Need to insulate my balloon frame "rim joist" area

Old 01-10-22, 03:59 PM
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Need to insulate my balloon frame "rim joist" area

Hey everyone,

I've been soliciting ideas from all over about this project and figured I'd give here a try.

I own a 1930s 1.5 story home just outside of Baltimore. I've noticed my kitchen floor is typically very cold so I went into my basement and began inspecting the rim joist area.

Low and behold, the old insulation in this area was pretty poorly installed and not only that, it's a balloon frame construction so there is a large void into the stud bay above.

You can see in the image below that the white wire is running across the subfloor and into the void/stud bay above.

The walls above are insulated with mineral wool batts. This is a section where I pulled out some older mineral wool that was poorly cut and thrown in there.

I'm trying to figure out what the best way to seal this area up is AND add fire blocks.

My current plan is to cut 2x4s to fit against the wall so that a fire can not quickly travel up into the stud bay above through the open gap. As for insulation, I'm torn..

1. Buy one of the dual spray foam kits and spray the space.

2. Fit rigid board into the gaps and spray foam the edges.

3. Place mineral wool bats into the void.

I'm leaning towards buying the spray foam kit, but was curious of any opinions. I was originally worried about needing a vapor barrier but I am in climate zone 4 and it seems like that's not as big of an issue around here?
Old 01-11-22, 05:00 AM
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With all the odd shapes you'll have to deal with I'd use spray foam. I would search for a bulk applicator for fire blocking foam so you don't have to use disposable aerosol cans. Hopefully you can kill two birds with one stone and get your fire blocking accomplished with the foam. The spray cans can work but would be slow and expensive and having to hold the can upside down in that confined space won't work very well. You can put some tubing/hose over the rigid plastic applicator tube to extend your reach and allow you to get up into the joist bay while still holding the can upside down.

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