How to flash sill on a flanged window?
SquakMtn
| Posted in General Questions on
I installed Anderson flanged fiberglass windows using 2X2 around the opening and then 1 1/2 inch polyiso outside of that so that it is flush with the 2×2. I will use 3/4 inch furring strips to develop the rain plane and then place 3/4 inch T &G cedar siding oriented vertically. So I am pondering on how to extend the sill past the lip of the window to divert water away to the outside of the siding at the window bottom because that edge is to the inside of the outside edge of the siding. Because it is flanged, how do I extend the sill to overlap the siding below and attach it?
Thanks,
Steve
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Replies
Steve,
If I understand you correctly, you have chosen to install your windows in a way that makes them recessed. It sounds like the recess is due to the thickness of your rainscreen strapping.
It's certainly possible to install recessed windows. (Some people refer to the location of windows in the wall by calling windows “innies,” “outies,” or “in-betweenies.” It sounds like you have chosen to go the “in-betweenie” route.)
All windows have a window sill. The window sill needs to be wide enough to shed water beyond the plane of the siding. If you have chosen to install in-betweenie windows, you need to install flashing or an auxiliary sill under your window to carry the water out. This flashing or auxiliary sill must be sloped; it should extend from the bottom window flange to a location that is beyond the plane of the siding. Ideally, it should include a drip edge or a kerf on the underside.
You need to plan this sill extension -- which can be made of cedar, PVC trim, or copper flashing over almost anything -- carefully. All of these details should be drawn up and planned before your windows are installed.
Steve,
When you mention the sill, are you referring to the bottom of the rough opening? I have designed these details before, but it's hard to know exactly what your situation is by the description. If you could provide a quick sketch of the issue, I think I could help.
Trevor
Hello Trevor,
I am attaching two views to illustrate. As Martin said, I need to extend the sill from the window to allow water to be diverted over the face of the siding. As it is presently, the distance from the face of the flange to the outside of the window is 1 1/4", while the sum of the furring strip and siding is 1 1/2". I wanted a modern style trim and preferably with metal, rather than the traditional wide wood trim most contemporary homes have. I have looked for dark brown flashing at the stores in stock and haven't seen what I want. Any suggestions on developing this detail?
Thanks,
Steve
Hi Steve- I will sketch you up something this weekend and post it here. It will involve getting some custom made aluminum flashings to match your windows - I often get this type of work done by my siding/soffit/fascia guy who can whip up some custom bends on his break for a reasonable price.
Trevor
Steve- Hopefully these quick sketches help. The top and bottom flashings need to be sloped. You could use the bottom flashing profile for the sides if you wanted, or a 90 degree bend would work too. You will need to seal the top and side flashings (but not the bottom) to your rain control layer with sheathing tape or peel and stick flashing. You could use backer rod and caulking around the perimeter of the window, but it is not necessary as your rain control layer and drainage gap will drain any water getting into these areas down the wall. It also important that water can exit and air (but not bugs) can enter the gap below the bottom of the siding. This can be accomplished using bug screen to cover the gap at the bottom.
Trevor
Trevor has given good advice. Look up Harvey for trim coil, they or their competition supply siders in your area and should have the color and someone to make the bends.
Harvey Building Products