wood window sill

Old 12-03-08, 02:07 PM
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Unhappy wood window sill

I need to know what would be the easiest way to replace the bottom sill that has rotted out on a wood sash window. It is surounded by brick. Would it be best to cut out the rotted part or remove the hole window, and replace the lower section.of the window frame itself. and if so what would be the best way to do it?
Old 12-03-08, 03:39 PM
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The nature of your question makes me suggest you should consult a professional. There is no really easy way to replace a rotted sill, and how much is rotted may determine the procedure. Tearing out the window should only be followed by installing a new window. If the rot is not widespread, an epoxy wood filler may work once the rot is removed. The worse the rot, the more work is needed, but there is no written way to deal with the problem.
Old 12-03-08, 06:31 PM
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Consulting a professional is a good idea, and I assume JustBill means having someone actually look at it, in person. Unfortunately you probably aren't going to find too many contractors who would be willing to come out and replace one window sill, however. It's pretty labor intensive, which means it's hard to charge enough for such a small job. Maybe a handyman would tackle it. The wood filler (or Bondo) that JustBill mentioned would work for a few years if you want a temporary fix.

If you KNOW the sill needs to be replaced and you'd like to attempt this yourself, it's not terribly difficult, but you NEED to have 2 tools: a reciprocating saw and a table saw. If you don't have them, forget it. If you do, read on.

Typically, rotten sills can be completely cut out and replaced. In a few instances, just the nose of the sill can be replaced, without having to tear out the whole sill. (that's where a professional might be able to make the call if he saw it in person). If the entire sill will be replaced, you generally need to carefully cut the stool free from the sill by slipping a reciprocating saw w/metal blade between the stool and sill (open the window and do this from the outside) in order to cut the nails holding the stool. Once they are cut, the next thing to do is to make two cuts through the sill, so as to remove a chunk out of the middle of the sill. I typically leave about 2" of sill on the left and right sides of the jamb. Once you've made the 2 cuts, and have cut completely through the sill, you can lift that chunk up and wiggle it out. The portion remaining on the left and right sides can be split into pieces by whacking them on the cut ends with a chisel. Try not to damage the bottom ends of the jamb as you do this. Cut, nip or grind off the nails that are left in the jamb.

Your new sill needs to be exactly as thick as the old one was. It also should be at least as wide as the old sill was, if not a little wider. Usually you can use the chunk you cut out as a sample. You'll cut an angle on the front and back of the new sill so that when you look at the new sill from the side, it will be shaped like a parallelogram. Then you make two cutouts on the left and right sides of the sill so that it will fit around the jamb as you slide it in. This takes some careful measuring. Typically, you measure the length of the sill, and cut your piece to the right length Let's say it's 36". Then measure the distance between the legs of the jamb. Let's say it's 31". You would need to notch 2 1/2" off of each side, if everything is perfectly centered. Now you want to know how deep the notch will be. Measure the length of the slope of the jamb, from the surface of the sheathing, back to the point at which the sill stops and your trim begins. Usually it's about 4 5/8" or so. So you'd draw that square notch on each corner, and cut it out. Once you do that, your sill "should" fit. Don't make it too tight, though... or you'll never get it in. Or you'll get it 3/4 of the way in, and then won't be able to get it back out. LOL Don't ask me how I know that.

In some cases, you will want to cut a shim to set on the rough opening to hold the sill up. If the bottom ends of the window jamb are rotten, there won't be anything to hold the sill up at the proper angle. A short piece of 2x2 with the right angle on it, that is the right height works well. as you shove the sill into place, stuff some fiberglass under the new sill, or before you shove it all the way in, add a little low pressure door and window foam. Don't add too much or you will have a mess. Once it's in, renail the stool to the sill with some finish nails. You can also screw the sill up tight to the face trim from underneath if you so desire. You'd also put a few long finish nails or finish screws through the sill and into the framing below the sill. Caulk the bottom of the sill where it meets the siding.
Old 12-04-08, 08:41 AM
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Leslie - A few years ago I purchased an older cottage as a vacation place. Every sill in the house (17) was rotted or split and leaking.

I replaced them all over a couple of weekends using almost exactly the same methods outlined by XSleeper. I don't have anything to add to his procedure I just wanted to assure you that this is definitely a DIY job if you are at all handy.

I removed a bad sill and it was easy to duplicate the profile on a table saw. Even if you don't have a table saw, I'm sure you could get one made in a local shop. Replacing the first on took half a day. By the time I got to the last it was nearer half an hour.

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