Should I use spray foam to insulate a basement?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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)

Answer 4

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.