Insulating Basement w/ Rigid Foam and Batt

Reilley · 10-22-2008, 01:19 PM

I'll be insulating my basement in the coming weeks to take advantage of the ecoEnergy grant program (Ontario). The walls are required to be insulated to R23 (on paper, I don't need to hear about "real world performance"). To achieve this value I will be using 1" rigid foam (R-5) glued to the concrete, followed by 6" batt insulation (R-20).

I plan on using 2x4 strapping/studding spaced two inches from the rigid foam which will allow the 6" batt insulation to be installed without squishing it. The strapping will be 24" OC. I don't want to use 2x6 as that would be overkill and a waste of resources. I'm going to build the walls in place in order to provide additional support to the floor joists above.

I'm going to insulate behind each 2x4 to fill the 2" gap between it and the rigid foam. Does any product exist that would fill this gap or am I going to have to cut insulation to fill it?

As for the header, I'm planning on using the same 6" batt with rigid foam cut to fit each joist space to seal it in place. Should I sandwich the batt with rigid foam or will caulking the sill plate to the concrete be sufficient on that side?

Does anyone foresee any issue with my plan?

Winchester · 10-23-2008, 10:36 AM

Quote:

Originally Posted by Reilley

As for the header, I'm planning on using the same 6" batt with rigid foam cut to fit each joist space to seal it in place. Should I sandwich the batt with rigid foam or will caulking the sill plate to the concrete be sufficient on that side?

I'm going to jump out on a limb here and believe you are talking about the rim joists? I'd put in the rigid foam first (caulking and foaming to seal as necessary) and then add your 6" batts.

Wish we had grants for such purposes. Best of luck.

Reilley · 10-23-2008, 10:46 AM

Quote:

Originally Posted by Winchester

I'm going to jump out on a limb here and believe you are talking about the rim joists? I'd put in the rigid foam first (caulking and foaming to seal as necessary) and then add your 6" batts.

Wish we had grants for such purposes. Best of luck.

That's a good point, thanks. The foam on the outside would serve as a moisture barrie. I'm going to sandwich the batt with foam on the inside as well just because it will be easier to seal to the floor joists.

Lansing · 10-26-2008, 02:16 AM

Sounds like you got this covered ok...Nice that you got this grant...

As your taking the 2x4 studs out 2" from the walls either use a strip of 2" foam behind the 2x4 or a strip of the batt...Note that open space will let you run your electic wires for power boxes, etc you may want in place...6 mil poly sealed on the warm side of the walls...Don't seal poly on the outside rim joist areas...The batts should be set in place first then cut 1" foam and cork it on the inside warm area...No moisture can get sealed in from escaping out this way...Good luck on your project...