Open the window and look at the sides. Find the thin strips that run vertically on each side and sit flush against the moving part of the window, which is called the lower sash. These strips are called stops. [3] X Expert Source Michael FoxWindow Repair Specialist Expert Interview. 1 December 2020. The stops sit in front of the stash on the interior side of the window. The jambs, or the window’s side posts, are past the stops and are in line with the sashes. Notice that the distance between the stops is shorter than the distance between the jambs. If you’d measured from the stops, your replacement window would be too small.
With the window open, look at the bottom of the frame. The sill is where the sash sits. Don’t confuse it with the stool, or the molding on the inside of the window that gives it a finished look. The stool is higher than the sill and, like the stops, would throw off your measurements. Sills are often sloped to divert water away from a home’s interior. If your window sill is sloped, take the measurement from its highest point. Additionally, use a protractor to measure the angle of the sill’s slope. Some replacement windows offer a choice of sill angles. [4] X Research source
If there’s a difference of less than 1⁄4 to 1⁄2 in (0. 64 to 1. 27 cm) between the diagonal measurements of your frame, you can make small adjustments with shims when you install the new windows. If the difference is any larger, consider contacting a professional.
You may need to purchase a custom window to fit your measurements. For the easiest and most energy-efficient option, go with vinyl replacement windows with their own self-contained jambs and sashes. [7] X Research source
Do your best to avoid damaging the stops, as you’ll reattach them once you’ve installed the new window. If you happen to crack a stop, take a bit of wood filler and mold it onto the damaged part. Let it dry for about 15 minutes, and sand down the filler and the surrounding wood. Then give it a new coat of paint before reattaching to the frame. If you accidentally snap a stop in half, either patch it together with wood filler or purchase a 1 1⁄2 by 1⁄4 in (3. 81 by 0. 64 cm) furring strip from the hardware store. This should be the matching size, but measure your stop to be sure. Saw the furring strip to match the height of the other stop.
If the lower sash doesn’t slip out and you don’t see cords, it might have metal jamb liners or springs. Look for nails or screws that secure spring boxes to the sash, and remove any you find. [10] X Research source
In a double-hung window, both the upper and lower sashes open and close. Leave the exterior stops on the window frame. These outside strips are the counterparts to the inside stops, or the strips that you pried off the frame on the interior side of the window. The exterior stops will help guide the replacement window during installation.
Wait at least 15 minutes for the filler to dry, sand it with 120-grit sandpaper, then paint it to disguise your work. Filler drying times may vary by brand and the depth of your repair, so check your product’s specific instructions. If your window has weight wells, or cavities on the right and left sides, fill them with fiberglass or foam insulation after removing the weights. [13] X Research source To cut down on clean up time, use a shop vac to remove peeled paint and other debris.
Instead of trying to install the new window or reinstalling the old one, your best bet is to screw a plywood board over the exterior side of the window until your contractor can inspect it. A replacement window needs to be installed in a solid, rot-free frame, and a rotted frame could be a sign of larger structural problems. [15] X Research source
A large window is heavy, so get help lifting it to avoid dropping it or injuring yourself. If you measured carefully, the new window should match the opening. If it’s too small, you can add furring strips to the jambs to match the new window. For instance, if there’a a 1 1⁄2 in (3. 8 cm) gap on either side of the new window, screw 1 in (2. 5 cm) furring strips to the side jambs, or the posts on the left and right sides of the frame. If the new window is too large for the frame, return the window, if possible. If you can’t exchange the unit, you’ll need to cut into the raw opening. This is best left to a professional.
The stool is the interior molding that sits on top of the sill to give the frame a finished look.
Secure the window by loosely driving a 2 in (5. 1 cm) screw through an upper side jamb. At this point, you just want to hold the window in place so you can check its function and, if necessary shim it. Most modern replacement windows have pre-drilled holes; drive the screw into one of the upper side jamb holes.
If it doesn’t open and close smoothly, check it with a bubble level. Add shims, or scraps of wood approximately 1⁄8 to 1⁄4 in (0. 32 to 0. 64 cm) thin, between the replacement window and the sill to prop up 1 side. Once it’s level, trim the lengths of the shims that stick out with a utility blade or handsaw.
The screws should be snug, but not over-tightened. Placing shims by each pre-drilled hole will help secure the window and keep the frame from bowing. Trim the parts of the shims that stick out with a utility blade or handsaw.
Repeat the steps to replace the inside stop on the other side of the frame. Depending on the design of your replacement window and condition of the existing frame, you may also need to use the same technique to hammer trim onto the exterior. Adding or replacing exterior trim can also give your windows a more polished look.
The jambs of the replacement window frame the sash, or the parts that open and close. The boundary between the existing frame and the outside of the replacement window is the gap you want to caulk. Otherwise, the window wouldn’t be able to open! Use foam-rubber backer rod to fill gaps larger than 1⁄4 in (0. 64 cm). Insert the rod into the gap, then apply beads of caulk over the rod to seal it.
