A. General Information
Problems with windows range from sticking sashes that need you to clean the tracks, to badly rotted frames that require you to replace the whole window. Annually inspect your windows and make repairs right away to keep small problems from becoming expensive problems.
B. When you have a sticking window
When you have a sticking window, the most common reason is because the channels or guides need cleaning, or because they've been painted shut. To loosen a sticky window, start by using a paint zipper or utility knife to score the crack between the window stop and the window frame. Work slowly to avoid chipping the paint on the window stop and sash. Hold a wood block along the window sash and strike it lightly several times with a hammer. Move the block up and down the sashes, then try to slide the windows up and down.
If this technique doesn't work, then the window frame might be warped or swollen. One solution for that is to remove the window stops and reinstall them so there's a very small but noticeable gap between the stops and the window sashes.
C. To replace broken glass
To replace broken glass, you have to remove the glazing putty and glazier's points, then carefully remove the glass. Take the exact measurements of the opening to the hardware store or home center - the replacement glass should measure ¼" less in each direction than the actual opening. This will provide a 1/8" expansion gap in each edge. You can install single-glazed glass by yourself, but don't try to replace double- or triple-glazed glass panels: that is for a professional installer. Begin by removing the window from its jambs, if possible.
Then, soften old glazing with a heat gun, being careful not to scorch the wood. Scrape away the softened glazing with a putty knife. Remove the broken glass and metal glazier's points from the frame, then sand the wood to clean away old paint and putty.
Coat the bare wood with sealer, and let dry. Then, apply a thin layer of glazing compound into the frame recess. Set the new glass into place, pressing lightly to bed it in the glazing.
Press in new glazier's points every 10", using the tip of the putty knife. Apply glazing compound. Some types of glazing are applied with a caulk gun and others with a putty knife. Smooth the glazing with a wet finger or cloth. After glazing sets, paint it. Overlap the paint onto the glass by 1/16" to improve its seal against the weather. Reinstall the window.
D. Too deteriorated to repair, replace it
If you have a window that is too deteriorated to repair, you can replace it. Buy a replacement window that matches the rough opening of the window, and wait for a dry day to do the job.
Begin by prying off the window aprons, stools, and casings, using a flat pry bar. If you plan to reuse them, save them; some new windows come with their own moldings. For double-hung windows with sash weights, remove the weights by cutting the cords and pulling the weights from the pockets. Cut through the nails holding the window and door frames to the framing members, using a reciprocating saw.
From the outside, pull the window from the opening. Make arrangements for help if the window unit is large. Applying masking tape across the panes of glass may prevent the glass from shattering if there is a mishap while you're removing the window.
Test-fit the new window, entering it in the rough opening. Support the window with wood blocks and shims placed under the bottom jamb. Check the window to make sure it's level and plumb. If needed, adjust the shims under the low corner of the window, until it's level.
Place pairs of wedge shims together to form flat shims. From inside, insert shims into the gaps between the jambs and framing members, spaced every 12 inches. Adjust the shims so they are snug, but not so tight that they cause the jambs to bow. Open and close the window to make sure it works right. Check again to make sure the window is still level and plumb, adjusting it if needed. At every shim location, drill a pilot hole, then drive an 8d casing nail through the jamb and shims and into the framing member. Drive the nail heads below the surface with a nail set.
Fill the gaps between the window jambs and the framing members with loosely packed fiberglass insulation to reduce air infiltration. Trim off the shims flush with the framing members, using a handsaw. From outside, drill pilot holes, then drive 10d galvanized casing nails, spaced every 12", through the brick moldings and into the framing members. Recess the nail heads, using a nail set. Apply silicone caulk around the entire window unit. Fill all nail holes with caulk, then paint the wood trim. Replace the interior moldings.
E. Loose joints on storm windows
If you have a removable wood storm window, loose joints are one of the most common problems you may come across. Remove the glass pane or screen insert and inspect it. If the pane or insert is damaged, clean and prepare the recess, and plan to replace the glass or screen after repairing the joint. Carefully separate the loose joint, using a flat pry bar, if needed. Use a putty knife to scrape the surfaces of the joint clean.
Use a disposable glue syringe to inject epoxy glue into the joint. Press the joint back together and clamp it into position with a bar clamp. Use a carpenter's square to check the frame for square. After the glue is dry, reinforce the repair by drilling two 3/16" - diameter holes through the joint. Cut two 3/16" - diameter dowels about 1" longer than the thickness of the frame. Round over one end of each dowel with sandpaper. Coat the dowels with epoxy glue and drive them through the holes. After the glue is dry, trim the ends of the dowels with a backsaw, and sand them until they're flush with the sash. Touch up the area with a coat of paint.
F. Replace the screen in a storm window
To replace the screen in a wood storm window, start by cleaning any old screening or retaining strips from the recess. Use an old chisel to scrape the residue from the recess, then apply a coat of primer or sealer to the window frame. Cut a piece of fiberglass screening at least 3" wider and longer than the opening in the frame. Use a staple gun to tack the top edge of the screening into the recess. Stretch the screen tightly toward the bottom of the frame, and tack the bottom of the screen into the recess. Then, tack one side into the recess. Stretch the screen tightly across the frame, and tack the other side into place. Attach retaining strips over the edges of the screen. Don't use the old nail holes; drill 1/32" diameter pilot holes into the retaining strips, then drive wire brads into the holes. Trim the excess screening with a sharp utility knife.
