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Home Improvement > Doors & Windows > How to Retrofit a Window

Learn how to retrofit a window when the window is the wrong size for the opening.

Homeowners have elected to replace their current windows with upgraded double-hung windows that are a slightly different size from the current ones. As a result, they will need to remove the window frames and some wooden siding to retrofit the window openings, resizing them before installing the new smaller windows.

Step by Step Instructions with Video

Step
1

Plan the Project and Assemble Tools and Materials

Plan your project, purchasing the windows and other materials and then assembling your tools. The project requires power tools, so be sure the wear safety goggles to protect your eyes.

Step
2

Remove Trim from the Existing Window

Remove the existing trim from the old window, inserting a pry bar under the trim and tapping gentle with a hammer to pry it away from the house. This trim is made of simple one-by-fours that have lapped rather than mitered corners. We plan to reuse the trim and are careful to avoid damaging it.

Step
3

Remove the Sliding Glass Panels

Remove the sliding glass windows from the inside of the house. Remove them from the premises and dispose of them properly. Depending on their condition, you may be able to give them to a charitable institution or sell them for salvage.

Step
4

Mark a Cutting Line with a Compass and Pencil

Use a compass and pencil to mark a cutting line 2 inches around the widow to release the window flange (or fin). This metal strip is about 1 1/2-inches wide, runs around the perimeter of the window and is nailed into the framing of the house. You must cut away some of the exterior siding that covers it in order to remove it.

Step
5

Cut the Siding with a 3 1/2-Inch Circular Saw

Cut along the line with a 3 1/2-inch circular saw, holding the guard back and resting the front of the saw???s foot against the siding. You will need to adjust the depth of the exposed saw blade so that it will cut entirely through the siding, but not into the framing below.

Step
6

Remove the Strips of Siding

Remove the strips of siding freed by the cut, popping them out of position with a small curved pry bar.

Step
7

Remove the Nails from the Window Flanges

Remove the nails from the flange using a nail puller and a hammer.

Step
8

Remove the Old Window

Remove the entire window.

Step
9

Pry Out the Two-by-four

Pry up the two-by-four that the old window rested on at its base.

Step
10

Unpackage the New Window and Carry It to the Site

Remove the new double-hung and double-glazed window from its packing and carry it to the window site.

Step
11

Measure the Exact Dimensions of the Window

Measure the new window to determine how much you need to adjust the window opening. The window in this project is 45-inches wide by 47-inches tall. The window opening is both too wide and too short.

Step
12

Remove the Wallboard to Widen the Opening

Provide extra height in the opening by breaking out the wallboard that lines the interior perimeter of the window. Use a pry bar to reveal the corner bead, a metal strip that reinforces the corner. You will need to remove it without damaging the interior wall.

Step
13

Tap the Corner Bead to Crack the Wallboard

Tap against the corner bead carefully with the pry bar to produce a slight crack around the corner bead on the interior wall.

Step
14

Deepen the Crack with a utility Knife

Deepen the crack with a utility knife and cut the edge of the wallboard to prevent tears in the paper surface.

Step
15

Tap the Corner Bead to Push Out the Nail Heads

Tap again with the pry bar from the outside of the window to push out the nail heads that secure the corner bead.

Step
16

Remove the Nails

Extract the nails with the nail-puller and hammer. Remove the corner bead.

Step
17

Fill in the Extra Width of the Opening

Fill in the extra width of the opening with layers of exterior lumber on each side.

Step
18

Secure the Filler

Secure the strips with a nail gun.

Step
19

Lay the Window Face Down on a Work Surface

Lay the new window with its exterior face downward on your work surface. Two-by-fours spanning the space between two sawhorses will make an adequate worktable.

Step
20

Bend the Flanges Outward at Right Angles

Locate the nailing flanges and bend them outward at right angles to the window.

Step
21

Run a Bead of Caulking on Each Flange

Run a bead of exterior caulking down the center of each flange as the first of several moisture and air seals.

Step
22

Set the Window in Place

Set the bottom of the window in place and tip the window upward until the flanges are in contact with the frame/opening.

Step
23

Use a Bar Level to Ensure the Window Is Level

Have a helper hold the window in place while you confirm from the interior of the house that the window is centered in the opening. Use a bar level to ensure that the window is level.

Step
24

Insert Shims As Necessary

Insert shims as necessary to space the window and confirm that it is level.

Step
25

Secure the Window to the House

Hammer rust-resistant galvanized roofing nails into the flange and through the framing to secure the window to the house.

Step
26

Use a Nail Set Where the Hammerhead Will Not Fit

Use a nail set/nail punch to drive the nails in places where the hammerhead will not fit.

Step
27

Cover the Corner Gaps with Rubber Seals

Cover the gaps at the corners that were not lapped by the window flanges. Use self-adhesive rubber corner seals.

Step
28

Insert Strips of Roofing Paper

Insert strips of roofing paper along the entire perimeter as an additional barrier against air and moisture and tuck the edges behind the siding using a putty knife.

Step
29

Apply Exterior Caulking

Apply a bead of exterior caulking to fill the gap where the roofing paper meets the siding. This area has a significant potential for leaks, so be thorough.

Step
30

Fill the Gaps with Exterior Lumber Strips

Fill the remaining gaps around the window with narrow strips of exterior lumber to bring the surface flush with the exterior wall of the house.

Step
31

Secure th Strips with a Nail Gun

Secure the strips with a nail gun.

Step
32

Replace the Original Exterior Trim

Replace the trim that you initial removed from the window at the beginning of the project. Align the ends.

Step
33

Drive in Rust-Resistant Nails

Drive in rust-resistant finish nails with a nail gun to secure the trim.

Step
34

Add a Final Bead of Caulking

Add a final bead of caulk around the trim, sealing the gap between it and the siding.

Step
35

Smooth the Bead and Force It Into the Siding Grooves

Smooth out the bead with your finger, forcing the caulk into the grooves of the siding.

Step
36

Add Jamb Extensions

Add jamb extensions, from the interior of the house, to extend the jamb so that it fills the gap flush with the wall.

Step
37

Secure the Jamb Extensions with a Pneumatic Pin Nailer

Attach the jamb extensions with a pneumatic pin nailer.

Step
38

Nail Up the Interior Molding

Nail up the interior molding with the pneumatic pin nailer and the final step to complete retrofitting the window.