Pvc Sash windows are very popular on period properties with their traditional design and classical appeal. There are two frames (or sashes), one above the other, that are situated in a box frame. One of the panes slides up and down and is held in place by a pulley. The pulley allows the heavy frame to be opened with relative ease and remain in place. There is no doubt that the older pvc Sash windows are draughty and are not great heat insulators. This makes houses with old style pvc Sash window the target of aggressive double-glazing salesmen. However, most people with period properties would rather keep the look and appeal of pvc Sash windows, than replace them with modern sealed units with PVC-u frames.
However, it is possible to upgrade older style pvc Sash windows to get both the classical look and the modern efficiency of double-glazing. These days many manufacturers make sealed units that are fitted into traditional sash frames.
There are also some alternatives to double-glazing for improving heat insulation and reduce noise. For example it is possible to get draught stripping systems. Alternatively consider fitting shutters which will provide an extra level of protection against heat and light and also give total protection against light if required.