Insulating and Air-Sealing Rim Joists in Balloon Framing
Hello Everyone. I recently purchased my first home which is a 1930-built balloon frame. I’m looking for advice and guidance on sealing the perimeter at the foundation walls.
I do not have a “built-up sill” as shown in this image: https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Balloon_frame.jpg/300px-Balloon_frame.jpg What I have instead is simply horizontal exterior sheathing boards so from the basement side you can reach your hand up into the stud bays. Previous owners of the house blew in insulation into these bays and let it fall down to the sill plate, simply blocking it off with cardboard stapled to the face of the studs and floor joists. The photo with the white wiring shows what this looks like after the cardboard is removed. The photo without the white wiring shows what it looks like with the insulation removed – you can see the external sheathing to the left of the stud (for whatever reason, there is original blocking at floor level here so the insulation doesn’t extend down to the sill in this bay but this is an exception). One challenge is that the studs and the joists seem to be at irregular distances so there is no consistency in stud/joist placement.
I had a blower test done and as expected this was a big problem area so it needs to be sealed and insulated. I’ve been trying to figure out a good way to do this and came up with the attached detail. It’s labor intensive but I think it will get the job done properly. But before I start, I wanted to run it by this forum and get some feedback. The idea is to work joist-bay-by-joist-bay, remove the blown-in, clean it out with a shopvac, and cut 1″ vertical facing foamboards to fit between the stud and adjacent joists. I would then add Great Stuff Pro to the joint between the wood sheathing and the sill plate and the horizontal seam between the runs of sheathing (there’s a seam about 4″ above the sill that you can make out in photo where you can see the sheathing). I’d then insert the facing foamboard so it seals in place as the Great Stuff cures. Next I’d have another piece of foamboard cut and notched around the stud that will serve as horizontal blocking for the stud cavity insulation. This piece will be supported by the facing foamboard on the exterior side and by a support that I can nail to the stud face on the interior side. This piece would be installed and sealed all around with Great Stuff Pro. After it cures, I’d beef up the insulation with 6″ of fiberglass which would bring it to the edge of the sill plate. All done. Sealed and insulated. I’m attaching a photo for a trial run so you can see what I’m proposing. Sorry about the photo orientation – they’re automatically rotating when I upload and I can’t straighten it out.
So how’s that sound? Any thoughts/comments/feedback?
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