What are Sash and Case Windows?
In Scotland, “sash and case windows” is the term used for what is commonly known elsewhere as sash windows. These are typically found in older buildings and are strongly associated with traditional architecture, especially in Listed buildings or conservation areas.
How Are Sash and Case Windows Made?
These windows consist of two vertically sliding frames fitted with panes of glass. Each sash typically covers just over half the height of the window opening. One sash sits at the top, and the other at the bottom, with a slight overlap to fully seal the opening. When opened, the sash slides vertically to allow ventilation up to nearly half the window height.
Each sash is often made up of several smaller panes of glass, joined together by thin strips of wood known as glazing bars or astragals. In the early days of glassmaking, only small panes could be produced, which is why early sash windows featured multiple smaller panes. As manufacturing techniques improved, windows began using fewer, larger panes.
You can often estimate the age of a sash and case window by:
- The number of individual panes
- The thickness of the wooden glazing bars
Older sash windows sometimes featured up to 18 small panes.
The History of Sash and Case Windows in Scotland
True sliding sash windows began appearing in Scotland around the 1680s–1690s. Early versions had chunky frames and multiple small panes made using methods such as blowing glass into cylinders and flattening them—or spinning glass into discs, which created the iconic ‘bullseye’ panes. These bullseye panes were more affordable and became common in places like pubs.
By the 18th century, improvements in glassmaking led to thinner frames and fewer panes per sash. By the mid-1700s, the now-familiar Georgian sash windows with six large panes and fine glazing bars were widespread. These featured crown glass, blown into a bowl and flattened into a disc. Crown glass gives a distinctive rippled or slightly bellied appearance. Learn more on Wikipedia.
In traditional Scottish cottages, sash and case windows were everywhere.
In the 19th century, plate glass was developed, allowing much larger panes and creating brighter interiors. Later in the century, smaller panes returned in fashion—often featuring decorative upper sections with patterns or stained glass. This mix of large and small panes remained popular into the 1930s.
By the 1950s, sash and case windows fell out of favour in new builds, replaced by more modern casement windows that let in more light and were less expensive.
Upgrading Sash and Case Windows
Homeowners looking to improve energy efficiency may want to upgrade or replace old sash windows. In some cases, the timber is too decayed for repair.
Options for improving efficiency include:
- Replacing panes with double glazing
- Adding secondary glazing inside the window
- Installing draught stripping
However, for Listed Buildings or properties in conservation areas, planning permission is required before making any alterations. This is known as Listed Building Consent (LBC). Local planning authorities often prefer repair over replacement, especially when original features like crown glass are present.er repair to replacement of these important windows, however this is not always possible.
What Are Heritage Sash and Case Windows?
When historic windows can’t be repaired, replacement windows must closely match the originals in appearance and style. This is difficult with modern double glazing, which creates two problems:
- Thicker profiles than traditional windows
- Visible double reflections due to the extra pane
These issues mean many standard double-glazed windows are not approved by planning officers.
However, companies like us design windows specifically to meet heritage requirements.
These are known as ‘heritage windows’.
Why Heritage Sash and Case Windows Are More Likely to Pass LPD Approval
Using ultra-thin vacuum insulated glass and modern timbers like Accoya® or Red Grandis, these heritage windows deliver modern performance while keeping a traditional look. These timbers are highly durable, stable, and require minimal maintenance.
Key benefits include:
- Lifespans of up to 70+ years
- Reduced warping and expansion due to timber stability
- Micro-porous paint finishes that protect the frame and extend the window’s life
Interested in Heritage Windows?
Gowercroft offers a full range of heritage and classic sash and case windows. Visit our products page to learn more.