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Home Repair Basements

Basement wall insulation

last year

Hello,

In an attempt to insulate the basement more, stop some mild condensation, create a vapor and thermal barrier and make it warmer, I am thinking of doing closed cell spray foam of 2 inches (5 cm) in the crawling space ( headers) at the top and the first top 2 feet of the concrete wall. After that I will cover the whole wall top to bottom with a typical pink insulation R12 and vapor barrier, all the way down to the slab. Is this a good idea? Will this stop most of the cold and all condensation?

I live in a cold Canadian climate where winters can reach -15C and colder.

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Comments (5)

Julie Praus
last year
Use closed cell spray foam on the entire wall as thick as you can afford with a 2” minimum.
worthy
last year
last modified: last year
Sounds like you're in the Canadian sunbelt, Climate Zone 5. Two inches would give you R-12, just 25% below the recommended minimum R Value for high performance homes from Building Science Corp.

Forget moisture-sensitive insulation such as fibreglass below grade. A vapour barrier is pointless and not required with ccspf.

Be aware that offgassing from ccspf will make your house uninhabitable for at least 24 hours after installation. For that reason, I've used it in new builds only. CCSPF must be covered by a thermal or ignition barrier.
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worthy -- thanks for replying... unfortunately, I can not slide in the XPS behind the studs. By local code, we had to install fire blocking on the end of the wall. So now it is closed off. And, I can't install XPS in between the studs becuase I already have electrical and piping running through the studs. The gap between the wall and the stud is only a little more than 1/2". So even if I could slide in the XPS behind the studs, I would only get about r 3 value.... Thats why I figured it is almost better to put no insulation. The pipes arent gonna freeze; Plus, if I do get moisture back there, then there will be no fiberglass insulation to get wet. With no insulation, the wall will just dry out. (with the help of my dehumidifers and the bathroom vent fan, of course) If I get a chance, I will post a picture tonight of the studded wall with the roughed-in plumbing and electrical. thanks again. mm I'll try to post a picture later....
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I was going to give you the stock answer--dampproof the interior foundation wall, replace the batts and vapour barrier as per Codes. But the fact is that Building Codes are woefully behind building science research into the best ways to ensure healthy, energy efficient basement living space. (See the link below.) I'd rip out the framing you have--chances are the builder didn't even place dampproofing beneath the plate. Then fix board-type insulation against the walls, eg., Styrofoam SM, with either the appropriate adhesive or concrete fasteners and fender washers, seal the joints with air-barrier tape (red and very sticky) caulk the joints at the top and insulate and caulk between the joists at the rim (NO BATTS). Next, build a stud wall, preferably of light gauge steel, add batts if you want to superinsulate or just drywall without a vapour barrier. (This is the way I did our custom home last year--though unfortunately, the inspector insisted on the vapour barrier.) And it's the way I intend to finish a custom home I am doing for a client starting next January. Here is a link that might be useful: Basement Insulation Systems
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R 23.8 is the minimum basement wall insulation value for the Energy Star 2012 Standard in either of Saskatchewan's very cold climate zones. The cheapest retrofit interior way to reach that minimum while avoiding condensation in the basement wall would be two-inches of XPS against the interior of the foundation wall, (R-12) followed by fibrous insulation between wood or light steel framing with no vapour barrier. Building scientists Joe Lstiburek and John Straube, among others, recommend this system. (Variations that either eat up more interior living space or cost more in most cases, use ccspf, expanded polystyrene boards (EPS) or polyisocyanurate boards.) The key detail area is the space around the rim, which, ideally, should be sprayed with closed cell spray polyurethane or fitted tightly with foam board, sealed and caulked. This post was edited by worthy on Wed, Aug 21, 13 at 14:14
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HU-208727471
Original Author
last year
Great information. Your're right and you know your stuff. I'm in eastern Ontario. thank you. The headers will be at 3.7in with a rocksol cover, so at or above code. The reasoning for the concrete walls is that most if not all condensation happens on the top 2ft of wall where it's coldest and a dewpoint is reached. The 2in of spray foam (Gynex) of that top 2ft of wall will provide the air barrier I seek, and should stop all condensation. Which would spray overlap with the black tacky tarp remaining on the wall below it. Then with a pink bat fiberglass at R14 covering over the entire wall from top to bottom, it will provide that addition R value at the top and also the bottom. So a great thermal barrier. Then an additional poly cover from top to bottom again to provide an additional vapor barrier. I have a extra fresh pink insulation to use so there's no extra cost. I just have to by a small roll of poly and tuck tape and some labor on my part to re-install.

Yes to 24 hours out of the house for full cure.

I'm doing this partial "flash and batt" because I think its the most cost effective way.

Is this reasoning good? Are their still risks to developing condensation behind walls? Should l get spray foam down to 3 feet?
Julie Praus
last year
I’m not sure what product the “black tacky tarp” is, but if it qualifies as a vapor barrier and you use a closed cell spray foam, which is a vapor retarder, then put poly over the whole thing, you would have a double vapor barrier. This would trap any moisture in the batt insulation. I would use a smart barrier product for the interior poly so moisture can move either way in your wall.
worthy
last year
last modified: last year
Poly over fg directly on the foundation wall is a surefire recipe for mold growth.

Either continue with the ccspf. You can then cover that with fg. Or attach XPS boards down to the floor, followed by fg (better yet, rockwool). All of it must then be covered with an ignition barrier.

*******

Last basement I finished on a new build was 2" ccspf top to bottom followed by drywall on framing.

For others, I put 2" XPS on the wall followed by fg and drywall. The inspector required poly; Building Science Corp.'s Dr. Lstiburek says it's not necessary--but it doesn't compromise efficiency.

CCSPF was the fastest and tightest system. Pricey though.

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