Sealing the Attic plane
I am going to blow cellulose into the attic of my new home. I had air tight IC can lights installed, but how about sealing the other electrical appliance penetrations? Can I use the canned foam, for instance, around the place where ceiling fans will hang? It says good to 240 degrees. Is ANYTHING up there going to get THAT hot? There are electrical boxes up there, and of course you can see through the zillion holes in them. What’s the best way to seal them–do you just cover totally with foam? I think the penetrations of worry consist of electrical boxes, fan light mounts/electric, and bathroom fans. All the other plumbing and conduit penetrations in the walls got done with foam earlier.
The house was built with 2X10 joists in the attic, all the way to the exterior walls to allow for full insulation to the edge. Any other tips before I dive in? Thanks!
You don't want any foam to get inside of the electrical boxes.
While foam is good for sealing a lot of the smaller holes, to protect a box, even a can light (especially non-IC lights), you might want to consider making a small box from rigid foam board insulation.
I use scraps of polyisocyanate insulation left over from other projects.
Cut the five sides, then use a bead of canned foam on the edges as required, then fit the box together. The foam will act as the glue. If you have trouble keeping it all together, use duct tape (ta da!) to hold the pieces together while the foam hardens.
You can then run another bead of foam on the open adge of the box and "glue" it to the attic side of the drywall, covering the electrical box.
If the boxes will be covered with blown cells, you can mark their locations for future access, or so you know where not to step, with small landscaping flags. Stick the wire flag right into the foam box.
Foam is good around edges of boxes, though some inspectors are requiring firestop caulk for this sort of thing now.
I use cheap siliconized latex caulk to seal holes in the box itself. You could use butyl, or poly, or silicone, but these are messier, smellier, and more expensive for no benefit that I can think of.