We bought an older home that we use more as an office. The basement is totally uninsulated including the rim joists. Last winter, it got really cold down there to the point that the floors upstairs also were cold. So I know the rim joists need to be insulated cause they're exposed to the outside with only the siding and what looks like no insulation behind the siding (in the basement only).
If I only installed rigid foam on the rim board, would that make a substantial dent in reducing the cold or would that only be a drop in the bucket? I'm not interested in insulating the basement walls cause it's more an office than our home and it doesn't get down to zero every year but if it would make the basement just cool/cold instead of frigid, I'd be happy with that.