The humble cavity wall is loved by builders and developers across the country and has been used in the construction of over three quarters of Britain’s homes. So how did this construction method come to dominate the British housing stock?
The early history
The basic principles of cavity wall construction – two leaves separated by a void – have been around since ancient times, with examples found in both Greek and Roman architecture. Like many other technologies however, the approach was essentially lost in time and it wasn’t until the early 19th Century that British architects and builders began to experiment with it in earnest.
The advantages of the cavity walled approach over the typical solid walled construction of the time were obvious. The outer wall acts as a barrier against the elements and works in tandem with the inner leaf to support the structure. The void, in turn, helps to prevent the passage of damp to the inner wall. As William Atkins observed in 1805, it could also be used to create buildings which are naturally “much warmer than any other kind” of common construction method of the time.
Despite its advantages, adoption of cavity or ‘hollow’ walls was relatively slow and by the turn of the century solid wall constructions remained the norm for most domestic properties. It wasn’t until the inter-war years that the approach really began to flourish. The Tudor Walters Report, commissioned by the Government to improve living conditions after the First World War, highlighted it as a useful approach and whilst local by-laws hampered its uptake in some areas (most notably the London Boroughs), by the 1940s it had become the predominant method of domestic construction in the UK.
Over time, several improvements were made in the construction method. For example, many of the early Victorian properties featured tight cavities and used bricks bonded in both leaves to tie the walls, allowing moisture to easily transfer to the inner wall. Eventually wall ties manufactured from galvanised metal were adopted and the inner brick wall was replaced with block work. This approach then remained relatively unchanged from the 1940s until the early 1970s.
Insulating the cavity
Thermal performance requirements for dwellings were first introduced in the 1965 Building Regulations, with external walls expected to achieve a U-value of 1.7 W/m2.K. The oil crisis of 1973, which saw the average barrel price rise by almost 400% in a single year, prompted further tightening and by 1975 exposed walls were required to achieve a U-value of 1 W/m2.K.
Cavity insulation was a natural solution for builders and architects faced with this new requirement. By fitting insulation within the existing void it was possible to conceal the insulation layer whilst also minimising any increases in the thickness of the external walls.
In this period, foam was typically used to partially or fully-fill the cavity but as successive building regulations have further tightened U-value targets, it has been necessary to find insulation solutions which boast ever greater thermal performance.
In the next week’s article we’ll take a closer look at the current requirements and approaches to meet them.