Replace Rotted Windowsill

Tools:

workbench
sawhorses
table saw with a fence and miter gauge
carpenter’s pencil
push stick
carpenter’s square
power drill
rag
reciprocating saw
hammer
folding rule
bricks
caulk gun
5 in 1 tool
cat’s paw
circular saw
safety glasses
dust mask
pretreated lumbar
2x6
1x6
screws
nails
caulk

1. Raise the sash and remove the top plate. Pry away as much material as you can. Use the reciprocating saw to cut through solid material and clear it away (figure A).

2. Next pry out the main part of the sill. Try to keep it as a whole piece so you can use it as a template to cut a replacement (figure B).

3. Use the folding rule to get inside measurements to cut a new top plate (figure C).

4. Place the old sill on a 2x6 and trace around the edge to mark cut lines (figure D). While you're at it, mark the measurements for the top plate on a 1x6.

5. Cut the new pieces using a table saw. Be sure to wear a dust mask and safety glasses when working with power tools.

6. Slide new sill into place, then pry away interior trim to slide the top plate into position. Drive galvanized screws down through both pieces and into studs below. Secure the bottom sill by driving screws through the outside edge.

7. Run a bead of caulk along the edge to seal any gaps (figure E). Reattach trim pieces if necessary.