Friday, April 10, 2009

Dormer Window Installation

I thought I'd go ahead and install the window in the dormer I just finished. As before, I've used a peel-and-stick window flashing to seal the opening against water penetration.

In a post I did back in mid-December, I described installing windows in the dining room. Those windows were installed in an ICF wall. ICF walls are not covered with housewrap, so for those windows I needed to use a primer to get the peel-and-stick flashing to stick to the styrofoam. However, the dormers are constructed of lumber (not ICFs) and are therefore covered with housewrap. When installing windows into housewrapped walls, you don't need to use a primer because the peel-and-stick flashing will stick to the housewrap by itself.

So, to install this window, I first covered the wall with housewrap. The housewrap is then cut and folded inside the window opening on the sides and bottom. The top flap of housewrap is folded up on the outside and taped temporarily to keep it out of the way. Then the peel-and-stick flashing is applied... first the bottom, then the sides, then the top.

I put the window in the opening and tacked the bottom in place loosely with a couple of nails. Then I tilted the window out and held it in place with a piece of cable. This holds the window away from the wall so that I can put a bead of silicone on the flange on the sides and top of the window. The bottom edge is left unsealed so that if any water does get through the window frame itself, it can drain out the bottom between the flashing and the window.

I put a 1/4" bead of silicone on the inside of the window flange and then tilted the window back into place. I checked for level and then nailed it into place. Any silicone that squeezes out is just wiped off.

Once the window permanently in place, I put the final layer of peel-and-stick flashing over top the window flange on the sides and top. When that's done, the top flap of housewrap is then brought down over top the flashing and taped into place. All of the seams and edges of the peel-and-stick flashing are also taped.

That's it. Hopefully the only way this window will ever leak is if I leave it open during a storm.

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