Replacing windows is not really as difficult as you would think it is. It is not very important that you hire professional window installers when replacing an individual window. It will take just a little bit of hard work and time to do so with the help of some instructions and general household tools.
The most essential step in the window-replacement process happens long before the installation day. This is when you measure the dimensions of the old window frame to make sure you order replacement windows with accurate sizes.
Start by taking measurements from the inside width of the old window frame, jamb to jamb, in three places: across the top, middle, and bottom. Write down the smallest of the three measurements. Next, measures the frame’s height from the top of the sill to the underside of the head jamb in three places: at the left jamb, in the middle, and at the right.
Then record the smallest measurement. Also check the squareness of the frame by measuring the diagonals from corner to corner. If the frame is out of square by 1/4 inch or so, don’t worry; the replacement can be made to fit. Anything more may require adjustments to the frame. If the frame is so out of whack that a square replacement wouldn’t look right, you’ll need a full-frame replacement.
Furthermore, remove the old sash from the window frame. In most cases, you’ll need to force open or unscrew the interior wooden stops to remove the lower sash. Next, take out the parting beads to free the upper sash. Simply press in on the jamb liners and pull the top of the sash forward. Then pivot one side of the sash upward to free it from the jamb liners.
If the window frame was fitted with vinyl or aluminum jamb liners, use something like a flat bar to force open them free. But if it is an original window, remove all remaining wooden stops from the window frame. Leave the interior and exterior casings intact. Scrape off all loose and blistered paint and patch any holes or cracks with wood putty, then sand the jambs smooth, and then prime and paint the surfaces.
If the original sash weights are still in place, take this opportunity to remove them from their pockets and insulate behind the window frame. Unscrew the access panel on each side jamb and pull out the weights. You may use polyurethane foam because it’s more effective at blocking air than fiberglass insulation. Make sure to use only low-pressure, minimally expanding foam intended for windows and doors; anything else will bend the frames and keep the sash from working. First, pull out any existing fiberglass in the weight pockets.
Then bore 3/8-inch-diameter holes, one near each end and one in the center, down through the sill and up through the head jamb. Put the expanding foam into the holes until it begins to ooze out. Also spray foam into the sash-weight pockets in the side jambs. Allow the excess to harden up for some time, and then cut it off to flush before replacing the sash-weight pocket panels.
Before installing the window, apply an elastomeric caulk to the exposed inner face of the exterior casings or to the blind stops on the top and sides of the frame. Also apply two continuous beads of caulk along the windowsill. From inside the rooms, set the bottom of the insert replacement onto the sill, then tip it up into the opening. Press the window tight against the outer casings.
Hold the window in place with one 2-inch screw driven loosely through the upper side jamb and into the framing. The screw should be in just far enough to allow the window to operate. Close and lock the sash. Adjust the unit by inserting shims under the sill and behind the side jambs until it is centered in the space and opens, closes, and locks smoothly.
When the window is square, screw it in place through the predrilled holes. So as to avoid bending the frame. From the outside, measure the space between the window frame and the casing. Fill space with elastomeric caulk. On the inside, fill any gaps around the window with minimally expanding foam. Finish it up by reinstalling the stops or adding new ones. Then prime and paint.