Siding Prep

The last couple weeks have been fits and starts. Basically finishing up the exterior insulation and installing the strapping.

I used 3/4" plywood "straps" screwed through the foam into the studs. The straps serve as attachment points for the siding, which I will put on next.

Finishing the foam was a laborious process. All the seams of the foam had to be taped. If I couldn’t tape them for some reason, I had to fill the gaps with spray foam. This was important to make sure there were no air leaks (or at least as few as possible).

To give an idea of how meticulous the air sealing has to be, here is what I did to seal around the sewer cleanout. I first sprayed expanding foam, then waited for the foam to cure before I trimmed it and finished with tape.

I had to use 6" long screws to attach the strapping. It was a little nerve-wracking to drive these screws through thick foam, but I only missed a stud three times. I had to use a corded drill; the cordless drivers could only drive a few of these at a time before the battery power gave out. I almost overheated the drill, too.

At the top and bottom of the walls I had to put insect screening. Once the siding is on, there is a continuous air space between the siding and the foil-faced foam. The concept is called a “ventilated rainscreen“. The siding can be a little leaky; any moisture that gets behind will run down the foam and out of the wall, or evaporate. This improves the durability of the building by reducing water intrusion and extending the life of the siding and, in the case of the wood parts, its paint or stain.

The air gap also allows the reflective foil facing to serve as a radiant barrier. This is pretty important in a hot climate like ours. It reflects a lot of solar energy away from the building in the summer time.

This is the aluminum insect screen at the bottom of the wall. It wraps around the strapping. When the siding goes on, it prevents bugs and other critters from crawling into the air space between the siding and the foam.

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