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Two windows with blinds closed and grey curtains on either side.

How To Replace Interior Window Sill

Repairing or replacing old window sills is an easy home repair project that only takes a few hours and basic tools.
Keyword replacing window sill, window sill repair
Cook Time 2 hours
Total Time 2 hours
Servings 1 window
Author Rachel
Cost $30



  • Cut the caulk line around both sides of the casing and the window sill itself. Drag a razor knife top to bottom to do this, making sure to get the full caulk line if you can.
    Razor knife cutting caulk around door casing.
  • Use a crowbar to pull out the casing from the drywall. If prying, make sure to use a brace against the wall so you don't dent the drywall.
    Crowbar removing door casing.
  • Use a prybar or chisel to slowly pry the sill up. A hammer also helps. Try to keep the sill in one piece so you can use it as a model when cutting the new sill.
  • Measure the sill area and use the old sill as a template if possible. Cut the new sill to size. Dry fit several times as the walls is likely not be completely straight.
  • Use nails or brad nails to install the wood board into place ensuring that it is nailed into the framing below.
  • Reattach or replace the side casing and trim that was removed with nails or brad nails.
  • Complete the finishing of the window. Fill and smooth all nail holes with wood filler and patch walls if necessary. Caulk around the edges of all the window trim and frame. Prime and paint as needed to match the existing trim in the house.
    Two windows with blinds closed and grey curtains on either side.


General Tips
  • I have used a lot of wood filler and this is my favorite product. I thinned it out with a bit of water to get in the smaller areas.
  • For filling this type of wood, I love these sponges because they have edges that I can easily control and get into the ridges.
  • Try to find real wood products rather than the cardboard-like pressboard that new houses use. It is a much better product that is less prone to damage and problems.
  • If you would like more information on caulking, check out our step-by-step guide to Caulking baseboards.