Sliding sash windows have been a quintessential feature of British architectural history over centuries and many of these original timber windows are still in existence in homes and heritage buildings across the UK today.

The precise origin of the sash window is unknown, but they became widespread in 17th century Britain. The Great Fire of London in 1666 revealed the fire risks of casement windows, which opened outwards into narrow lanes. This spurred changes in the London Building Acts, which likely contributed to the popularity of the sliding sash window design. By the 18th century, sash windows were a hallmark of Georgian and Victorian architecture.

Preserving the timeless beauty and centuries-old craftsmanship of original sash windows in today’s world is vital for protecting our architectural heritage. “Did you know that, over the years, nearly 75% of the UK’s original box sash windows have been lost as a result of demolition, to make way for new buildings and new types of windows?”, one industry expert points out.

Who first introduced sash windows?

The esteemed British polymath Robert Hooke FRS (1635-1703) is widely regarded as the inventor of the sash window. Hooke frequently collaborated with Sir Christopher Wren, serving as his principal assistant. Together they rebuilt London’s streets following the Great Fire, working on iconic landmarks such as St Paul’s Cathedral, the Monument to the Great Fire, and Ragley Hall in Warwickshire. Hooke’s innovations in movable glazed windows played a vital role in shaping architectural design after the 1666 catastrophe.

The term ‘sash’ is thought to derive from the French word ‘châssis’, meaning ‘frame’. Early examples of sash windows appeared in France and the Netherlands. In Britain, sash windows swiftly became a signature feature of stately homes and royal palaces including Hampton Court and Kensington Palace.

One of the oldest surviving sash windows can be seen at Ham House, a spectacular 17th-century manor on the River Thames near Richmond, Surrey. Now owned by the National Trust, this historic house and its formal gardens are open to the public. Sash windows were an important feature during Georgian, Victorian and Edwardian times, so let’s focus on each period in turn.

Georgian sash windows (1714-1837)

Georgian sash windows first emerged in late 17th century London, becoming increasingly popular throughout the 18th century. Georgian architecture is known for its focus on symmetry and proportion, with windows and doors positioned to precisely mirror both sides of buildings.

These windows contained two sashes – one fixed top sash and a bottom sash that slid vertically using weights and pulleys. The glazing was divided into six or more small panes per sash, as glass production methods of the time made large sheets impractical and costly. Thin astragal bars separated the individual panes.

Key features of Georgian sash windows:

• Elegant, simple design
• Two hung sashes
• Six or more glass panes
• Typical six-over-six pane grid

Victorian sash windows (1837-1901)

Victorian architecture drew heavily on earlier Gothic, Tudor and Italianate influences. Under the guidance of acclaimed writer and philosopher John Ruskin (1819-1900), traditional forms were revived with modern materials to forge the future.

Sash windows were a key feature of Victorian homes, expertly balancing light, air, and weatherproofing. The Industrial Revolution enabled mass production of housing, creating millions of Victorian residences across the UK, many of which still characterise our towns and cities today.

Thanks to technological progress, glass sheets became cheaper and easier to produce. Victorian windows grew in size with fewer glazing bars dividing larger panes. Double-hung sash windows had two moveable glass panels that opened and a two-over-two grid became common. Intricate details like sash horns, stained glass and leaded lights were used to create stunning feature windows.

Key features of Victorian sash windows:

• Fewer glass panes
• Two-over-two grid pattern
• Single glazing bar
• Ornate designs e.g. curved tops, coloured glass

Edwardian sash windows (1901-1910)

Edwardian sash window design represented the pinnacle of box sash evolution in Britain, benefiting from advanced early 20th-century building methods. Edwardian architecture blended the best of Georgian and Victorian styles.

Typically, Edwardian windows had six panes on the top sash and one or two panes below, maximising natural light. The 1894 Building Act enabled bay and bow windows to be built on the ground floor rather than being restricted to flush walls.

Edwardian window design was heavily inspired by the Arts and Crafts and Art Nouveau movements, incorporating decorative mouldings, arched tops, and ornate accents.

Key features of Edwardian sash window:

• Six-over-one or two pane grid
• Large protruding bay windows
• Curved and bowed windows
• Elaborate mouldings and horns

Sash windows today and tomorrow

By the start of the First World War in 1914, the popularity of timber sash windows had begun to wane as hinged casement windows emerged that had a more modern style, were less expensive to produce and available in new materials including steel, cast iron, and later aluminium and UPVC.

As mass production advanced, casement windows in standardised sizes soon became the new norm for British window construction. Architects and builders embraced the flexibility of casement windows, which opened outwards and could be combined in wider configurations. Homeowners also appreciated the modern look and practicality of metal casements compared to draughty, high-maintenance timber sash windows. This shift in preferences meant that from the 1920s onwards, sash windows were no longer widely installed in new-build homes in Britain.

It is only in recent decades that sliding sash windows have regained popularity and appreciation. Historic properties retaining original sash windows are highly desirable to homebuyers who value the visual charm of these and other historic features and are prepared to pay a premium price for well maintained period homes.

As surviving examples become rarer, today’s homeowners recognise the skilled craftsmanship and care that goes into looking after timber sash windows. For homeowners lucky enough to own period properties with original sash windows, here are some tips for protecting them:

• Seek out qualified specialists for repairs, rather than attempting DIY. Skilled craftspeople can retain the historical accuracy and operation.
• Draught-proof and weatherstrip windows to boost energy efficiency, but use reversible methods that don’t damage frames.
• Consider lightweight secondary glazing to improve insulation without compromising aesthetics.
• Maintain paintwork to guard against rot. Use lead-free, breathable paints allowing wood to expand and contract.
• Check for warping, decay or sash movement issues. Early intervention prevents bigger problems.
• Clean glazing regularly and re-putty where needed to prevent damp and leaks.
• Keep mechanisms oiled for smooth operation. Counterbalance weights should move freely.
• Value authentic windows as heritage assets. Repair rather than replace, and avoid modern alterations like sealed double glazing where possible.

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