I have 2-inch insulation bats from when the house was built in 1976. Is it alright to caulk the joints where the joists meet the header boards before the insulation goes in place? Is rigid foam insulation better than fibre glass for this job? If you recommend rigid foam sheets, can I install a bead of caulk against the inside seam where the foam meets the joists and the ceiling? If you recommend fibreglass I can install a vapour barrier and join it up with the existing barrier.
Answer:
There is no need to caulk the joint where joists meet header boards. If there is to be caulking at all, I'd rather see it where the foundation wall meets the rim joist plate. My recommendation for basement insulation is always bats because they cover more homogeneously and 6mm poly can be installed over it. Two inches of fibreglass insulation gives you a total of R-7 and that is by no means enough. I'd rather tuck that stuff up above the framed wall you'll be installing and then pull your frame 1.5" from the wall to permit at least 6" of fibrous bat insulation in there to within 8" of the floor.
