Making windows
How-to, not how-should
I was fielding questions on Instagram this week and a number of folks asked about window construction on the latest cabin, so I figured I’d do a deeper dive here.
The Basics
The new cabin has 11 windows. I made the 9 non-opening windows. The two sliding windows came from a local window and door shop. (They also fabricated the exterior french doors; the interior wooden door I built in my shop.)
I don’t know what I’m doing. I did some things right. Some wrong. Some stuff unconventionally. But I took the opportunity to experiment and put a lot of thought into possible water intrusion. So there’s that. (More on that approach and general ethos at the end of the post.)
Eight Upper Windows
The standard way to do windows would be to build them in a shop, then install them into rough openings with flashing, shims, and trim. That felt complicated (and I wasn’t into reducing the window size further) so I built them right into the framing.
First step was flashing the sill with some galvanized metal and tape. Ideally this would all be sloped outward, so any water that works its way under the sill will drain out (we did this on the lower sliding windows) but I didn’t want to build the sill any higher than necessary, and rationalized that these sills were tucked up under the roof enough where sufficient sealing would likely eliminate any water penetration. We’ll see how that theory pans out!
Next was installing the sills. I made them in my woodshop, and those are sloped. And oiled. They extend over the metal flashing with a shallow drip edge cut into the underside so that water drops off, rather than wicks underneath. These were screwed down atop a very heavy dam of Sikaflex sealant.
The first layer of wood strips were then installed which would hold the glass in place. These were attached with finish nails and—you should see this coming—a generous bead of sealant underneath.
Here I started building out the posts and upper framing with redwood scraps to meet the plane of the siding below and then paused to finally take some glass measurements.
As expected—and the reason I waited until the framing was complete and the sills were actually installed—they were all a little different. I opted for ⅛” single pane glass, undersized by about 3/16” on the sides and top. A local glass shop cut them, and I paid a small premium for the non-square angles, bumping the glass cost up to about $500.
When installing the glass I made sure to use clear window silicone, as it would probably be visible. I laid a bead all the way around, seated the glass in place, then added another bead atop to fill in around the edges.
Finally, exterior pieces were installed over the glass, locking the panes in place. These were attached with finish nails and—you guessed it—an extremely hefty serving of Sikaflex .
With the windows built out, I taped off edges to lay down a final crisp bead of that sweet sweet dark bronze Sikaflex. Note I didn’t trim out the bottom of the window, figuring it best to let water shed right off.
The sealant was smoothed with a wet finger, the tape peeled off, and the windows were done.
Front Window
This window buildout was bound to be weird. I had this image in my mind of a slice of glass, bisecting the siding, top to bottom. Figuring a way to do that, without adding framing and heavy trim, was tricky.
The cabin facade ended up as two layers of siding with a water-resistant barrier in between. To achieve the look I had in mind, I figured I’d recess the glass into the first layer of tongue and groove, seal it into the water barrier, then lay the exterior cladding over it.
Step one was to measure and order the glass. I went with ¼” tempered, sized to overhang the framing by ½”. Next, I traced its outline and routed out a slightly oversized pocket so the glass would sit flush. At the top and bottom, where the window crossed the floor joist and the wall framing, I installed planed strips of knot-free old growth redwood, as these would be preserved under the glass, like museum displays.
I found some correctly sized right-angle metal brackets and installed them along the bottom edge to support the glass. I also added small strips of rubber so that the glass wasn’t sitting on the metal.
The glass went in with Sikaflex, though not so much as to squeeze out and be a cleanup issue. Then I filled in any gaps and added a bead over the top and gave it 24 hours to cure.
The next day I put down a layer of flashing tape, then another that would seal the water resistant barrier to the first tape layer. At this point, the glass was now one with the Hydrogap and roughly as watertight as the rest of the building.
The final step was lapping exterior siding over the tape and glass, but this gave me pause—if you’ve ever lined up individually cut boards you may have found that the edges never really align quite right. On a deck I’d tackle this by snapping a chalk line and cutting all the deck boards at once, but I couldn’t very well do that with my siding right on top of the glass.
Here’s the solution I landed on (and sadly never photographed):
I stuck a straight-edge scrap aluminum to the window with double-sided tape. Then each piece of siding was test fit against the aluminum (and re-cut several times) to ensure it sat tightly and perfectly parallel to the metal edge. When the aluminum was peeled off, the siding looked like it had been cut in a single pass.
Nailing that siding at the window edges was nail-biting. I measured where the glass was believed to be underneath, and had to drive a nail in just past that, at an angle, to seat into the framing. If I hit the tempered glass, it would shatter, and all the work would be for nothing. I pre-drilled to better my chances and 48 nails later the job was done. Mostly…
My hope was to leave the window just like that. No trim. But I found that the gaps in the end-grain of the siding were unsightly and I could see some flashing tape when standing at just the right angle. Plus I knew some trim over the end-grain would be better for the longevity of the wood. So I ripped some 3/16” micro-trim for the exterior and interior of the window.
Interior trim was installed entirely with wood glue and clamps. Exterior was done with Sikaflex and trim nails.
Dos and Don’ts
Was any of this the “right” way to do this? Probably not.
We’ll see how it fares over time, though the windows have weathered a number of storms and so far I can’t spot any leaks. I’ll concede that some additional sealing could be added; I stopped short of applying caulk and paint or oil onto every spot that could have benefited. And if that front window ever needs replacing, well…
But, I will say that through every step of the process I was considering how water would flow, wick, or get blown, and where it would likely wander as it inevitably snuck past a layer or two of redundancy. I was also pushing the boundaries of my comfort and skills, and trying some ideas for the sake of the fun experience and learning. Which is to say, I can’t vouch for the techniques, but I absolutely stand by the process.