Sliding sash windows have been a significant feature of buildings in the UK since the end of the 17th century. There are many variations of design details, such as the proportion of the panes within each sash, the width of the rails and glazing beads, the profile of the mouldings and whether the top sash has ‘horns’ (where the side rails protrude below the centre rail to provide the sash with extra strength). Most sliding sash windows are double-glazed, although some members make them with triple-glazing.
In the past it was not possible to achieve good energy-efficiency without having over-thick glazing bars. Today’s double and triple-glazed sliding sashes use one glazing unit for each sash. Within the glass sandwich of the glazing unit there is a grid of spacer bars that exactly matches the glazing bars applied to the surface. The effect is indistinguishable from individually-glazed panes and allows us to make sliding sash windows with authentic slim, period profiles, yet with A energy ratings or U-values as low as 1.4W/m2K. Triple-glazed windows can achieve even lower U-values. See our Guidelines on Narrow Cavity Insulated Glazing Units for advice on slimline double-glazing.
Box sashes, using lead weights and pulleys are the traditional choice, but where space is limited, a modern spiral balance version is available.
One of the disadvantages of the sliding sash design is the difficulty of reaching all areas of the window from the inside for cleaning or re-decoration. Tilt and Slide versions overcome this problem; although the panes slide up and down like a normal sliding sash window, a catch allows them to be released so that they can be opened into the room.
Hardware can be traditional or modern. Windows can be supplied with locks, opening restrictors and enhanced security to meet Secured by Design standards.
See the Conservation area windows for more information about sliding sash windows in Conservation areas or for listed buildings.