69dartgt wrote:That would have been my first choice but the cost involved, whether you buy a kit to do it or have a professional come, is a bit prohibitive. Can't see there would be a whole lot of difference in insulating value between spray foam and foam board? Not sure.
There's the trick! I use both. I use foamboard when and where I can, then seal it up with the foam gun.
For rim joists- which I've only done a handful because I have wires and lots of other stuff that has to happen there first- I cut 2" thick foamboard with about 1/4"-1/2" gap around it, slide it in and hold it in place, then stick the tip of the gun in the gap about an inch and do my best to fill the gap, just the 2" thickness of the board, all the way around.
It makes an airtight seal, holds the foam in place nicely, and often leaves the wires BEHIND the foamboard, without being covered in foam.
My idea on that is when/if I need to access the wires, I can simply break the foamboard and pull it out. The Pro foam is not too bad to pull off and scrape from a surface, so it can simply be replaced after whatever work is finished.
Is it a perfect method? Nope. It leaves a gap between the rim joist and the foam. But I often make it up as I go and steal any ideas I think would be helpful
For walls, large sheets of 2" foamboard, covered with OSB, then foam gun seal all the edges and any gaps. Same with electrical boxes.
Cost wise, this is the best combination I've found on the foam side. Replacing fiberglass insulation between studs in walls and ceilings with new R13 (vs R11 thrown in many years prior with little care) and taking care to completely fill the voids and staple the vapor barrier continuously is the other part.
Results? The upstairs rooms we've completed (also has 3/4" pine tongue and groove run wide and horizontally to look like the interior of a log cabin) can be 70F when we go to bed and kick it down to 65F will often be 66F or 67F in the early am, WITHOUT any heat running in that zone for about 7-8hrs. This is down to about low 30's like we have now.
Maybe not "spectacular" results, but considering there used to be spots where we could see daylight (!) and running heat constantly had marginal results, it's a pretty big improvement for us.