Replace window sills under vinyl windows?


Well-Known Member
So my house is about 30 years old and has dual pained vinyl windows that have for the most part held up well. I have two windows that are in perpetual shade and it appears the sill is rotting out from under the window, though it's hard to tell because there's only a small amount of exposed wood on the front sides where the vinyl frame wraps around the sill. When I bought the house the inspector told me to keep up on painting the exposed wood on these windows, but they appeared to be too far gone.

Last year or the year before I dug out all the soft wood and plugged them up with caulk. This year I noticed it separating and behind the caulk a bunch more wood had rotted (and was still wet even though it hasn't rained in a week).

So now I have a few questions, how the heck can water be getting to this wood? It's basically completely encapsulated except for weep holes in the vinyl window and siding, which itself shouldn't really get wet much because they are protected from the rain. could it just be exposed shaded wood combined with our near 100% humidity (but this wouldn't explain continued issue after caulking)?

More importantly, can the sill be replaced without replacing the window? I have done a LOT of diy in my life, but never put in vinyl windows. I think they are all one piece, could possibly be removed in one piece while the sill is replaced and then put back? How do I keep this from happening again? Does it even need to be replaced? The window isn't falling out, and if were a major water infiltration issue I should see other signs like water migrating into the house, right?


Just sneakin' around....
If the window is vinyl and the sill wood, chances are the window was a replacement and used the old wood sill. Without looking at it, I'd say the sill could be removed separately.