Insulation at rim joist of basement wall

My father in law had an energy audit with a rebate program in Colorado. He is looking to improve insulation/seal of rim joist in basement. We don’t have many basements around here, so I am not sure what is the best way is for him. I suggested spray foam, but that was too expensive. So my next thought was 2 inch R board cut to fit and some can spray foam to seal in place. Any concerns on trapping moisture? Is there an easier way? Thanks for any advice.


When you add your time into what ever method you chose .
Spray foam might be the quickest and easy way to go.
The large cans cut down the cost. Any trapped moisture should slowly dissipate

Does Colorado have vapor barrier on inside?
Cheapest would be to fix the insulation and seal with vapor barrier/ acoustical sealant.

Rigid with foam to seal is a lot of work, but should work.

Keep in mind if the basement is not going to be finished , foam needs to be covered by a flame retarder. Drywall on ceiling accomplishes this, as does roxul insulation in the joist cavaties if being left unfinished.

Did my rim joists a few years ago with some scraps of 2" rigid. Put in rigid cut tight to fit, 3 1/2" fiberglass and 1/2" drywall and calked all edges. All leftover products done now and then when I had time to kill. Made a difference, also kept stuff from the landfill. Not well planned or scientific but its working well.

I have one spot I couldn’t access about 24’ long, I’m doing that with loose fiberglass shoved in the cavity with a paint stirring stick. Better than nothing.

Is the basement conditioned? I’m assuming so because it’s for a rebate program.

I’ve never had anyone put poly board in the conditioned space, we always do it from unconditioned space (exterior). So I’m not sure but I would make sure to seal it on all 4 sides so you don’t get conditioned air between the poly and framing; you could produce a place for condensation if conditioned air can infiltrate between the two and mix with exterior unconditioned air. But like others have said you may need to fire proof it since its on the interior. That method should be pretty fast and if done properly it should also help reduce the infiltration on the building.

He is retired and has plenty of time. Space is conditioned. Would it be better to remove bat insulation, install rigid with some expanding to hold in place, and then put insulation back. This would prevent any moisture issue. Dow makes a product thermax that I believe will meet fire issue.

This is what I did Glass insulation Cut dry wall to size and a handful of Compound . No air can get by

Should be able to write off the cost of the spray foam as an energy upgrade…no? At that point, it makes spray foam much more cost effective.

I did use Thermax pieces and then pink rigid, anything I could get my hands on excluding polystyrene.

My home was built in 1957 so I’m not concerned about the moisture being a problem, especially not in Minnesota. Exterior insulation would be better if I wanted to dig up my yard, but that isn’t cost effective.

I like the idea of placing the rigid on the exterior but with I joists it would be fun to fir it correctly. Using the spray foam does two things. First it is a great insulator but secondly it is also a vapour barrier. Almost every new home is done this way as it does cut down on the labor cost.
If your father in law has lots of time I would install the rigid at the rim joist and then seal it with foam as you have said. I would then reinstall the batt insulation and put your vapour barrier in front of it. If you don’t, you could trap moisture behind the batt insulation causing mold and mildew.