When the old fashioned sash windows get older they become inefficient, draffy, and hard to operate, or the old wooden sashes begin to rot because of poor maintenance and need to be removed or repaired, even though the window frame is still in good shape. Sometimes a window sash replacement can help cure this problem by inserting new sashes into the existing window frames of the house. Several manufacturers offer sash replacement kits that provide new sashes and tracks to be installed into the old window opening. The tracks are screwed into the old frames and the sashes are mounted inside the new tracks. The process provides new sashes that are in good shape and are more energy efficient than the old sashes in the opening.

While this process may save material costs on the windows (not having to pay for a brand new window), it can be a labour intensive process, which will add to the bottom line costs and should be compared against full replacement. In addition, this process must be done correctly or the new sash replacement kit will not function properly which could lead to future performance and weatherproofing problems.

Old sash windows can have full frame replacements without removing the old frame or interior/exterior trim using a pocket window replacement. A pocket window replacement is performed by removing the old window sashes and stops and sliding a new window inside the pocket left behind by the old window. The window is then trimmed around the edges and sealed tight to guarantee a leak free installation. The benefit to a pocket replacement, in lieu of a sash replacement kit, is that the window is manufactured and tested at the factory so you know it is airtight, watertight, and energy efficient. By sliding the new window inside the existing opening, you are letting the window manufacturer worry about it keeping out the elements.

The window sash replacement will run you about the same as what you will pay for a new window by the time you factor in installation costs etc. so it can be a wash between the two options. If you get a low price for a window sash replacement, you should make sure the installer understands the amount of work required and that installing the kits correctly is the most important thing about the project.

Ultimately the decision to repair or replace a sash window is yours to make. Generally a replacement window is going to cost more than a simple repair to an existing window, but the long term benefits of a new window can surpass the benefit of just a "band aid" on an old one.

There are also many companies equipped to provide a replacement window installation than there are to perform a quality window repair. While you may save on the costs to fix a window, you might spend a lot of time trying to find the right person to perform the repair. The bottom line is this: when you are considering a window repair, you should also consider replacing the sliding sash window for the long term benefits that it can provide.