How to Repair a Rotted Windowsill
A quick guide to fixing exterior window trim without replacing the window
Q: One of our windowsills appears to be rotting. Can it be replaced without buying a new window?
—Bill Bailey, Baldwin, Mo.
David Raymond, Raymond Design Builders, replies: Sticking out into the weather year after year, wood windowsills take quite a beating. They can last for decades if you just keep them clean and protect them with a coat of paint. But when water gets trapped in or against them, as happens with improperly flashed windows, rot can take hold.
A simple epoxy repair will do the trick if the rot is confined to a small area, but if more than 10 percent of the sill is rotten, the old sill should be cut off and replaced. For this project, I used a solid piece of Kleer cellular PVC sill that matches the profile and thickness of the other sills on the house. It costs less than a piece of clear, milled red cedar and is paintable, but no matter how many times it gets wet, it can't rot.