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Expanding Foam Between Two Floor Joists Over Concrete Foundation Wall

Expanding Foam Between Two Floor Joists Over Concrete Foundation Wall


Old 07-21-16, 11:23 AM
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Join Date: Jun 2003
Location: Canada
Posts: 164
Expanding Foam Between Two Floor Joists Over Concrete Foundation Wall

I will do my best to explain my question, here goes... Cold Canadian climate!

Our floor joists run east-west. I am applying spray foam for our basement rim joists (at the ends of the floor joist on the east and west ends of our house.) This is a fairly east task, see this pic, these I understand how I can simply spray foam these areas:

My question is about insulating the south and north areas where the floor joist run parallel to the foundation wall (see pics): This one is in our unframed laundry room:

These two is from our framed rumpus room:

The outside joists run directly above the concrete wall (Joist "A" in the pic below) and I believe there is another joist outside this joist (Joist "B") and a space between them. Should I drill a hole in the inside joist "A" and insert expanding foam inside this cavity between the two joists? I believe the cavity isn't insulated but is directly below the outside walls of main floor above it. I hope I am clearly describing my situation. I was planning on drilling an inspection hole and inserting my inspection scope into the cavity (that I think exists) so I can assess what I have.

Any comments/advice/suggestions would be appreciated. I hope I am clear in what I'm asking.
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Old 07-21-16, 03:06 PM
XSleeper's Avatar
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Join Date: Dec 2004
Location: USA
Posts: 20,534
What you are calling "joist a" is called a sill plate. Yes there is obviously a space on the other side of "joist c"... between it and the rim joist (what you are calling "joist b" is the rim joist) it is about 6" or 7" away and sets on the outer edge of the 2x8 sill plate... you don't need to drill any holes or get a camera to figure that out. About all you can do there is blow it full of cellulose. Probably would need to cover that gap with something as you go along so that it doesn't all come blowing out that gap.

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