I'm dealing with that classic bonus room issue where it's consistently 5-10 degrees warmer or cooler than the rest of the house. I've already had a spray foam company treat the knee walls, but I'm still experiencing temperature differences. I'm considering gutting the bonus room and having it fully spray foamed. Does it make a difference if the spray foam is applied from the garage ceiling or from the bonus room's subfloor? The garage has 14-foot ceilings, so it would be a lot more work to remove the drywall compared to just taking out the carpet and subfloor in the bonus room.
5 Answers
Focus more on insulating the ceiling and walls of the bonus room rather than stressing about the floor insulation. If you do want to insulate the floor later, you could always cut holes in the garage ceiling and blow in loose fill insulation from above instead.
I suggest using cellulose. Here's a simple way to do it: drill some holes in the garage ceiling, run a hose to blow in the cellulose, patch up the holes, and you're done! It offers better R-value than fiberglass and is easier than a full gut job. Plus, it has great sound dampening properties, which is a bonus!
Spraying up against the subfloor is typically the better route, but either approach will work. I also recommend spraying the cathedral ceilings and seeing if that improves the situation before worrying too much about the floor. If you've got carpet, it might not make a huge difference to spray the floor.
Honestly, I think going with fiberglass insulation would be a better option overall, but that's just my take. It gets the job done pretty well!
It shouldn't really matter as long as you make sure to get complete coverage. Both methods should work, just focus on sealing everything up!