Continuous insulation, window boxes, tyvek, and more!

Hey everyone! Since it’s been so long since I’ve updated the blog with any useful information, I’m going to give you all a massive photo dump & some explanations below — this should be really helpful in particular for anyone considering using steel framing! Steel framing is awesome, but it does come with some unique challenges that you should be aware of. Please see this former post if you’d like details on the framing itself!

Insulation

Because steel is a great thermal conductor, it really pays to use a technique called ‘Continuous Insulation.’ Basically, this means putting at least some of your insulation outside the studs, instead of putting everything between the studs as in typical wood frame construction. This is actually a great energy efficient technique for wood framing too, but it’s really essential when using steel.

We decided to put all of our wall insulation on the outside, leaving the stud cavities free for easy running of electrical, plumbing, propane lines, and even shelving in some key areas. Directly over the plywood sheathing, we applied 3″ of polyisocyanurate rigid foam, which has an R-value of about 6.5/inch. We did two layers of 1.5″ foam, layering the ends of the pieces so that no seams ran straight from the outside to the inside. All of the seams were taped with Tyvek tape so that the foam acts as an air barrier.

Window Bucks

At the same time we were adding the foam, we were building wood bucks for all of our windows. We wanted to do “outie” windows for a couple of reasons — 1) we’d have nice deep windowsills inside, which we love!, and 2) the flashing details are a bit easier. However, with the 3″ of foam, this meant that our windows wouldn’t be directly supported by the steel studs. Window bucks allowed us to “build out” the structural framing, giving our windows a strong place to sit. We used 2x8s, which provided a solid nailing surface for our windows (which have an integral nailing fin). They were also the perfect width to be flush on the inside of the framing and the outside of the foam (7.5″)! The only downside of the window bucks is their weight — we basically lost the weight savings we had from using steel instead of wood when we added these, since we have so many windows!

Housewrap

The next step was the Tyvek house wrap. This is a pretty straightforward, and we had gotten a great deal on a mostly full roll of Tyvek from Craigslist. By the last face of the house, we were cobbling together all the scraps we could find, but we had just enough to cover all the foam! Again, all of these seams were taped.

Furring

We used capnails to temporarily hold the Tyvek to the foam — but really, the furring strips were the piece that keeps the Tyvek in place. Ahh, the furring strips… these were a really interesting and challenging part of the plan. The purpose of the furring strips (0.75″ thick) is to lift the siding away from the house, providing an air space that allows for better drainage & evaporation of water that does get behind siding; this configuration is called a “rain screen.” The siding is then attached to the furring strips.

But in order to provide a strong base for the siding, the furring absolutely has to be anchored well, which means it needs to be directly connected to the studs. The studs are now under 3″ of foam and .5″ of sheathing — which meant that we needed really nice long, self-drilling screws! We ended up having to special order 5″ long #10 self-drilling screws, as these are not available at the local store. We were also worried about hitting the sheathing screws, so we did a crazy plan where we held each piece of furring up to the house before putting on any insulation, so we could choose where the screws would go. After the insulation and Tyvek, we had to measure very carefully to make sure each piece of furring was still aligned with a stud. This was even more complicated by us using both horizontal & vertical pieces of furring in different areas (the furring should be perpendicular to the siding direction, and we had a complicated siding plan)! Mostly, it went pretty well, but there were more than a few measuring mistakes as well.

Next post, windows & door!

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