window sill installation

Old 06-16-08, 01:36 PM
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window sill installation

My windows have sheetrock returns and are only missing a window sill. I held a prefab stair tread up to the spot and it looked pretty good. I just don't know what thickness it needs to be (how much reveal of the window frame?). Also how much overhang should there be, how is it fastened to the 2x10 underneath , how deeply should it be notched on the sides, how do I trim it out underneath and do I need to hide the end grain on the sides where it sticks out of the opening (it will be painted)? I was hoping the stair treads would work, since they already have a rounded front.
Old 06-16-08, 09:40 PM
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Can't say what the thickness should be without seeing the window in question. Digital pictures can be uploaded to photobucket or a similar web site, then the link can be pasted here. If the stair tread looks good up against the window and isn't too tall, then you're good to go. With window stools, the thicker the better. I've seen thin stools warp when they got wet... such as when someone forgot to close the window during a rain.

The piece under the window stool is called the apron, and it can be anything you like. Usually a piece of casing placed thick end up/narrow end down works well, but it could be anything you like.

You usually want the nose of the stool to stick out past the wall by at least twice the thickness of the apron. So if you use a 3/4" thick 1x4 as your apron, you'd want the "ears" of the stool to protrude 1 1/2" past the wall surface.

You'd attach it to the framing below with finish nails, or finish screws. A few well placed brad nails into the apron (once it is installed) wouldn't hurt either.

On the sides, you could cut those "ears" at a 45 and cut a left and right return. Picture it like the front of the stool is turning a 90 degree corner. If the ears of the stool protrude 1 1/2" past the wall, your return pieces would be right triangles, 1 1/2" long, with the curved portion on the left and right sides of the stool as it returns to the wall.

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