulate the rim joists. Just make sure everything's sealed up tight so no inside air can reach the walls and rim joists. This is much cheaper and more DIY-friendly, and the results are just as good. These foam boards are easier to finish too since they're flat and straight, so you can lay drywall right over them, fastened to the block walls underneath with Tapcon screws. Or you can build a stud wall and drywall over that.

For bonus points, use cementboard instead of drywall for the first two feet off the ground for flood safety. Drywall will dissolve and grow mold when soaked; cementboard will just happily sit there. If you build a stud wall, use pressure-treated lumber for the same reason.

If you choose to finish the basement, use the same approach and avoid moisture-sensitive materials in the bottom few feet just in case the basement floods. This means tile or plastic baseboards, trim, and flooring. No carpet, no hardwood, no MDF, no paper, gypsum, or wood products in general.

  • Good answer. One note, though...it's hard to finish cement board. I'd suggest using a non-paper based sheetrock such as Densarmor instead. – DA01 Jan 7 '16 at 19:40
  • The gypsum core will still turn to mush in the presence of standing water, though commercial-grade gypsum sheathing products are indeed better than residential drywall and may last a bit longer and accumulate less mold when immersed. Were it my basement I'd use cementboard and cover it with a skim coat of lime plaster to match the surface of the drywall above it. Well really, were it my basement I'd use all cementboard and no wood or drywall at all. :) – iLikeDirt Jan 7 '16 at 20:15
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    @iLikeDirt...oh, true...good point about standing water. (though I think if I had standing water, I'd be paranoid and want to tear out everything below the water line anyways...) – DA01 Jan 7 '16 at 20:20
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    But if everything below the water line is inorganic and water-insoluble, you don't have to! That's the beauty of it! Total peace of mind! No worrying that there's hidden mold or structural damage because the submerged materials simply do not allow them. – iLikeDirt Jan 7 '16 at 22:07
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    I know that's true in theory...but given that we had mildew growing on concrete in our old basement, I'd still be paranoid that SOMETHING was growing inside the wall :) – DA01 Jan 7 '16 at 22:11
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Closed-cell spray foam would be an excellent insulator, and would prevent some mold problems that can result when other types of insulation are installed against concrete by eliminating air gaps. Ask your installer whether you should seal the block wall first.

Steel stud walls would be free-standing (fastened at the floor and ceiling), and would be installed just inside the foam layer.

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Should I use spray foam to insulate

Yes.

Well, usually. Given the budget, it's often the best way insulate a home in terms of r-value, vapor retardation, and speed of install.

If you go that route, no need to install the studs outside the foam. You can put up the studs (leaving a bit of a gap between the wall and stud for foam to get behind), and then have them foam in between. This gives you the added bonus of a really sturdy wall. That said, framing outside of the foam gives you a bit more flexibility in being able to run electrical and plumbing afterwards.

But it can be pricey, so I'd definitely take iLikeDirt's suggestion. In fact, that's what I've done myself: XPS foam boards, seams taped, metal studs, Densarmor wallboard (fiberglass faced sheetrock)

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As a former plumber & drain-layer I would be checking for signs of ground water as that is the main source of chill in a basement. Otherwise the basement would be a slightly cooler temperature than the house above, not chill cold as here. Look for overflowing gutters, broken downpipes or ground water coming downhill from a neighbours house with similar problems. Stop the ground water coming against your basement wall and/or the floor and your problem is solved. If the floor then the floor will be colder to your touch than the cinder block walls. If you have stray water and need to shift it then the best solution is to dig out the outer earth against your block wall 200mm (8") wide and install 110mm perforated drainflow pipe & surround with 50 to 100mm with 20mm GAP (General All Passing) drainage gravel and fill with gravel to just below the outside earth level leaving enough soil depth for your garden or lawn. Run this drain pipe out each side of the basement/house to a lower drain point to discharge the water away from your house. If successful your basement should be quite cosy with no further work required. To fix a cold floor, then install your drain at or below the base of the wall to discharge the water before it reaches your floor.

If your house and basement is on level ground then you should discharge your new drain into a sump chamber below & outside the basement walls and install an automatic discharge pump to lift the water into the council storm water drainage system.

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