How To Replace an Exterior Window Sill

Window sills need to be replaced eventually because they’ll be damaged, which might result to different problems. Below are steps and guides to help you replace an exterior window sill.

  • Materials you need. You need a caulking and caulk gun, flat pry bar, nail set, hand gloves, plain medium sandpaper, pair of locking vise grips, wood stock (Douglas Fir, pine, or redwood), primer-sealer, paint brush, galvanized casing nails (#16 or #12), framing hammer (20-ounce straight claw), reciprocating saw, saw horses, and circular saw.
  • Cut the window sill in two pieces. It will make the removing process easier. First, you need to adjust your circular saw. The saw blade’s thickness and depth must be similar with the sill. The cut must start at the sill’s outward edge. Then, head the cut for the window. Cut as much as the space allows. Turn off the saw and remove it afterwards. You need another instrument to end the cut. You can use a wood chisel, handsaw or reciprocating saw to finish the cut. Select a tool that suits your handyman skill.  
  • Pull the half part of the window sill first before pulling the other part.  Utilize your pry bar. Wear heavy duty gloves if it’s hard for you to free each board piece. Work gradually to free every board piece. Set the sills aside in a safe place.
  • Pull the nails out. Use your vice grips to execute this. Set the vise grips’ jaws so they will hardly bite into each nail. Then, close the vise grips’ jaws around each nail. Now, loosen each nail gradually. There are times that you need to use the locking pliers’ nose for leverage.
  • Identify the precise dimension of your new sill. Gauge and compare it from the two old sill pieces that you’ve removed. Figure the saw blade’s thickness and overall length.
  • Cut another sill from your softwood stock.  Don’t build-up a wood to make a new sill. Instead, use another wood stock piece if possible. Use redwood, cedar or cypress if moisture starts to give you difficulty.
  • Make the exterior edge rounded. Use a plane to achieve the effect.
  • Polish the board. Sand the board, and then use a primer to paint each edge and side.
  • Slither your new sill into position. Tightly nail it by using galvanized casing nails. Position every nail a little beneath the surface. Fill it with caulking. You must also apply caulk around the new sill’s edges.
  • Paint your new sill. Use high quality finish exterior paint.
  • Tips in replacing an exterior window sill. If the old sill’s rotten, you might not need to cut it to remove it. Water damage is a major concern in window exterior sill but it isn’t an enough reason to replace it.

Find rotting areas or water damaged spots beyond an exterior sill. It can be a building’s wooden frame. Replace a damaged sill immediately so the concern will not intensify. Ask for help or hire an expert to do the task for you if you doubt your skills or if you have a hectic schedule.


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