Replacing a Large Exterior Window Sill

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Forum topic by one60fourth posted 11-04-2017 06:13 PM 394 views 0 times favorited 4 replies Add to Favorites Watch
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34 posts in 2360 days

11-04-2017 06:13 PM

Topic tags/keywords: home repair

I have a large multi-pane window in my living room (5’ x 5’). It is a single framed window and does not move. The exterior sill (6”W x 5’L x 1 3/8” thick) needs to be replaced due to a large area of rotted wood. Am I correct in assuming that the only way to remove and replace the sill is to remove the window first? Is it likely that there is a way to expose the full sill from underneath and remove it that way? There is currently a decorative face board and some other trim under the sill preventing me from accessing it fully.

4 replies so far

View Loren's profile


10477 posts in 4416 days

#1 posted 11-04-2017 06:16 PM

You will find it much easier to replace the
rotted wood if you remove the window. If
you’re prepared and organized you may be
able to get the window out in the morning
and have it back in by the end of the day,
even without experience.

View WhyMe's profile


1280 posts in 2329 days

#2 posted 11-04-2017 06:32 PM

It is possible to remove and replace a window sill without removing the window. Depending on how the unit is constructed will determine the ease or difficulty of the job. I have done it and it can be a fiddly job and take a lot of experience and the right tools.

View one60fourth's profile


34 posts in 2360 days

#3 posted 11-04-2017 09:11 PM

Thanks Loren and WhyMe. Looks like the best way is to remove the window. I think I’ll have to go with the partially rotted sill for this winter though. Pretty cool now in New England to have a hole in the house a whole day. I could put up a sheet of ply I guess but doing it in summer would take the time pressure off. Only 2.5” x 18” of the sill is rotted (terribly so!) on the outside edge. I don’t think it will have any impact this winter. Thanks for your opinion.

View one60fourth's profile


34 posts in 2360 days

#4 posted 11-04-2017 09:38 PM

I have one more question that I think the two of you might know how to answer. I’ve been replacing old glazing in many of the crank-out multi-pane windows I have in my house. (I’m using Dap33 putty.) I know the general advice is to overlap the glass about 1/32” when applying the final coat of paint to the glazes. I guess this helps keep moisture from seeping into any gaps between the putty and the glass. Keeping those lines straight is a tricky thing though. Not sure I can do it. I foresee lots of razor blade clean-up after painting and a lot more time invested in this project.

So here’s my question: I learned today that there is a liquid film product that you can paint onto the entirety of each glass pane. This film peels off when you’re done painting leaving nice clean lines—but alas, no overlap onto the glass. Would avoiding the overlap in favor of liquid film be a huge mistake? I wonder how effective a 1/32” sliver of paint could protect the seam anyways.

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