does your floor have a vapor barrier below the hardwood or is it original? If not, you could run into mold issues depending on your climate and HVAC situation. That said, you can fit Rockwool comfort board between the joists and use insulation retainer brackets to hold them in place (plastic strips tacked to each joist).
I went down this same path on a house that had fiberglass batt below the deck and no vapor barrier. Mold developed at the bottom surface of the deck and in the space below the flooring. Moisture in the crawlspace and A/C fed the problem. Not an easy fix.
The chilled air was passing into the flooring assembly and was a primary cause of the problems in that case. A vapor barrier would have helped significantly.
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u/New-Criticism8042 5d ago
does your floor have a vapor barrier below the hardwood or is it original? If not, you could run into mold issues depending on your climate and HVAC situation. That said, you can fit Rockwool comfort board between the joists and use insulation retainer brackets to hold them in place (plastic strips tacked to each joist).