Andersen windows, like other popular window makers today, manufacture replacement windows that are pre-hung and fully functional when they arrive. They’re already mounted in their casing, so you just have to install the casing into the opening as one single unit, instead of piecing together sashes and installing hardware as in the old days. Andersen makes several lines, including "insert" windows, which let you keep the existing frame and trim and replace just the window unit itself.
Things You'll Need
- Tape measure
- Andersen replacement window unit
- Batt insulation (paper-backed fiberglass)
- Utility knife
- Wood shims
- Screw gun
- 3-inch screws
- Trim nails
Pry off the thin strips of wood trim that sit in front of the existing window sashes using your hammer and flatbar. Make sure not to break the trim, as you’ll need to re-use it. Pull the sashes out of the opening.
Cut a strip of batt insulation to the size of the window sill, using your utility knife. Lay the strip on the sill, paper-side down. Lift your Andersen window onto the sill, so the bottom of the unit is standing on the insulation.
Push the top of the unit back into the opening, tucking additional insulation at the sides. Let the unit rest against the thin wood trim that borders the outer side of the opening.
Get the unit level and plumb (straight up and down), shimming under it and to the sides and using a level at various points to check it. When it’s right, secure it by driving 3-inch screws in through the sides of the unit to the surrounding frame, using your screw gun. Put one screw per screw hole. (There will usually be four to six screw holes, depending on the model.)
Use trim nails and your hammer to re-install the thin strip of trim that you took off earlier. The trim should "trap" the Andersen window unit in place. Caulk everywhere the unit meets the trim.
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