warped sill


Old 09-09-12, 08:36 AM
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Join Date: May 2002
Location: kentucky
Posts: 129
warped sill

I am a rookie preparing to install replacement windows. In measuring the windows it is apparent that one of the windows has a warped sill causing almost a 3/16 - 1/4" gap at each jamb. I'm hoping it doesn't have to be ripped out. What typically is done.

Also when ordering windows, do you order the exact size of the opening or do you deduct a small value to allow for working space and if so how much.
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Old 09-09-12, 02:36 PM
XSleeper's Avatar
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Join Date: Dec 2004
Location: USA
Posts: 20,537
The problem that many people encounter is that replacement windows typically need a 1/4" deduction from the exact height and width of the opening. If you make the deduction, and then the person you are ordering the window from make the same deduction, you get windows that are 1/2" smaller than the opening, which creates some problems with the old trim covering the edges of the window.

So I guess the answer depends on the person ordering the window. If you make the 1/4" deduction, you need to make it VERY clear that you are giving them a "tip to tip" measurement, and that THAT is the exact size that you want those windows to be. I'm not sure how common it is anymore, but some companies used to deduct an inch from the height and then give you a "head expander" that you would install on top of the window. Questions on measurements really need to be talked about with the person ordering the windows so that you are on the same page.

But in short, I would recommend that you take exact measurements, and then make the 1/4" deduction and then ONLY give them the "tip to tip" measurements, and verify that is the exact size of the window you will get. Don't give them more than one measurement or you will be sure to confuse them.

As far as the warped (bowed) sill is concerned, it really depends how bad the warp is. If you can tell from the outside that the sill is warped, it should probably be replaced. If the sill is still solid, it could also be sanded/planed down so as to appear straight again, but that is usually more work than just replacing it. You can also chisel wood off the sill so that it is fairly straight, knowing that the replacement window is going to cover up the first 3 1/4" of the chiselled area.

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