Timelapse: Insulating the roof

Got our first layer of our roof insulation sandwich in place. See Brian’s earlier posts for more on our insulation strategy: this polyisocyanurate foam (R Max) will be combined with rock wool to give us a total of R-28 in our 2×6 roof while still maintaining an air channel to vent the roof.

Once we got the foam tacked up, I got to whip out one of my favorite tools: the foam gun. When I first bought this guy during my home reno a few years ago, we opened the package and Brian started to say, “I like that it looks like…” To which I may have responded, “Han Solo’s blaster!” and then run around the house making “pew pew” noises)

A substitute for the plastic straws that come on the standard cans of expanding foam, the gun takes larger cans as cartridges and allows for more accuracy in application: both in aim and flow control. They’re a little on the pricey side, so not necessarily something I’d recommend buying specifically for a build, but if you can borrow one they are great.

Today I foamed all the edges of the polyiso, which did the double duty of gluing the foam sheets in place and sealing all the air gaps. Good air sealing can make a world of difference in the efficiency of your insulation, especially in a small structure like this with thin walls and roof. We’ll pull the gun out later to seal the windows, backs of electrical boxes, and any other penetrations in the building.

I was especially glad to have the control of the gun up in the ends of the roof, where it was important to ensure that extra foam didn’t expand upward and block our roof venting. Foam seams like a no brainer to use, but if you’re not careful it can get away from you – as I learned the hard way once trying to fill the cavity of an old window weight well. They call it expanding foam for a reason, and it continued to expand and spew out of a hole in the wall for about 20 minutes while I watched helplessly. There’s a reason it says “not for use filling wall cavities” on the can!

x Liz

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