Core Sash Windows’ double glazed Sash Windows are specially designed to closely match the designs most famously associated with each of the Periods in which the Sash Window was fashionable, including the narrow profiles of their single glazed counterparts: elegant glazing bars, ovolo detailing, and curvaceous horns.

Our dedication to the conservation of London’s original aesthetics means that your replacement will be like-for-like, allowing you to enjoy the modern benefits of double-glazing, without compromising the appearance of your period property.


New Double Glazed Sashes In Renovated Existing Box Frames

Replacement timber double glazed sashes installed in renovated box frames (includes painting & draught sealing).




New Double Glazed Sashes In New Engineered Timber Box Frames

Replacement timber double glazed sashes & replacement box frames (includes painting & draught sealing).




The History of Sash Windows


A sash window comprises of two glazed sashes housed within a timber box frame, which are counterbalanced by heavy lead weights concealed within the frame. The lead weights are connected to the sashes by a cotton sash cord that runs over a pulley at the top of the frame.

As a staple of London’s architecture throughout the Georgian Period (1714-1837), the Victorian Period (1837-1901) and the Edwardian Period (1901-1910), the traditional sash window can still be found on almost every street in the city.

The varying designs available are indicative of the glass manufacturing techniques used during these periods, and the architectural fashions of the day. Sash window designs steadily evolved as the glass manufacturing techniques became less and less restrictive, and as a result, you can rather accurately date your home based upon the style of the original sash windows!


Georgian Period: 1714 – 1837
Window manufacture during this period relied on Crown Glass, a manufacturing technique that was only capable of reliably producing small individual panes. As a result, this period is famous for a high number of panes within a window, and popular designs were ‘6 over 6’ or ‘8 over 8’ styles. Most Georgian Period windows were incredibly symmetrical – both in terms of division of the individual sash, and the uniformity between top and bottom sash.
Victorian Period: 1837 – 1901
Sheet Glass manufacturing became more efficient in the 1830s, which overcame many of the limitations that had previously been caused by Crown Glass. This newly refined manufacturing process led to the production of far larger individual panes than was previously possible, or practicable, which led to a significant reduction in the number of panes needed within a window. As larger individual panes became more readily available, the popularity of ‘maximum glass’ designs skyrocketed, and this period saw the popularity of ‘1 over 1’ and ‘2 over 2’ designs.
Edwardian Period: 1901 – 1910
Glass manufacturing techniques did not dramatically change between Victorian Period and the Edwardian Period, however, the designs did not remain static, and window manufacturers began to experiment with far more ornate styles. There was often a staggering disproportion between the simplicity of the bottom sash and the complexity of the top sash. Bottom sashes tended to remain as plain ‘1 over 1’ or ‘2 over 2’ styles, whilst the top sashes began to implement beautiful curves and decorative ‘lights’. 



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Whether you'd like some expert advice, a free site survey, or just a chat about your options, we are always happy to help.

Unit 3 Marshgate Business Centre ,10-12 Marshgate Lane London E15 2NH

020 3302 2060 / 020 8519 2763



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