How to Install Replacement Metal Window Frames

Slide a pry bar between the exterior window trim and the house. Use the pry bar to pull the trim from around the window. Go inside and slide the pry bar between the interior window trim and the wall. Pull the trim off the wall. If you plan to reuse either trim, work slowly to avoid damaging it.

Remove the vinyl siding surrounding the window. Slide a zip tool underneath the siding strip and pull down to free the siding. Move the zip tool down the length of the siding strip and lift it. Position a flat bar over the nail heads holding the siding strip in place. Hammer the flat bar behind the nail head and use it to pry the nail out. After you remove all the nails, remove the siding from the wall. Skip this step if you have a brick or stone house.

Cut the building wrap up from the opening's top two corners, using a utility knife. Make the cut at an outward 45 degree angle. Lift the cut portion and secure it in place with masking tape. If you have a brick or stone house, it will not have building wrap. Instead, paint a liquid flashing on the rough opening with a paintbrush.

Hold the aluminum window frame so the interior side faces you. Measure the distance from the nailing fin to the interior side's surface and add 1/8 inch. Transfer this measurement to the rough opening's bottom window sill. Use a flat edge to draw a straight line across the window sill at this measurement.

Measure the sill's length and add 6 inches. Transfer this measurement to a drain mat and cut it, using scissors. Measure 3 inches in from each end and place a mark. Line up the drain mat's back edge with the line you drew in Step 2. Lay the drain mat on the sill. Bend the mat up at the marks you made so it extends 3 inches up the rough opening's sides.

Peel off the drain mat's paper backing and push it into place. Staple the drain mat to the rough opening. Fold the drain mat down and staple it to the wall. Bend its sides to form corners around the rough opening's sill and staple them in place.

Place a tube of sealant in a caulk gun and cut off the tip with a utility knife. Run a bead of sealant around the nail fin's interior side, where it will touch the rough opening. Place the window's bottom edge onto the drain mat and tilt it up into the rough opening.

Hammer a roofing nail through the nailing fin's bottom right corner to help hold the aluminum window in place. Insert wood shims between the window's and rough opening's sides. Keep the shims at least 4 inches from each corner and about 8 inches apart.

Hold a level against the aluminum window and adjust the shims as necessary so it rests square in the rough opening. Hammer roofing nails through the nailing fin's holes to secure the window in place. Do not drive nails through the shims. Pull the shims out.

Apply strips of 6-inch-wide adhesive flashing around all four sides of the aluminum frame window. Overlap the flashing's ends at both the top and bottom corners. Roll over the flashing with a J-roller to remove all the wrinkles.

Lower the taped-up portion of building wrap and place it over the window's top nail flange. Tape down the cut sides with building wrap tape. Place the exterior window trim you removed in Step 1 around the window. Secure it in place with nails, if you have a vinyl siding house, or masonry screws, if you have a brick or stone house.

Go inside and spray expanding foam in the gap between the rough opening and the aluminum-framed window. Place the interior window trim you removed in Step 1 along the window's top, bottom and sides. Secure it in place with a pneumatic nail gun and finishing nails.