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Community and Q&A

I may need to tear out some insulation

user-2423385 | Posted in Energy Efficiency and Durability on

Ok..before I found this site and looked into the proper techniques of insulation I started insulating our basement rim joist/sill plate area because we were working on the house and I was losing tons of heat in this area. I insulated about 30′ of the sill plate area with foil backed 3/4″ JM insulation doubled 1.5″ against the 8×8″ sill beam. I later installed 1.5″ EPS along the top of the rubble foundation but I’m getting ready to add some wall insulation against the rubble wall and build a wall in front of that…but if I have to tear out this foil back insulation I’d rather do it now than later when it’s harder to get to. I’m concerned that condensation may form between the insulation and the wood sill plate and the condensation then prevented from drying to the inside because of the foil backing. Any help would be appreciated. Thanks

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  1. user-2423385 | | #1

    Sorry..this is a rubble foundation 1880 construction in Norther Wisconsin. The foundation is about 2' above grade and 4' below.

  2. GBA Editor
    Martin Holladay | | #2

    For most homes, your insulation approach wouldn't raise any concerns. Here's a link to an article on insulating rim joists: Insulating rim joists.

    In your case, however, there is a small concern arising from the fact that your house probably lacks a capillary break between the foundation wall and the sill beam. (Most modern homes have closed-cell sill seal in this location, and the sill seal acts as a capillary break.)

    Because of the lack of a capillary break, your sill beam may be absorbing moisture from the foundation wall. As long as this beam dries out regularly, it can stay sound for decades. If drying is impeded, and the wetting rate exceeds the drying rate, the sill beam can begin to rot.

    Don't panic, though. If your basement is relatively dry, your sill beam may not be at risk. The fact that the wall extends 2 feet above grade is in your favor. If the rubble wall and the lower portions of your wood-framed wall are exposed to sunlight on the exterior (rather than hidden by shady bushes), that also helps.

    One way to address any concerns is to raise the sill beam with a jack so you can slide a capillary break under the sill. A few people have done this, and it isn't as hard as it sounds.

    Another way to handle your concerns is just "watchful waiting." You may have no problems at all.

    I would be in favor of leaving the rim joist insulation just the way it is.

  3. user-5406553 | | #3


    If you're interested in the "all-in" approach to your basement, check this out:

  4. user-2423385 | | #4

    Yes...I looked at that a few times and I've been all in like that on the rest of the house, I may get into that in a few years by digging the basement down and insulating the floor but i would have to step out from the foundation perimeter and then dig down as I wouldn't want to chance a stone wall crumbling, even though I doubt they could move easily as they have been there for 135 years and are almost two feet thick. I'm staying clear of the whole spray foam thing as it's so cost prohibitive and I'd still have to build the walls around the interior if they are going to be useful. Thanks much

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