Step-by-Step Guide to Replacing a Window Sill

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Home renovation

A windowsill is the flat surface at the bottom of a window. It is exposed to all kinds of weather conditions, which is why it may need to be replaced. If your window sill is rotting or you just want to give it a new look, you can replace it in a few hours. Follow these steps to replace a window sill.


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


  1. Remove the inner window from the frame, from inside your home.
  2. Gently remove the old window sill from outside using the pry bar. Try to keep it intact to take measurements for the replacement. You can take the piece of wood to the hardware store and discuss wood options with a sales associate. Pretreated lumber will withstand the elements longer than untreated wood.
  3. Measure the rotting sill and trace the dimensions onto the new 2-by-6 piece of wood. Ensure accuracy by checking the measurements against the window.
  4. Cut the new piece of wood to fit the window sill using a table saw.
  5. Slide the new window sill into place and secure it by nailing galvanized screws through the outer edge of the sill and into the frame [source: Reader’s Digest].
  6. Fill in any gaps or leaks with caulking. Make sure 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 again [source: Silva].


1. What is a window sill?

A window sill is the horizontal surface at the bottom of a window frame that protrudes outside of the house. It is usually made of wood, stone, or concrete and is designed to prevent rainwater from entering the house and to provide a platform for placing items such as plants or decorative ornaments.

2. Why do I need to replace my window sill?

You may need to replace your window sill if it is damaged, rotten, or has become too worn out to function properly. A damaged window sill can allow water to seep into your house, which can cause mold and mildew to grow. It can also compromise the structural integrity of your window, making it less secure and less energy-efficient.

3. What tools do I need to replace a window sill?

You will need a pry bar, a hammer, a saw, a drill, a chisel, a measuring tape, a level, and a caulking gun. You may also need a reciprocating saw if your window sill is difficult to remove.

4. How do I remove the old window sill?

First, remove the trim around the window sill using a pry bar. Then, use a reciprocating saw or a chisel to cut away any caulking or adhesive that is holding the window sill in place. Finally, use a pry bar and a hammer to gently pry the old window sill away from the window frame.

5. How do I measure the new window sill?

Measure the length and width of the old window sill and add 1/2 inch to each measurement. This will ensure that the new window sill fits snugly into the window frame. Use a level to make sure that the new window sill is level before installing it.

6. How do I install the new window sill?

Apply a bead of caulk along the bottom of the window frame where the new window sill will be installed. Then, place the new window sill on top of the caulk and press it down firmly. Use screws to secure the new window sill to the window frame, making sure to countersink the screws so that they do not protrude above the surface of the window sill.

7. How do I finish the new window sill?

Fill any gaps between the window sill and the window frame with caulk. Then, sand the window sill and apply a coat of primer to protect it from moisture. Once the primer has dried, apply a coat of paint or stain to match the rest of the window frame.

8. Can I replace my window sill myself?

While it is possible to replace a window sill yourself, it can be a difficult and time-consuming process. If you are not comfortable working with power tools or have never done a home repair project before, it may be best to hire a professional to replace your window sill.

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