Spent the weekend air sealing my attic electrical boxes and learned a lot

I spent three weekends doing the exact same thing with 2-inch Dow Tuff-R board in my own attic. It feels like a thankless job while you're covered in dust and spider webs, but those boxes around the light cans make a massive difference in how often the furnace kicks on. I used a Pro-series foam gun instead of the disposable cans becasue it gave me a much cleaner bead around the base of the boxes.

One thing I noticed while I was up there was that the top plates of my interior walls were leaking just as much air as the fixtures. I ended up pulling back the fiberglass batts and sealing every single gap where the drywall met the wood framing. It was a slow crawl, but it stopped that wierd "ghosting" dust pattern I was getting on the ceiling. For your bathroom vent, defintely look into the insulated R-8 flex ducting. I swapped my old uninsulated aluminum pipe for the insulated stuff and used some foil tape to secure the vapor barrier. It stopped the dripping issues I had during the coldest weeks of January. It's tedious work, but you're definitely not wasting your time.

I actually went a different route because my roof pitch is so shallow that building custom foam boxes was a nightmare for clearance. I ended up buying those pre-made Tenmat covers for my recessed lights. They’re basically mineral wool hats that you just drop over the fixture and seal at the base with a bead of Great Stuff. It saved me hours of measuring and cutting polyiso, though they definitely cost more than scrap board. While I was up there, I realized the biggest leaks weren't even the fixtures but the top plates. I spent a whole afternoon dragging a shop vac and a bucket of fire-block caulk along every interior wall line. Every single spot where a 14/2 Romex wire poked through a drilled hole was a tiny chimney. It’s disgusting work, and I definitely recommend a high-quality respirator and some heavy-duty kneepads, but sealing those hundreds of tiny holes actually dropped my blower door score more than the light boxes did.

Don't forget the attic hatch while you've got the foam board out. I used my leftovers to glue a 4-inch stack of polyiso right to the back of the scuttle hole cover. Then I added some thick weatherstripping around the wood trim where it seats. Before I did that, my thermal camera showed a massive purple heat sink right in the hallway. Now it’s the same temp as the rest of the ceiling. It’s a ten-minute job that actually finishes the seal you're building.

This all sounds so intense. I'm just starting to look into my own attic and I honestly don't know much about what I'm looking at yet. When you mention sealing the top plates where the drywall meets the wood, do you have to move all the old insulation out of the way first? That seems like it whould take forever. Also, is there a specific type of foam that's safe to use near electrical wires, or does it not relly matter? I'm worried about accidentally creating a fire hazard while trying to save on my heating bill.

Back in the 70s, we didn't have these fancy polyiso boards or canned foam; we just stuffed oakum or extra rockwool scraps into the gaps and hoped for the best. You're doing it the right way. One thing people always miss is the plumbing stack. Check where that main vent pipe goes through the floor—ussually there's a gap big enough to toss a cat through. I like to wrap some sheet metal around the pipe first to bridge the gap, then seal it up. If you don't plug that 'chimney,' all your light fixture work is for nothing becasue the heat will just find the next exit.

Quick update—I used my leftover polyiso to seal the attic hatch like suggested, and the difference around that opening is huge. But I'm still struggling with those tight spots near the eaves where there’s barely room to move. For those of you who did the top plates, did you find a specific tool that makes clearing the old insulation easier?