Old basement windows can be a source for unwanted groundwater to enter a home during the rainy season. Sometimes, the best choice is to replace basement windows with a newer replacement model. Although, most basement windows are fairly easy to replace, following some general guidelines will ensure that you end up with a waterproof and draft-proof window that adds light and style to your basement and walks you through window instillation.
Check with the building authority in your city or county. Due to fire safety regulations that were enacted during the 1990's, you must replace an existing basement window with an approved egress window that will provide an escape route from your basement. Depending upon the code, this usually means choosing a slider.
Remove the old window by prying the trim off from the exterior of the window and pulling out the nails that hold the window in place. Repeat the process from the interior of the home to free the old window from the frame. If the window doesn't come out easily, use a flat bar to gently pry at the top corners.
Inspect and repair any rotting wood or termite damage at this time.
Begin window installation by inserting the new window in the frame from the outside. It helps at this point if you have an assistant standing on the inside to make sure the placement of the window unit is even. The assistant will check to ensure the gaps on either side of the window as well a replaces those above and below it are approximately the same.
Nail one bottom corner in the attached flange and then use a carpenter's level to determine the bottom window level. This is done before nailing the other side. Continue to nail the remaining holes provided in the attached flange.
Select a storm window or attach weather-resistant trim to the exterior of the basement window. Treated wood is a good choice but resin-based composite materials provide a waterproof finish that will last indefinitely.
Push fiberglass insulation in the gaps surrounding the window from inside before installing the inside trim. Pack loosely. Insulation needs a "dead space" in order to trap the air. For this reason, avoid expanding foam insulation around windows.
Install the new interior trim and fill nail holes with matching putty and paint or varnish. On the outside, use silicone caulking to fill seams and paint, if desired.