The research has led the HBF to propose nine standard wall constructions and four floor constructions that have been proven to comply with demanding sound regulations for new-build homes. They are called "robust standard details". Crucially, the proposals mean that any housebuilder using one of the standard constructions won't have to carry out expensive acoustic testing to prove compliance with the Building Regulations. If the government accepts the HBF's proposals – it is now consulting the industry – it will have a huge impact on the design of all new dwellings in England and Wales.
It might have been much worse for the housebuilding industry. In 2001, the government announced its intention of introducing compulsory acoustic testing of all new dwellings that incorporate a party wall or floor to prove that they complied with the acoustic regulations contained in Part E of the Building Regulations. The proposal meant that any housebuilder, even one constructing a pair of semi-detached houses or a small apartment block, would have to pay to have the acoustic performance of the building's walls and floors verified.
John Tebbit, industry affairs director at the Construction Products Association, says: "The original regulatory impact assessment [the government's estimate for cost of the regulations] did not reflect the real cost of on-site testing."
Housebuilders, worried about the delays that would result from having to halt noisy site work while testing was under way, lobbied hard to persuade the government to change its proposals. As well as the expense of conducting a test, they were concerned by the expense of failing it. If poor workmanship led to test failures they would have to be put them right at their expense.
So, instead of builders having to pay for tests to prove compliance, the HBF proposed an alternative: if they could demonstrate to the government that a set of generic wall and floor constructions complied with the new acoustic regulations, then any building built using these standard methods would be deemed to comply – and therefore be exempt from testing. This would save the housebuilders time and money and would eliminate the financial risk of having to put right any failures – a cost estimated to be £6-15m a year.
To ensure these robust standard details are sufficiently sturdy to comply with the regulations, they have been overengineered to reduce the risk of sloppy site workmanship. This makes them more expensive than other types of construction – the additional costs of using robust details are estimated to be £10.7m annually – but they do away with the risk of having to put right poor workmanship.
"The robust details will cost more, but they will remove any uncertainty on the part of the housebuilder," says Tebbit.
The advantage for the housebuilder is that the additional cost of using a robust detail can be quantified before construction. This cost can then be passed directly on to the homebuyer. Clearly, this represents a far less risky option, both in terms of cost and time, than having to site-test a building's acoustic performance and then correct failings.
The government accepted the HBF's proposal in July 2002 and gave the housebuilders nine months to come up with generic construction types. Originally, 36 wall and floor constructions were submitted for inclusion in the robust details programme, which was managed by the Building Performance Centre at Napier University in Edinburgh. However, a shortage of time, a lack of completed buildings ready for testing, and the fact that some proposals failed to meet required standards meant that only 13 robust details made it into the consultation document. Three construction types have since failed to meet the regulations and have been removed from the programme.
Because the robust details are generic, they do not favour a particular manufacturer and, as a consequence, have been accepted by most suppliers. "The process was designed to ensure no manufacturer felt disenfranchised. The robust details programme has gone out of its way to make the designs generic. So as long as manufacturers' products comply, they can be used in the robust details," explains Kendrick Jackson, managing director of housing consultant KJ Technical Services.
The government recognises that good standards of workmanship are still a key issue, even for housebuilders using a "robust" form of construction. To focus builders' attention on this need, the document proposes that all contractors using a robust form of construction must complete a checklist. For a wall construction, this asks the builder to confirm things such as the cavity width, density of the blocks being used and whether all joints are sealed. This checklist can then be used by the housebuilder to demonstrate compliance to building control officers.
As well as listing the first tranche of robust details, the consultation document puts in place a mechanism for further wall and floor constructions to be added in the future, including proprietary systems. This appears to have appeased most manufacturers. "The door is still open for other construction details to become robust details," says Cliff Fudge, technical director at block manufacturer H+H Celcon.
If the government gives the HBF the thumbs-up, housebuilders will be using robust standard details from January. And the CPA's Tebbit predicts that 80-90% of new buildings with party walls will be constructed using these rules. Maybe then, noisy neighbours will become a thing of the past.
Approved construction detailsWall constructions
- Aircrete block: Cavity wall, 75 mm cavity, nominal 8 mm render, 12.5 mm gypsum-based board
- Lightweight aggregate blockwork: Cavity wall, 75 mm cavity, 13 mm plaster-cavity wall, 75 mm cavity, nominal 8 mm render, 12.5 mm gypsum-based board.
- High-density aggregate blockwork: Cavity wall, 75 mm cavity, 13 mm plaster-cavity wall, 75 mm cavity, nominal 8 mm render, 12.5 mm gypsum-based board-cavity wall, cellular blockwork 75 mm cavity, nominal 8 mm render, 12 mm gypsum-based board
- Timber-frame timber wall, 60 mm mineral-fibre insulation both sides, no cavity-sheathing board, linings are two layers or more of gypsum-based board.
- Steel: Twin-frame metal wall, 50 mm mineral-fibre batt insulation between frames, no cavity sheathing board, linings are two layers or more of gypsum-based board.
- Concrete precast slabs: Minimum 150 mm precast concrete slab, 65 mm sand/cement screed (or proprietary 40 mm screed) bonded directly to slab, concrete-floating floor treatments and ceiling system.
- Concrete reinforced in-situ concrete: Minimum 250 mm reinforced-concrete slab with floating floor treatments and minimum 75 mm ceiling void and one layer of gypsum based board.
- Timber-engineered timber I-joist: Minimum 240 mm engineered timber I-joist, 15 mm sub-decking board, timber-floating floor treatment, resilient metal ceiling bar and two or more layers of gypsum-based board.
- Steel insitu concrete on metal decking: Insitu concrete slab, minimum 80 mm concrete cover to shallowest point, minimum 130 mm concrete cover to deepest point, using concrete-floating floor treatments, ceiling consists of one layer of gypsum-based board fixed by either timber straps, resilient metal ceiling bar or suspended metal-frame ceiling.
The consultation document is available on the government’s website: www.odpm.gov.uk.