Is spray foaming the garage ceiling enough to stop the bedroom from freezing?

I fixed this exact same layout in my last place, and the biggest mistake people make is focusing only on the R-value while ignoring air infiltration. The reason that bedroom feels like an ice box is probaly because cold air is moving trough the floor joists. If those joists extend from the garage into the rest of the house, you need to install solid blocking and seal it with spray foam. Otherwise, you're just insulating a wind tunnel.

Since you've got it down to the studs, go with **closed-cell spray foam** on the ceiling if it's in the budget. It acts as an air sealer and vapor barrier all in one. If you want to save some cash, use 2-inch rigid foam boards cut to fit the bays, seal the edges with a pro-grade foam gun, and then pack the rest of the cavity with **Rockwool**. It's much better for sound dampening and fire resistance than standard fiberglass batts. You'll thank me when you don't hear the garage door opener every morning. For those shared walls, you don't want a vapor barrier on the garage side. In most climates, the barrier belongs on the warm side of the wall. Since you're working from the cold side, use unfaced insulation so you don't trap moisture against the studs. And definatly wrap those copper pipes with foam sleeves while you have access. It's cheap insurance against a burst pipe if the garage gets exceptionally cold.

When you go to hang the drywall, you absolutely must use **5/8-inch fire-rated drywall** (Type X). It’s usally code for any wall or ceiling that separates a garage from living space. Don't just slap it up; use fire-caulk around the perimeter and any penetrations like light boxes or pipe exits. Sealing the drywall to the top plates is what acutally stops the exhaust fumes and cold drafts from seeping into your bedroom.

That blocking part sounds tricky. If I'm looking at the joists, how do I actualy tell if they go all the way trough? I don't want to miss a spot and end up with that 'wind tunnel' effect you mentioned.

Also, for the Rockwool, do I need to wear a mask or anything special? I've heard fiberglass is itchy as heck, but I wasn't sure if the stone wool stuff is any easier on the skin for someone doing this for the first time. I relly want to get this right so my feet aren't freezing every morning.

To tell if those joists go thru, look for where they disappear into the shared wall; if you feel a draft or see gaps around them, they're open. Also, wear an N95 and long sleeves for the Rockwool. It’s less itchy than fiberglass but the dust is still nasty. Make sure you hit the rim joists too. That's the perimeter where the floor meets the outside wall. If you don't seal those gaps, you're leaving a massive thermal bridge. I’d also check the R-value of your actual garage door. If it’s just a thin sheet of metal, that garage will stay a freezer no matter how much you pack the ceiling.

While you've got the ceiling open, don't forget the electrical boxes. Use some fire-rated putty pads on the back of any outlet or light boxes in that shared wall. It helps with the soundproofing, but more importantly, it keeps the exhaust smells from drifting up into your bedroom.

Also, check your actual garage door. If it’s just a thin sheet of metal, all that nice insulation in the walls is fighting a losing battle. Getting a door with a high R-value makes a massive difference in how hard the ceiling insulation has to work to keep that floor warm.