How to Repair a Rotted Windowsill

The casing comes off to clear the way for removing the old sill. If the casings are rotting, as here, replace them, too. Slice through the caulk bead between the siding and the casing, then carefully pry off each piece. Save the trim to use as templates for the new ones. Make sure the flashing behind the casing is intact and properly installed behind the siding.