How to Install Impact Windows in Wood Frame Houses

Raise the bottom sash up to open the old window. Hold onto the sash's bottom edge and give it a quick tug out of the side jambs. Set the bottom sash aside. Lower the top sash a few inches. Hold onto the sash's top edge and tug it out of the side jambs. Set the top sash aside.

Insert a pry bar behind the interior molding secured around the window's perimeter. Use the pry bar to remove the molding. Go outside and repeat this step with any exterior molding. You might need to cut through some caulk with a utility knife before the exterior molding will come free.

Fit a reciprocating saw blade between the old window's frame and the rough opening. Cut through all the nails and screws holding the frame in place. Gently lift the frame out of the rough opening.

Lift the impact window into the rough opening and center it. Ask a friend to hold the window in place from the outside while you return inside. Set a level on the window's sill. Insert wood shims underneath any low areas to lift them up and level the impact window in the opening.

Set the level against one of the impact window's side jambs. Insert wood shims approximately 2 inches from the impact window's upper-left corner to fill the gap between the window and the rough opening and help hold the window plumb. Drive a 2-inch screw through the window's frame and into the rough opening using a drill and Phillips driving bit.

Open and close the impact window to make sure it works smoothly. Insert wood shims along the window's sides, approximately 4 to 6 inches apart. Drive a 2-inch screw through the window frame at each shim location to hold the window in the rough opening.

Score each wood shim where it extends past the rough opening with a utility knife. Bend the shims to break them off.

Place a tube of silicone caulk into a caulk gun and cut off the tip with a utility knife. Apply a bead of caulk around the window from the exterior side to fill any gaps between the impact window and rough opening.