Double whammy

The Government has just announced that Part L's new tougher U values will come into force next February in one stage rather than the previously anticipated two Industry lobbying has influenced the final choice for walls (see box). "We have accepted that the U value of 0.30W/m2K for walls would cause an undue burden on builders and their materials and component suppliers in circumstances where European standards for declaring thermal insulation performance have yet to settle," construction minister Nick Raynsford said in answer to a parliamentary question earlier this month.

Part E poses its own challenges, particularly with its requirement for acoustic testing (see box). To add complications, Parts E and L are at odds in a number of areas and Part E in particular would seem to kick much of the Egan agenda into touch.

Areas of conflict
The main areas of concern for sound insulation remain the party walls and separating floors in multi-occupancy dwellings. In contrast, the thermal regulations tend to concentrate on the external envelope. To that extent, there is little specific conflict between Parts E and L. But the general drift of Parts E and L are clearly out of step.

Part E solutions for party walls favour heavyweight blockwork covered with wet plaster, both relatively skilled and traditional craft processes.

Brick and block remains capable of meeting the new thermal requirements in Part L comfortably, although they can be met equally easily with timber frame or other prefabricated build methods. The prospect of building a block of flats with prefab external walls and then using wet trades on the internal elements is, to say the least, perplexing.

But there is, buried in the detail of Part E, a resolution to this conundrum. While Part E boldly dismisses a number of popular techniques for walls and floors (such as beam and block floors and plasterboard on dabs), it is careful to include a number of lightweight framing details designed to cope with the new decibel reduction requirements. The problem for would-be prefabbers is that while these details are known to work well - they are widely used in hotels - they are expensive and thick. While modular torchbearers such as housing association The Peabody Trust may well take these details in their stride, it is much harder to see wavering homebuilders opting for prefabrication with such a significant cost penalty attached.

There is also concern over the junctions between party walls and floors and the external envelope - where the sound regs intersect with the thermal regs. These junctions are liable to give rise to flanking sound transmission, little understood and hard to design out. The Part E proposals draw on the extensive research done on flanking sound by the BRE and others and the document indicates several ways to successfully build these junctions, many of which involve adding a flexible cavity closer inside the external wall at its junction with the party wall or floor. This detail will ring alarm bells for designers working in the more exposed areas of the country where filled cavities are proscribed because of the risk of driven rain crossing through into the inner skin blockwork.

Mad Hatter's Part E?
Every survey that's been carried out into noise in the home has come to the same conclusion. Britain is becoming noisier and the British are becoming more troubled by noise. What is worse is that, according to a BRE estimate, 40% of new separating floors and 25% of new separating walls fail to meet the existing Part E standards for sound reduction which were formulated back in the peace and quiet of the 1950s. No one is arguing that the status quo is adequate but, in seeking to improve matters, the DETR has put proposals on the table which turn on their head established working methods.

The heart of the issue is the matter of pre-completion testing for multi-occupancy dwellings. The regulators are adamant that this is the only way to improve matters: the housebuilders are appalled at the prospect of expensive tests being carried out at such a late stage in the building process. Dave Baker, technical director of the House Builders Federation says: "We are happy to develop robust details but the supposition in Part E is that we can't do that. The DETR seems to think that acoustic testing is the only way to address these issues but we suggest that perhaps building control could inspect the workmanship. With acoustic testing, you have to wait until the unit is complete and if it fails the test, this involves expensive remedial work." Robust details have always been the preferred method of complying with Building Regulations. They give both designers and builders an easily understandable benchmark and by using them the construction is deemed to satisfy. But it has long been known that the use of robust details often fails to deliver the standards prescribed in the regulations. This is true of the thermal regulations where a theoretical U value of 0.45 frequently turns out to be rather closer to 0.6 and it is even more true of the sound regulations, as shown by the BRE survey.

Nick Antonio of Arup Acoustics thinks that the DETR is right to insist on testing: "Testing is the only way to improve building standards. Extra site visits by building inspectors won't be any good - it's notoriously difficult to spot sound problems whilst under construction. They really only show up under testing." What is actually being proposed in the Part E amendments is that a sample of party walls and floors are tested on each development. Acoustic testing doesn't come cheap. Baker comments: "Testing is slow and expensive with an average fee of around £2000 per unit, and it isn't clear how many homes we will have to test. On some sites it may be 100%." But testing may not be the panacea the DETR hopes for. For one thing, there is an acute shortage of accredited testers. Paul Howard, manager of British Gypsum's acoustic testing centre, comments: "I am worried about the standard of testing which will be required. The proposed rating scheme puts great emphasis on insulating against low frequency sound which is the hardest to measure accurately.

"There are currently only four or five UKAS accredited testing stations in the country, capable of testing at most eight sites a day. That's obviously not enough. There are dozens of acoustic consultants around who may step into the gap but they may not be up to the job." As the proposals stand at present, Howard's concerns are not addressed. There is no compulsion to use independently accredited acoustic testers: indeed housebuilders will be able to employ their own staff to undertake the tests. Nor do the proposals address the issue of undertaking alternative tests should the initial testing fail. The DETR, which administers MOT testing for cars, must be well aware of the wide variations in results from test measurements in other fields and yet it seems to be relying here on testing as the one way of making genuine improvements in the field of sound insulation between dwellings. The concern is that lax detailing will be masked by lax testing and that the new regime will thereby involve reams of extra paperwork, more professional fees but little real improvement in noise reduction between dwellings.