With the prep work for the radiant heating complete, we can focus on getting the windows and doors installed. I came up with the plan a while ago after reading up and watching some Building Science materials. The first was the back window in what will be the office. It’s the only double hung window, but the reason I decided to do this one first is that it opens onto the enclosed porch. That meant it was easier to install and it was covered in the event we ran into snags.

Original window removed

Original window removed

Sarah’s dad Mike, Rob, and Aaron helped me re-frame the window opening, moving it about six inches over to allow for the future stair landing when we redo the back porch. We mended and sistered a stud that became one of the king studs and put in a proper header with ½” insulation separating the 2x6s. This resulted in a somewhat ridiculous 8″ of solid framing in the wall. Good thing we’re putting on exterior insulation! Then we installed new sheathing in the closed up portions and cut back the siding around the opening, then caulked all of the seams.

The next step was to build the plywood box that extends out from the exterior wall so that the window was properly supported on the outside after we add two inches of foam. We added the Tyvek house wrap to the sheathing and then the glued on two 1″ layers of polyiso rigid insulation, ensuring that the seams didn’t align and taping everything with Tyvek tape. Normally these would be attached by screwing furring on, but the siding is a long ways off and we’re planning to use metal furring strips that we don’t have yet.

Re-framed opening

Re-framed opening

We added clapboard at the bottom to slope to the outside and installed a WeatherMate drain pan  on top of it. Next we used flashing tape along the sides and put the window in place with shims at the bottom. We secured it with straps on the outside face that were screwed through the foam and into the studs. I’ll need to finish the interior with some Great Stuff and backer rod. I’d like to thank Mike, Rob, and Aaron for their help and their patience with my non-traditional window installation!

Completed window

Completed window

This window was kind of a prototype, so I have a few lessons learned. First, the project took all day for the single window, and we had three people working on it. I need to streamline the process for the remaining windows. Some of the time was because we hadn’t done it before, but I’m also hopeful that if I pre-cut the material (studs, foam, plywood), I can install them faster.

Window sill detail (Credit: Building Science)

Window sill detail (Credit: Building Science)

Next, I’m a bit confused by a couple of details of the Building Science plans. First, their instructions leave the entire window sill area (highlighted above) effectively un-insulated, though it is air sealed and drained well. I think in future windows I’ll use spaced shims rather than beveled siding so I can fill the space under the pan flashing with expanding foam.

Window head detail (Credit: Building Science)

Window head detail (Credit: Building Science)

Second, considering how thorough the plan is when it comes to water management, the plywood extension box seems strangely left out, particularly at the top (highlighted above). The house wrap is underneath the foam specifically to handle water that might get inside, but the water is then directed onto the exposed plywood and trapped there because the foam is taped to on the outside of the plywood. We wrapped the corners of the housewrap to the plywood with Tyvek tape, but I think I’ll wrap the housewrap over the plywood at the top for the rest of the windows to create a better drainage plane. I may even try to add a slope to the sides so the water can continue to drain down the wall, but we’ll see how ambitious I get.

There are six windows to go: three along the side and three in the bay in the front. We also have the front door and the back sliding door, though the back sliding door will have to wait, since the porch stairs are in the way. We’re planning to install the door next weekend and hopefully I can get all the windows in the following week. Wish us luck!

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