Installing windows in T-111 siding

[DT]

What's the best way to install a new construction window in T-111 siding? If you just place the window against the siding you have all the grooves leading underneath the window flange on the top and bottom. I don't like the idea of just a caulk to seal things well, although maybe that is the practice.

I was thinking of trimming the rough opening with a 1 x 4. The T-111 would butt against this and the window would seal against the face of the 1 x 4. It still leaves you with lots of butt joints to caulk around the 1 x 4, but at least no grooves leading underneath anything.

-- Dennis

[HerHusband]

Dennis,

We used a rough sawn plywood on our house, basically T-111 without the grooves. I applied caulking under the window flange, then again around the outside of the flange. We then used 5/4 cedar to trim out the window, and that too got caulked. So, there are basically three layers of caulk as protection. Not the ideal situation, but there aren't any good solutions when you can't overlap the flange of the window.

One option I heard a few years ago was to use a circular saw and a straight edge to cut an angled slot above the window (45 degree's, sloping down so water can run out). Install the Window, then tuck flashing up into the groove, overlapping the flange of the window. You could probably cover that with trim and caulk to make it look better.

Of course, that only works with a square window. That approach wouldn't work very well with our arch top window.

Good luck,

Anthony

[SteveF]

If the siding isn't up yet, put the window on first. If it is, I would paint the T1-11 first, then install the window, put on rubberized window flashing (the peel and stick kind) on each side and the top (in that order) and finally install Miratec for trim. Leave 1/8" gaps between the trim pieces and between the trim and window. Caulk with silicone if you are not going to paint and polyurethane if you are.

Steve.

[HerHusband]

That's a nice situation for the top of the window, but the side and bottom window flanges would end up under the siding. Wouldn't any water running down along the edges and bottom of the window end up behind the siding?

It's also easier to install windows after the wall is built, and makes window replacement easier in the future.

Anthony

[SteveF]

Water running down the face of the window should drip off the end of the sill. There shouldn't be much water coming in from the side although the sides should be caulked and covered with flashing membrane in the same manner as the top.

Replacing the window some decades down the road would be a little easier if the window was on the outside of the T1-11. Saves the work of slicing the plastic nailing flange off first.

Steve.