Basement Insulation – Radiant Barriers
I am doing some basement insulation this fall. I am in South Western Ontario (Canada), near Georgian Bay (just so you know the kind of temperatures I am looking at). The house was built in 1910 (approx) and is brick on stud walls. Foundation is limestone rubble (with old mortar) and interior of basement wall is parged. No big water problem although the basement air gets fairly damp in the smmer if there is a lot of rain.
My intention is to insulate the space at the foundation/rim joist/floor boundary with batts of insulation and vapour barrier on the inside.
I will insulate from the rim joist to grade (approximately anyway) which ranges between 2′ and 4′ depending on which side of the house you are on. I read some stuff at www.buildingscience.com about insulating the interior of a basement with a concrete foundation. They suggest rigid foam insulation on the wall down to grade or slightly below with no vapour barrier since they would like to see the wall be able to dry out from the inside. I will, of course, take care of the necessary flame/fire safety measures re. the rigid foam insulation.
I have been looking at radiant barrier insulation systems. I am wondering whether I could improve things (and the bottom line, since the material is so cheap) by incorporating a radiant barrier with the rigid foam. From the manufacturer’s picture I believe I am supposed to apply the rigid foam directly on the wall, stud over it and then apply the bubble/foil radiant barrier. I would not go ahead, in any case, until I hear back from the manufacturer (www.reflectixinc.com). Anyone have any experience with radiant barrier insulation systems?
P.S.
I am not going to ground level because I am told that if I let the foundation freeze the “old, water containing” mortar in the wall will crumble and I will end up in a house with no foundation. This makes good sense to me.
Replies
DgH,
The Building Science site you've referenced has great info on this topic. Reading that site and your comments, I don't quite understand why you'd install a vapor barrier. The suggest rigid foam specifically because it DOES allow vapor transmission (drying of the wall to the inside) without allowing the currents of moist air to reach the cool wall surface. Concerning the radiant barrier--I thought about this, too, but all of these are also vapor barriers (vinyl/mylar/aluminum films), so they would impede the vapor movement you are trying to promote (to allow drying). I think it might be okay to apply it to some of the surfaces and this would still allow dfor vapor transport. For example-- say you have cement wall (source of water from outside), then 2" of EPS (approx perm rating of 1.5), then a stud wall with unfaced/extensively perforated fiberglass insulation (free flow of moisture and air) then drywall (perm rating of 50). (Higher perm rating = more open to water vapor movement). In this case, it might be possible to apply the radiant barrier (perm rating effectively zero) to the back side of the drywall when you put it up, but cover only about 75% of the surface (and leave an air gap between the radiant barrier and the fiberglass so the RB will actually function). Vapor flowing through the rigid foam to the inside would still find it's way out, since the gypsum board is very permeable and you've left a route through the radiant barrier.
I think the moisture/water problems in basements are so significant that I'll probably use thicker rigid foam, metal suds (or just furring strips attached to the concrete) and no fiberglass. I might use a radiant barrier with holes to allow the water through.
MarkW
Thank-you for your reply.
I was starting to think about the same. That is, that a radiant barrier might not be such a good idea. The only thing is that my knowledge of this sort of thing is mainly theoretical. I always like to check out my ideas with someone who has actually done it.
Thank-you.Last year I didn't know what any of this stuff meant.