In 1995 the Building Regulations were revised to improve the thermal insulation requirements. Under the governments Partners in Innovation Scheme CERAM conducted a questionnaire exercise before and after the change. Before the change was in force builders were of the opinion that, by and large, whatever they did they would not alter wall thickness. After the change larger builders had generally found a way to continue using the construction system that they were familiar with and wall thickness increased, commonly by 30 mm, to accommodate extra insulation. Smaller builders had tended to use the trade off options, for example using condensing boilers.
Insulation Performance Problems
More demanding thermal requirements led to increasing difficulty in finding materials for multi-layer construction that provided more than one aspect of the required performance. The Regulations were getting to the point that light materials were for thermal insulation and dense for sound insulation and structure. Compromises became more difficult.
The Single Leaf Solution – First Time Round
This led to CERAM revisiting an idea developed in the early 1980’s: single leaf insulation masonry. The system consisted of a single leaf of brickwork, closed cell thermal insulation stuck to the inside and plasterboard finish placed over the insulation. Initially, the outer leaf leaked and water dribbled down the inner face in the nominal cavity formed by the brick tolerances and the adhesive until it was channeled out by damp proofing details at the base. A lot of laboratory work was done, houses were built and tested and eventually sold, an attractive bungalow was built for the National Garden Festival. However the system was not a commercial success and there were one or two technical problems that were not well solved.
The Single Leaf Solution – This Time Round
CERAM have now addressed these problems. This time round wider (thicker) bricks are being used in order to make the walls more stable during construction. In the early 80’s acoustic tests showed that the party wall did not provide the acoustic isolation required by the Building Regulations at all frequencies. CERAM need to do better than this and, as a result, have built their own facility. Clearly, the detailing has been correct as the isolation is better than that required in the proposed improvement to the Regulations.
One result is that the rain penetration resistance of the wall is dramatically better than that of a half brick thick single skin. The reasons for this are not as yet fully understood, but if it is a real effect, the susceptibility of the construction to poor workmanship looks to be much reduced. There is much concern at the moment about the degree of restraint applied to a wall by a floor which is fixed to it using joist hangers, especially where competition between hanger manufacturers is leading to less metal being used and where I section joists make connection to the hanger difficult. The bricks used in the CERAM facility are 140 mm thick and 290 mm wide which means the central grip holes are at 600 mm centers, ie joist hanger spacing and make the perfect place for a downstand from the hangers bearing flange.
The next stage is to build a demonstration building at Roger Bullivant’s site in Burton on Trent. Bullivants have redesigned the ground beams in their pile and ground beam foundation system so as to suit the 140 mm structural wall and hence we have an innovative wall construction and compatible foundation system.
The aim now is to use the output of the project ie the designs with local housing associations to produce some badly needed new housing in Stoke.
Primary author(s): G.Edgell
Source: CERAM Research Limited
For more information on this source please email geoff edgell