When single pane windows have been left without maintenance, they are subject to fall into disrepair and are then often perceived as being old and drafty rather than as the architectural assets they are. However, replacement windows are not necessarily the only alternative. The historic look and feel of the original wooden windows can be preserved with the option of transforming them from single to double pane glass. They won't look like much, if anything, has changed.
Wooden sashes, especially those found in older and historic homes, are likely to have been constructed of old growth pine. This type of pine has an exceptionally tight, straight grain which makes it particularly well-suited for an application that would have seen heavy usage over the years. Modern forestry growing techniques do not allow for production of the same quality of wood.
The transformation process is quite straightforward. First, the sashes are removed and the old putty is removed, as is the glass pane along with any muntins (wooden grill work). Then, the recess in which the single pane of glass was housed is routed out to make room for the two new panes of glass that will then create an insulated window by virtue of the dead air space in between them. The original muntins, if any, remain a part of the window on the inside. To complete the look on the building exterior, exact replicas of the muntins are applied on the outside of the window.
The dead air space between the two panes glass also acts as insulation. The warm inside air doesn't come into contact with the chilled, outside pane of glass, so condensation is prevented from occurring. Condensation is one cause of window decay. Moisture runs down the window and into the muntins as well as the frame and the stool. Over time, the wood begins to rot.
This procedure will not only improve the appearance of the window, but its energy efficiency as well. A single pane window may be responsible for as much as 25% of the heat lost during the winter months. Re-fitting the existing windows to create a double pane is one way to prevent older windows from being destroyed over time.