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How townhouses keep evolving to meet their resident's needs


Secondary Glazing in Practice


acoustic secondary glazing, retrofitting, heritage

Residential squares were originally designed to bring a natural space into the heart of the city. Now, they are often used as a shortcut with nature all but drowned out by the far less dulcet tones of the carbon combustion engine. Built as homes for Londoners throughout the 18th and 19th centuries, the quintessential London townhouse is modelled on classical architecture. Its large symmetrically spaced windows flood the interior with light  and help create the Georgian style. However, inherent in their design is an acoustic weakness through which 21st-century urban noise cuts straight through! London's residential squares reflect the changes in culture, architecture and construction over the centuries; with windows being a particularly revealing element. This process of evolution is still progressing although you’ll need a particularly eagle eye to spot it! Material constraints of sash windows 
History early 18th century sash
Early Georgian style townhouses have sash windows built flat to the external face of the building. The construction of early sash windows was constrained by the sheer thickness and weight of glass. During the late 17th and 18th centuries windows were glazed in Crown glass. This required many glazing bars which could be as thick as 35mm, cutting down the amount of glass in each sash significantly.  Legal restraints on sash window placement
Late 18th century sash window
To reduce the possible spread of fire the 1709 and later 1774 London Building Acts required the box sash to be set back and ultimately hidden behind the masonry of the reveal. Gradually, as glazing technology advanced, windows could be made with glazing bars as thin as 10mm and with a significantly larger proportion of glass to timber.  Popular taste also plays its part as the now ubiquitous white exterior of windows were originally black, whilst opulent houses often sported black frames embellished with gold leaf! Black exterior decoration 18th century Black exterior paint – Original colour scheme in both the 17th and 18th century By their very nature sash windows have poor acoustic properties. Counter balanced, double-hung sashes are designed to glide smoothly. To achieve this, each sash needs to have room to move within the sash box and it is this 'wriggle room' which reduces the acoustic properties of the frame allowing soundwaves to pass through the gaps. Whilst the large single glazed glass surfaces of each window allow soundwaves to easily pass through. Acoustic secondary glazing forms an airtight seal, allowing no soundwaves to penetrate through its frame; whilst the air gap between the primary and secondary window decouples the two glass surfaces, deadening the sound within the cavity between the two. To gain even more sound reduction, acoustic units are designed to hold thick acoustic glass which further deadens sound transmission. Content images for sash window history Holburne museum Georgian façade and example of low impact thermal/security secondary glazing - Holburne museum With many thousands of Listed properties in London and with a significant proportion of these suffering from sound ingress, acoustic secondary glazing is often the only solution. Accepted by the vast majority of conservation officers, secondary glazing has proved to be invaluable in restoring peace and tranquillity to special buildings. Selectaglaze is proud of both the benefits and the aesthetics of its product. Now the evolution of the iconic townhouse involves low visual impact adaptations which transform the acoustic properties of the original. However unlike their predecessors these 21st century adaptations are very hard to spot...can you?