How to Replace a Window Sill

A man painting the trim around a window inside his house.
Windowsill is the horizontal structure or surface at the bottom of a window. michellegibson / Getty Images

Window sills experience the worst of all the seasons -- from the heat of the summer to the rain and snow of the winter -- so it's no wonder that they are frequently replaced. If your window sill is rotting or if you just want to give your window a fresh look, you can replace the window sill in an afternoon. Read the steps listed below and learn about how you can replace a window sill.



  • Pry bar
  • Pencil
  • 2-by-6 piece of wood
  • Table Saw
  • Hammer
  • Galvanized screws
  • Caulking

Here's what to do:

  1. Remove the inner window from the window pane, from the inside of your home.
  2. Remove the window sill from the outside, using the pry bar. Be as gentle as possible to keep the sill intact, so you can measure it when cutting a replacement. You may want to take the piece of wood to the hardware store and discuss your wood options with a sales associate. Pretreated lumber will stand up to the elements longer than untreated wood.
  3. Trace the measurements of the rotting sill onto the fresh piece of 2-by-6. Ensure accuracy by making sure the measurements you take from the sill fit the window.
  4. Saw the fresh piece of 2-by-6 to fit the window sill, using the table saw.
  5. Slide the new window sill into place. Secure it by nailing galvanized nails through the outer edge of the sill and into the frame [source: Readers Digest].
  6. Fill in any gaps or leaks with caulking. It's important to do a thorough job of caulking. If water seeps into the wood, it will warp quickly and you will need to replace the sill frequently [source: Silva].