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Insulating Unfinished Basement

Help!!! I want to insulate the unfinished portion of my basement. I live in St. Louis, MO. My basement walls are poured concrete. I have about 4 feet above grade and four feet below grade. No water leakage.

I have read the Building Science article. The foil faced foam rated for exposed use sounds great but is very hard to find and the one quote I got was about $100/ 4x8 sheet. I assume the article is referring to "Thermax" by Dow.

I'm really not interested in putting the regular foam up because then I have to drywall.

The perforated fiberglass blankets seem reasonable but I still worry about mold. But this seems to be my only option. I would insulate the top four feet, the above grade portion.

Am I stuck or is there a way out of this? My floors are freezing! I want to do the walls instead of the basement ceiling so I can take advantage of the rising heat. Also, my furnace is in the unfinished portion, and I could hold some of that waste heat in.


Re: Insulating Unfinished Basement

It sounds like using the fiber glass bats may be what you need. You really don't need to use the plastic wrapped bats since they aren't a vapor seal they are just wrapped for ease of handing against irritation ... there is no increase in performance and in my opinion not worth the up charge over regular bats.

Just make sure to apply a continuous sheet of vapor barrier over the bats and to ensure that it's completely sealed. This will ensure there will be no moisture soaking the insulation to encourage mold.

One of the main areas to concentrate the insulation is the rim joists this will help greatly reducing the cold floors.

You hadn't mentioned if you would be framing the 4 foot section that would house the insulation otherwise how do you intend to keep the insulation in place?

If you are putting wood framing in place make sure you isolate the lumber from the concrete with either tar paper ( felt paper) or sill seal or even house wrap.

Hopefully this helps.:)

Re: Insulating Unfinished Basement

Thanks Canuk.

My thought was that I would install the perforated vinyl blankets to the top 4 feet via horizontal furring strips. The blankets hang from the furring strip attached to the sill plate. Simple and inexpensive. The concern is trapping moisture in the blanket. Supposedly the perforation allows moisture to travel back and forth.

I disagree with installing a vapor barrier. That would only trap moisture in my opinion.


Re: Insulating Unfinished Basement

John ... since you are only insulating the top portion of the wall and the coldest part leaving the insulation uncovered will encourage moisture. The vapor barrier is the barrier that separates the warmer moist air inside the basement from coming in contact with the colder air at the foundation ... especially the level above grade.

Leaving the insulation uncovered and letting the moisture travel back an forth will reduce the performance of the fiberglass bats. Depending on how cold the foundation wall above grade gets you might find frost build up between the insulation and the concrete. Time will tell.

Good luck.:)

Re: Insulating Unfinished Basement

In general insulation shouldn't be left exposed. Craft face fiberglass stapled to studs needs to be covered. The paper is flammable & needs something like drywall over it. A foil faced scrim insulation can be left exposed, but it should be stapled to studs. I doubt if the plastic encased insul is rated for exposure. I would also be concerned about the fiberglass getting in the air if the batts & exposed ends are hanging. It may not be asbestos, but I don't want me or my kids to breath it.

As far as I know all foam insulation even foil faced rmax needs to be covered inside a house. I think the best way to insulate the wall would be to stud or furr out the wall & put batts or foam between or foam over & then cover. Leaving a small gap between wall & stud is good. If you don't take the insul all the way down, take it at least 2' or 3' beyond grade.

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