Windows: Installing a Sash Replacement Kit

Sometimes a window can be improved considerably without replacing the entire unit. Several manufacturers make kits to replace just the sash, so you don't have to replace the existing jambs and casing. This option is particularly helpful if there is no need to change the size or location of the windows.

Energy efficiency will improve significantly when you replace a single-glazed sash with a new double-glazed sash. Sash kits also include new tracks, called jamb liners, to hold the sash in place. These liners reduce air leakage around the sash, and also make it easier to raise and lower the windows. Another advantage of replacing just the sash is speed: The work goes much faster when you don't need to remove the entire window unit.

The most important step in the process is measuring existing windows carefully. The exact places to measure, and the tolerances, will vary from manufacturer to manufacturer, so decide on the brand of replacement sash before getting started. Generally, however, measure the width and height of the jambs (not including any stops), and the opening for any screens. It is usually helpful to make a sketch of the window to show exactly where measurements were made. (Fig. 1)

It may also be necessary to measure the sill angle to ensure that the new lower sash seals properly against the sill. This measurement can be made with a sill-angle finder. (Fig. 2)

1) Remove the sash and stops
Starting from the inside of the house, the order of removal is as follows: inside stop, lower sash, parting stop and upper sash. Depending on the window, it may be necessary to remove an outer stop. The stops can be pried from the jambs with a small pry bar (Fig. 3). There's no need to fill the nail holes since they'll probably be covered by the new jamb liners, but it is necessary to scrape away any ridges of built-up paint that could interfere with proper placement of the liners.