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What are Sash and Case Windows

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What are Sash and Case Windows

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Published on: June 24th, 2021

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Sash and Case Windows in Scotland

What are Sash and Case Windows? Sash and Case windows is the term for Sash Windows in Scotland. They are usually associated with traditional architecture and styling for older buildings, especially Listed buildings or those in conservation areas.

How are Sash and Case Windows Made?

Sash and Case windows consist of two vertically sliding window frames that are fitted with glass panes. The two framed window sashes are positioned one in front of the other and usually each sash covers just over half of the window aperture. In this way, one sash is positioned at the top, the other at the bottom with a slight overlap to seal the aperture completely. The window is opened by sliding one of the sashes vertically to create a gap. The great thing about sash and case windows is that they can create an aperture of almost half of the window size.

Each Sash in a sash and case window is made up of smaller panes of glass that are joined together by strips of wood, called Glazing Bars or Astragals. When glass making was in its infancy, only small panes of glass could be made, which is why sash windows were made up of lots of smaller panes. As the manufacturers got better and producing larger, better quality panes of glass, then sash windows had fewer and fewer panes of glass in them. 

You can generally tell the age of a sash and case window by looking at

  • The number of panes
  • The thickness of the window bars

Older sash windows could have anything up to 18 panes of glass in them.

History of Sash and Case Windows in Scotland

The older the window, the more panes and the thicker the window bars. True sliding sash windows in Scotland date from around the 1680s and 1690s. These revolutionary new windows had many panes of glass and chunky frames and window bars. The panes were made by blowing the glass into cylinders and rolling it flat or by spinning glass to create a flat sheet – that’s where the ‘bullseye’ panes come from. They are the centre of the pane and were cheaper than unblemished panes of glass, hence the widespread use in pubs. Windows that feature the bullseye panes are there to save money!

By the 18th Century window making technology had advanced to produce larger panes of glass with thinner frames and bars. By the mid 1700s the familiar Georgian style sash windows were available consisting of only 6 panes separated by very thin window bars. These windows were fitted with superior crown glass – glass blown into large bowl shape and flattened into a disk. Read more about crown glass on this Wikipedia page Sash windows with crown glass are very distinctive as the glass has curved ripples and a slight bellied effect. 

Sash and case windows in a traditional Scottish cottage
Sash and case windows in a traditional Scottish cottage

Glass manufacture advanced even further in the 19th century with the invention of plate glass. This enabled much larger windows to be made single panes. One of the hallmarks of architecture at this time was the huge windows that allowed natural light to fill rooms and brighten houses up. Ironically, there was a resurgence of smaller windows with more glass panes in the later part of the century, sometimes combined with larger panes. This style of a larger lower pane of a single sheet and a smaller upper sash made from many smaller panes, sometimes with patterns and stained glass, remained popular right up until the 1930s.

By the 1950s sash and case windows were falling out of vogue in Scotland. New houses featured casement windows from this time as they were cheaper, allowed more light into rooms and were generally in fashion.

Upgrading Sash and Case Windows

Home owners with older properties that have sash windows may want to improve the energy efficiency of their homes by upgrading or replacing their windows. Sometimes, older windows are just too rotten to be repaired and it is necessary to replace them. There are ways of improving the efficiency of these older windows that do not need to be replaced. These could include:

  • Replacing the panes with double glazed windows
  • Adding secondary glazing to the interior of the window
  • Installing draught stripping.

However – you may need to seek advice from your local Planning Department when replacing or renovating windows. Windows in Listed Buildings or in homes that are situated in conservation areas need special permission to upgrade their windows. This is to protect buildings that are of architectural historical significance – for example a building that has sash windows made with irreplaceable crown glass panes. This is called ‘Listed Building Consent’ or LBC. Planning officers much prefer repair to replacement of these important windows, however this is not always possible.

Heritage Sash and Case Windows

When repair of historic windows is not possible, Local Planning Authorities require the replacement windows to be as close to the original items as possible. This is a tall order, as modern windows are very different from their single paned forebears. It is entirely possible that a double glazed sash window could be made. However, the nature of double glazing is that it has 2 panes of glass separated by the insulating cavity. This gives us 2 problems:

  1. The windows will be much thicker than the original items
  2. The second pane will create a double reflection effect

The result – windows like these will not typically be approved by the Planning Officer.

Some companies – such as Gowercroft – build windows that will meet approval by planning officers. These are known as ‘heritage windows’.

Heritage Sash and Case Windows are likely to pass LPD approval

Constructed using ultra-thin vacuum insulated glass and modern timbers, heritage windows allow owners of listed properties to have modern performance from their windows without compromising the traditional styling. Well-made windows using materials such as Accoya® or Red Grandis are expected to last up to 70 or more years with the minimum of maintenance. These wood types are also less susceptible to heat expansion and contraction, so the protective paint layers remain intact for longer periods of time. These heritage windows will more than likely have specialised micro porous paint to increase the level of protection even more.

To find out more about the Gowercroft range of heritage and our classic range of sash and case windows, visit our products page.