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Insulating Floor Joists over old stone foundation

My wife and I live in a home built in 1894. A serious amount of air infiltration occurs between the stone foundation and the rim/floor joists. On cold days (think -30 degrees), you can feel the cold air flowing in.

Insulating this area would normally be straightforward, but the stone foundation is 18-24 inches thick. This means that on the sides of the house where the floor joists run parallel to to the outside wall, in addition to the rim joist that aligns with the outside of the foundation, a floor joist (that is about 16" away from the rim joist) also sits on top of the foundation. This creates a highway for cold air along the wall.

We had the foundation tuckpointed, and this helped some.

To complicate things, the exterior of the house is stucco, and the rim joist is, of course, covered with stucco.

To stop the air infiltration, it seems that I need to do something with the air space between the rim joist and the adjacent (16" away) floor joist. But there is not good way to get to this space, as it doesn't seem reasonable to go into the outside stucco wall.

I've thought of drilling holes from the basement side of this floor joist every so often and putting some type of foam insulation into the space between the floor joist and the rim joist. That would be a lot of cans of spray foam, and there has to be a better way.

I am looking for suggestions on addressing these air infiltration issues. Hopefully there is a solution that does not involve restuccoing the house.


-- Bruce Leasure
Saint Paul, MN

Re: Insulating Floor Joists over old stone foundation

Often times the best way to find solutions is to call in a pro for specific advice and a bid. Go around with them as they look at the job and ask how they propose to do it. Most will give you a estimate for free and you're not obligated to use them, but now you will know how to approach the situation yourself when they leave!


Re: Insulating Floor Joists over old stone foundation

is there any specific type of wood/other material that may be most suitable to use with stone? like, depending on how porous it is, how much it expands or whatever.

Fishfool @ The Reef Tank

Re: Insulating Floor Joists over old stone foundation

In your situation, I would go for the spray foam insulation applied through holes drilled in the inboard joist. However, I would try to find a spray foam contractor rather than trying to do it myself with spray cans. It can be tricky getting that stuff to fill a blind cavity and you want someone with experience doing it. Also, if you get too much foam into the cavity it can exert enough pressure when it expands to do some damage. It might be difficult to find a contractor willing to take on this small a project but perhaps you can find one working in your area who could squeeze it in.

The foam has a significant air-sealing effect.

Be sure to drill the holes at the mid-height of the joist since this weakens it the least.

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