The do it yourself resource for homeowners from home improvement professionals.

How to Replace a Windowsill

The elements continually batter windowsills in the Delaware Valley. Eventually, the rain, snow, ice, and temperature extremes take their toll and will result in your windowsills needing to be replaced. Skilled DIYers have the ability to follow the process of how to replace a windowsill. The greatest challenges are wrangling the old sill out and cutting the new sill to the necessary size.

How to Replace a Windowsill Directions

  1. Cut caulk around windowsill with utility knife.
  2. Slide the blade of an oscillating saw beneath sill to cut through nails.
  3. Using a reciprocating saw, cut middle section of sill at both ends near window jambs.
  4. Pry out middle section.
    1. Driving a screw into the front face of the middle section with a power drill will give the pry bar something to grab.
  5. Remove ends of the windowsill, or horns, with the pry bar and chisel.
    1. Use the oscillating saw if necessary, to cut nails holding the horns.
  6. Clean any debris out of space formerly occupied by windowsill.
  7. Scrape off old caulk with chisel or putty knife.
  8. Pull out any nails that might be left or cut them flush with the window stool with the reciprocating saw.
  9. Measure depth for new windowsill.
  10. Measure width between window jambs.
  11. Measure total length of windowsill from edge to edge.
  12. Transfer measurements to new board.
  13. Cut board with circular saw or handsaw to proper length and width, leaving notches to form new windowsill horns.
  14. Cut a shallow drip groove on the underside length of windowsill’s outer edge.
  15. Sand the surface of the new board.
  16. Apply caulk to edges of space receiving new windowsill.
  17. Apply insulating foam to back of windowsill space.
  18. Insert new windowsill and push firmly into place.
  19. Nail windowsill to window stool.
  20. Caulk between windowsill and stool.

Tools & Materials

  • Oscillating saw
  • Reciprocating saw
  • Circular saw
  • Handsaw
  • Pry bar
  • Chisel
  • Power drill
  • Measuring tape
  • Caulking gun
  • Hammer or nail gun
  • Sanding block
  • Carpenter's pencil

Professional Window Replacement Available

If you have many windowsills to replace, the project might eat up days of your time. You can save time and enjoy quality results by calling PJ Fitzpatrick. We have a large selection of replacement windows available. For help with any of your window repairs, ask us for an estimate today.

Need help with this project?

We have trained professionals that can help. Contact us today. 1-877-246-4354

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