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insulate rim joists from above?

esfahlgren | Posted in General Questions on

Hi there, 

We’re continuing to make improvements to our zone 5A Michigan 30’x30′ 2 story home built in 1988.  Next up is updating the basement for the kids to have a play area and insulate the rim joists to help with air sealing and overall insulation goals.  The problem is that the kind previous homeowners already finished 75% of the basement with drywall to ceilings and walls.  In the interest of small, continuous improvements, we’re thinking that we might tackle the insulation of the rim joists when we replace the flooring in the main level of the home.  Has anyone ever done this or have suggestions?  It seems like we could saw out an access port from the subfloor, insulate each bay with rigid and canned spray foam, then use the same offcut to seal up the subfloor.  That seems much easier than dealing with all the drywall and also less wasteful.  What do you think?  Next spring, we’ll tackle exterior insulation and siding so we’ll have a second shot at air sealing from the outside.

Thanks for your wisdom!

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  1. jadziedzic | | #1

    Drywall is easy to cut out, easy to replace, and (for a professional and some do it yourselfers) relatively easy to finish. Just remove a foot-wide strip of drywall parallel to the rim area in the basement ceiling, insulate, and replace the drywall. Finish (tape & mud) it yourself or hire a pro. In the end it will much less hassle than hacking up the subfloor and replacing it - plus you'll get the job done a lot quicker, and probably do a better job in the end.

  2. Axelkeitz | | #2

    Like stated above, unless you are planning on replacing all of your subfloor I wouldn't cur a ton of little holes in it. All those little holes will be squeaky in a couple years no matter how you secure them. I will second cutting the drywall. Get as much ridgid foam in there as you can while you have it open!

  3. Expert Member
    BILL WICHERS | | #3

    It's not uncommon for subfloor to extend under the bottom plates of the walls, which can complicate things since you have to cut "all the way around" your access openings, and you have to get up tight to the walls. You'll also have issues on the sides of the basement where the joists run parallel to the wall. While it is possible to insulate from above, in this case I think it will be pretty difficult for you, and you'd be dealing with a structural element (subfloor) instead of a mostly cosmetic element (drywall). Structural work is more critical for safety.

    I would open up the drywall in the basement and insulate in the usual way. If you want to do this as a DIY project and you don't do a lot of drywall work, I suggest you just hang new new drywall but have a contractor mud and tape everything. Experienced drywall finishers can go much faster, and do a better job, than someone who doesn't do a lot of drywall work.


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