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Outside window sill damage is very common. Constant exposure to the elements can deteriorate wood in only a few years, causing it to rot or split. No matter how much paint you apply to it, it won't help. If your exterior sill is showing any signs of damage, don't be intimidated by what appears to be a built-in piece of wood. You can replace that ugly sill without disturbing the interior sash or woodworking with a few hand tools in about an hour.
Sills are decorative trims that fit under an existing window. Sills compliment the shape of a window and provide a more finished look. All sill tops are slanted slightly to allow for water to flow away from the building. Window Sills 85 inch stock lengths or Specified Lengths with Finished Ends.
1
Open the window. Tape plastic over the interior side of the window to prevent sawdust from entering the home. Measure the thickness of the sill. Set the blade of a circular saw to the measurement.
2
Place the circular saw in one corner. Tilt it up to 30 degrees and pull the trigger to turn it on. Slowly lower the saw until the blade cuts into the sill and the base of the saw is flat and flush on the sill. Push the saw forward, guiding it along the edge of the window sash. When the saw comes into contact with the other side, turn it off and pull it free.
3
Use a reciprocating saw to cut the remainder of the sill loose in both corners where the circular saw would not reach.
4
Cut across the sill in the middle perpendicular to the grain using the circular saw.
5
Insert a prybar under the sill from the front. Pry both pieces up and out one at a time. If the saw didn't cut all the way through the sill, pry harder to break it off and pull the sill free of the sash.
6
Clean the corners under the exterior trim where the sill fits under using a chisel. Cut off any remaining pieces of wood that broke off under the trim with the chisel. Use a hammer to pound the end of the chisel if needed to get the corners clean and square.
7
Clean any remaining debris or caulking from the area with a wire brush and a broom. Measure the distance between the sides of the window under the trim. Use a miter saw to cut the two-by-six fir to length. Measure the width of the sill. Use a table saw to cut the fir to width.
8
Pound the new sill into place under the trim with a hammer, protecting the sill by placing a wood block between the sill and the hammer blows. Caulk around the perimeter of the sill and underneath. Paint as needed.
Things You Will Need
- Masking tape
- Plastic sheeting
- Circular saw
- Reciprocating saw
- Prybar
- Chisel
- Hammer
- Fir lumber, two-by-six
- Caulk
Tips
- Some window sills have a sill nose. If your sill extends past the trim or the edges of the window on both sides, nail another piece of 1 1/4-inch fir to the exterior edge of the sill to match the old one.
- The sill thickness measurement is for a typical window sill; yours may differ.
Warning
- Wear safety glasses when working with wood.
About the Author
Specializing in hardwood furniture, trim carpentry, cabinets, home improvement and architectural millwork, Wade Shaddy has worked in homebuilding since 1972. Shaddy has also worked as a newspaper reporter and writer, and as a contributing writer for Bicycling Magazine. Shaddy began publishing in various magazines in 1992, and published a novel, “Dark Canyon,” in 2008.
Cite this Article Choose Citation Style
Shaddy, Wade. 'How to Replace an Outside Window Sill.' Home Guides | SF Gate, http://homeguides.sfgate.com/replace-outside-window-sill-49101.html. Accessed 19 June 2019.
Shaddy, Wade. (n.d.). How to Replace an Outside Window Sill. Home Guides | SF Gate. Retrieved from http://homeguides.sfgate.com/replace-outside-window-sill-49101.html
Shaddy, Wade. 'How to Replace an Outside Window Sill' accessed June 19, 2019. http://homeguides.sfgate.com/replace-outside-window-sill-49101.html
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