Sliding Sash Windows

Sliding sash windows have been a significant feature of buildings in the UK since the end of the 17th century. Our members manufacture sliding sash windows that match an authentic period feel with modern performance.

There are two types of sliding sash window designs:

  •  Box Sash – this sliding sash window uses cords, weights and pulleys to counter balance the sashes in the traditional way.
  •  Spiral Balance – instead of a weights and pulley system, the Spiral Balance sliding sash window uses spiral rod torsion and tension springs to bring the traditional window style into the 21st century. Many of our members provide a ‘tilt and slide’ version for easy cleaning.

For both the box sash and the spiral balance sliding sash windows, a number of period-matching design details can be incorporated. 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).


The thermal performance of sliding sash windows

In the past it was not possible to achieve good energy-efficiency without having over-thick glazing bars. With advances in technology, today’s double-glazed sliding sash windows 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 our members to make sliding sash windows with authentic slim, period profiles with A energy ratings or U-values as low as 1.4W/m2K.


Heritage designs for listed properties

For those properties that are listed or located in a Conservation Area, many of our members offer heritage designs for sympathetic replacement. These might incorporate putty-style glazing and specialist glass finishes to mimic the appearance of older glass. The type of design that these heritage designs might seek to replicate include:

  •  Georgian sliding sash windows – these typically had six to eight panes and large glazing bars due to the limited availability of good glass.
  •  Victorian sliding sash windows – these typically had fewer glazing bars due to larger panes of quality glass being available.
  •  Edwardian sliding sash windows – these tended to be more of a statement feature with ornate horn detailing.

For more information on Heritage windows, visit our Conservation Approved section.