Years of exposure to the elements will eventually rot wooden window sills. You need to know how to replace a window sill to prevent the damage from spreading farther into your home’s structure. You can expect this project to take about half a day.
How to Replace a Window Sill Steps
- Cut through the caulk around the window frame and trim with a utility knife.
- Carefully lift away trim pieces with a pry bar. Take care not to break the pieces because you can reuse them.
- Have a partner hold the window.
- Using the reciprocating saw with a fine tooth blade carefully cut around the window. The blade will sever the nails holding the window in place.
- Take out the window and the bottom framing member.
- Cut a central section out of the old sill with the reciprocating saw.
- Pry out remaining pieces of sill and make sure to pull or pry out any remaining nails.
- Driving a screw into the old sill to give the pry bar something to grab can be helpful.
- Measure the old framing member and cut a new one from a cedar 2 x 4.
- Secure it into place with 16-gauge 2-1/2-inch nails.
- Measure the old sill and cut a new one with notched corners from 2 x 6 cedar board.
- Replace or add some insulation into the cavity beneath sill.
- Use a table saw to make 1/4-inch deep kerf cut into the bottom of the sill parallel with its outer edge.
- Fit new sill into place and nail it.
- Add wood filler to any holes and cracks in wood around the window.
- Cover exposed wood around the window with insulation paper.
- Re-install the window and put the trim back on.