How to Install Replacement Windows

Score along the edge of the storm window frame with a utility knife and then remove the screws and use a pry bar or putty knife to remove the frame. A paint multi-tool (sometimes called a 5-in-1 tool) is also helpful for this step.

Older windows may have sash weights or sash springs that you need to remove.

• If your window has weights, cut the cords and let the weight fall inside the frame.
• If your window has sash springs, carefully remove them. Raise the sash near the top of the window. The springs might have plastic covers. If possible, cut and remove them. If you can't remove them, they'll break off when the springs are detached. Remove the screws holding the springs in place.

Identify any stops on the existing window. Old wooden windows have stops holding the sashes in place: interior stops, parting stops between the two sashes, and exterior stops. If you're installing from the inside, remove the interior stops and leave the exterior stops in place. If you're installing from the outside, as with this project, remove the exterior stops but leave the interior stops in place.

Use a utility knife to score where the stops meet the frame. You might be able to pry them off. If you can't pry the stops off cleanly, they're probably embedded within the frame and need to be cut using an oscillating saw. Let the saw blade do the work and be aware of nail locations. Remove the top sash and then remove the parting stop and the lower sash.

Apply flashing tape to the sill. It should fit the length of the sill and extend up the vertical leg of the stool (the bottom ledge of the interior side of the window). Be sure to work it into the corner of the stool.

Check the sill for level and make sure there's no bowing. If necessary, use shims to make the sill level. Ensure they're placed correctly for proper leveling and secure them with screws and flashing tape to prevent any movement.

Dry-fit the new window into the opening. You should have a small gap around the frame. Set the window aside.

Apply a 3/8-inch bead of silicone caulk at the interior head (the top of the frame), the stops and the sill. See How to Caulk to learn to lay a bead of caulk.

Place the window in the opening, resting it against the interior stops and pressing it firmly against the caulk. Use shims to secure the window, placing them at the pre-drilled frame screw holes. From the inside, drive screws into the holes and through the shims.

Check that the sashes sit evenly in the frame. If needed, use additional shims at the meeting rails (the horizontal frame elements on the sashes that meet when the window is closed) to adjust the frame of the new window.

Check for plumb (straight up and down), level and square, and ensure the window operates properly. You can make any necessary adjustments with shims. When everything is right, cut any shims that are still sticking out.

Measure the height from the bottom of the window to the sill to size the sill adapter.

Use a sharp utility knife to cut the sill adapter to the appropriate width.

Install exterior trim around the window frame with finish nails, and use a nail set to finish driving the nails to prevent denting the trim. Seal the edges of the trim with latex caulk, making sure to avoid covering the weep holes. Fill any noticeable nail holes with wood putty and paint the trim as needed.

Apply latex caulk along the interior trim to complete the installation.