Step 11: Shim as Necessary

adjust the unit by inserting shims under the sill and behind the side jambs until it is centered in the space and opens, closes, and locks smoothly
Photo: Russell Kaye
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Adjust the unit by inserting shims under the sill and behind the side jambs until it is centered in the space and opens, closes, and locks smoothly. Measure the window diagonally from corner to corner; the measurements should be the same. When the window is square, screw it in place through the predrilled holes. To avoid bowing the frame, slip a shim behind the jamb at each screw, then screw through the shim. Trim the shims flush with a utility knife.
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    Tools List

    • 100-foot tape measure
      Tape measure
    • hammer
      Hammer
    • flat prybar
      Flat pry bar, used to remove old window stops and jamb liners
    • putty knife
      Putty knife, for applying wood putty
    • caulk gun
      Caulking gun with exterior-grade elastomeric caulk
    • drill
      Cordless drill/driver, used to drill holes and drive screws
    • spade bit
      3/8-inch spade bit, for boring foam-insulation access holes in window frame
    • paint scraper
      Paint scraper, used to scrape loose, blistered paint from window frame
    • utility knife
      Utility knife, used to trim shims flush

    Shopping List

    1. Insert replacement window
    sized slightly smaller than existing window frame

    2. Exterior-grade wood putty
    used to patch holes in window frame

    3. Minimally expanding polyurethane foam
    used to insulate wall around window

    4. Wood shims
    for adjusting the window to sit level and plumb in opening

    5. 100-grit sandpaper
    for smoothing window frame prior to priming and painting 6. 2-inch screws
    used to fasten replacement window to frame

    7. Foam-rubber backer rod
    used to fill 1/4-inch-or-wider gaps prior to caulking

    8. Interior window stops
    needed if the original stops broke during removal

    9. Paintbrush, primer and paint
    for applying fresh finish to window frame