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Austin Williams writes:

technical & practice - feedback

Early misinformation by the Office of the Deputy Prime Minister (ODPM) overstated difficulties with beam and block floors, in particular the flanking transmission (sound carried through to another room via elements that are not separating walls or floors or via other indirect transmission routes).

Some slab manufacturers have repeated the assertion of the ODPM (guided by the BRE) that 'no satisfactory beam and block solution has been found'.

The correct situation at the moment is that field tests are ongoing as part of the process of developing House Builder Federation (HBF) Robust Standard Details, which include standard details for beam and block flooring. To overcome flanking possibilities, manufacturers recommend that an off-the-shelf 300mm precast concrete plank (or in situ concrete strip) be laid alongside the walls to eliminate any weak points.

Ian Carling, secretary of the Beam and Block Alliance, says: 'Once someone applied themselves to finding a solution, it quickly materialised Field tests are ongoing and [compliance is] viewed as a formality.'

Since the HBF 'measurement phase' for all Robust Standard Details is not due to be competed until the end of March, we have to rely on the statement from the BRE's preliminary results last year.

John Salter, head of Acoustics Centre at BRE, said: 'The initial results of tests of the modified beam and block products were encouraging and are now ready for testing in the field.'

Craig Barron, senior consultant at HBFaccredited acoustic testing facility Sound Research Laboratories, said in July last year:

'We initially tested the modified floors in the laboratory without flanking and achieved a figure of 64dB Rw , providing, as we expected and as forecast by BRE, that the floor itself performed extremely well. We then tested several variants of the proposed new detail with flanking in a mock-up of a house built to the new regulations.

This achieved very good levels of D nTw + C tr ofbetween 50 and 51dB.'

This corresponds favourably with the Approved Document airborne sound insulation minimum value of 45dB (43dB for dwelling houses formed by material change of use).

In general, we understand that the HBF has already prepared several RSDs on beam and block floors and that, as usual, the inflated concerns about the construction industry not being able to cope with new compliance criteria are groundless. Beam and block, it would seem, is here to stay.

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