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.
Ask TOH users about Windows

Contribute to This Story Below

    Tools List

    • circular saw
      Circular saw
    • detail sander
    • drill
    • hammer
    • flat prybar
      Pry bar

    Shopping List

    1. 8d stainless-steel ring-shank nails
    for casing

    2. 3½-inch deck screws for sill

    3. Two-part acrylic adhesive (The brand used here is Bond&Fill.)4. Cellular-PVC windowsill (The brand used here is Kleer Lumber, which has the most sill options. AZEK also makes a PVC sill.)