Step 1: Remove the Side Casings

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.
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    Tools List

    • circular saw
      Circular saw
    • detail sander
    • drill
    • hammer
    • flat prybar
      Pry bar

    Shopping List

    1. 8d stainless-steel ring-shank nails
    for casing

    2. 3½-inch deck screws for sill

    3. Two-part acrylic adhesive (The brand used here is Bond&Fill.)4. Cellular-PVC windowsill (The brand used here is Kleer Lumber, which has the most sill options. AZEK also makes a PVC sill.)