Britain’s treasured stock of antique Georgian and Victorian housing was all built using single-skin walls. Now it could be about to make a dramatic return.
The traditional cavity wall is under threat from the most unlikely of directions – not from the makers of prefab pods or timber-frame systems, but from the brick industry and its partners.
What they have come up with is a single-skin masonry system called Traditional Plus. It consists of a single skin of masonry lined internally with waterproof insulation and fitted with an internal plasterboard finish. “It’s faster to build, I’m sure it’s cheaper and it gives the same performance as a cavity wall,” says Geoff Edgell of research organisation Ceram. “It’s a modern method of construction but it uses technology that people are already using.”
Edgell says the system will appeal to housebuilders. “This could be a very attractive system to them – bricklayers using the system didn’t ask for any more money to lay the blocks, which amazed us,” he says.
To prove the system worked, a two-storey test building has been constructed by Westbury Homes at foundation contractor Roger Bullivant’s yard in Burton-on-Trent. Edgell says the test showed that the single-skin system was structurally as good as a cavity wall building and Part A compliant. “There is less structure to build and the wind resistance of a 140 mm thick wall is about the same as a cavity wall.”
Edgell says the test house showed that single-skin construction was also water-resistant. “We’ve acknowledged wind-driven rain may get through the wall, but this will be channelled away [through weepholes in the brick skin] before it gets into the room,” he explains. “It performs extremely well in rain: after six hours of driving rain you only get a few damp patches on the inside of the brickwork.”
The system appears to have impressed local building control officers: “In Stoke-on-Trent, building control is keen to give it type approval,” says Edgell.
The team behind the product is hoping to put it to the test on a regeneration project in Stoke. The plan is to use the scheme to monitor time and cost compared with traditional construction – and to prove to the housebuilding industry that cavity wall is not the only option.
The history of Traditional Plus
Like most construction methods, single-skin brick walls are anything but new; entire cities in the Georgian and Victorian period were built with them. The cavity wall appeared only in the 1930s in a bid to stop wind-driven rain in exposed locations penetrating the wall and appearing as damp inside the building. The system was quickly adopted for most homes throughout the UK.
Things went well for the brick-and-block industry until timber frame started to gain ground in the 1970s. "At the time, the clay brick industry was very concerned about timber-frame construction," says Geoff Edgell of research body Ceram. "They could see timber being used on the exterior as cladding and worried that they would lose their market."
In 1980 the industry decided to respond to the threat by developing a single-skin brick system that would preserve brick's market position. The solution was based on an American design that used a single structural skin of 102 mm thick blocks. Water-resistant closed-cell polystyrene insulation was attached to the skin using dabs of adhesive. This provided a nominal cavity that could be drained in the same way as a conventional cavity wall. To prove the effectiveness of the system, two test houses were built on an exposed site. Edgell says the test proved that there were no problems with water ingress and structural performance. After the test, 15 houses were built using the system at Southend-on-Sea and a bungalow was built in Stoke-on-Trent.
Then in 1983 World in Action exposed how vulnerable badly constructed timber frame buildings were to rot and fire. "That programme was a big setback for timber frame and the need for the single-skin project went away," says Edgell. "Also, if you asked yourself who was benefiting from the system, there weren't great benefits for the homeowner or contractor."
The project was resurrected as a result of changes to Part L of the Building Regulations, which relate to energy use in buildings. The changes require a building's walls to be better insulated. In some cases this can result in the cavity in a cavity wall being filled with insulation, to enable the wall to comply with the enhanced regulations – defeating the cavity's original purpose. There is also a commercial attraction, in that the single-skin structural wall takes up less space than a cavity wall – even with enhanced levels of insulation – and means developers can squeeze extra square footage out of their precious land.
Traditional Plus is an improved version of the 1980s system. "Some mistakes were made about its commercial exploitation," says Edgell. "I personally felt 102 mm thick walls were relatively unstable and needed propping during construction, and there was a very fussy detail that connected the floor to the walls at first floor level." Traditional Plus uses 140 mm thick blocks for the walls, and a bespoke joist hangar and foundation system have been developed for it.