A comprehensive repair can dramatically reduce air leakage through existing windows—and air leakage is often the biggest problem with older windows. Repairs typically include installing new seals or gaskets where the sash and frame intersect. It also may involve replacing the putty, which holds the window panes in place; and sealing and insulating window counterweight pockets (in older double-hung windows).
While skilled homeowners can undertake the work, it is usually best left to specialized contractors. In Europe, consumers can find patented systems for upgrading existing windows, including the Ventrolla System and Quattro Seal, but in North America this work is typically done by specialized contractors—found in areas where historic home preservation is popular.