Now it has raised the alarm, the BRE is continuing its investigations, which may take some time. "The programme goes on to 2001," says John Sellar, head of acoustics at BRE. "We haven't got an answer yet. The next round of tests won't be complete until late August."
Time to get heavy
So what to do in the meantime? "We look at each site individually," says Peter Sanders, chief surveyor with Chase Midland Homes. "We have used sound deadening quilts, but we take the general view that it is mass of masonry that we should look for."
Sanders is well aware of the BRE research. "It's an issue we are looking at quite closely, but we have never had a problem with this in the past and we're not doing anything differently yet," he adds. At its Grange Park development, which is currently under construction in Barnt Green, near Birmingham, the housebuilder is using Bison Concrete Products' precast concrete flooring for a block of seven apartments and for 29 houses. "Where we are building bigger units of about 1600 ft2 we tend to use it. We have a fairly bespoke approach and the floors are part of that concept. Concrete gives us the flexibility of putting the walls where we want, whereas you have to be careful with timber, but we are happy with both systems and use both."
At Grange Park masonry mass comes from 7.5 N strength concrete, with 1800 kg mass blocks for party walls. "We are toying with the idea of going to 10.5 N concrete, but that is sledgehammer tactics," says Sanders. The housebuilder generally specifies 1200 mm-wide hollow core slabs with a depth of 200 mm, rather than the slimmer 150 mm option. At Grange Park they are combined with a floor screed, and a 100 mm battened and counterbattened ceiling void to accommodate downlighters and horizontal service runs. The housebuilder also keeps a close eye on site workmanship.
"I'm confident we have got the angles covered," says Sanders, and that includes taking into account essential services ducts between floors which can transmit noise. "We have to put intumescent collars around soil and vent ducts anyway for fire. We try to design ducts where they are out of the way - under wardrobes for example, so that they do not pose any problems. Beam and block flooring is not advanced technology, but it does need to be designed from day one. You need to establish where soil and vent pipes are running."
Sanders says Chase Midland has won benefits through using the flooring at Grange Park, notably in speed of build. The mansion-style apartment block has a complex design, particularly at roof level, which has taken 10 months to build. Use of precast flooring helped get the shell in place quickly, allowing maximum time for the more complicated elements. First and second floors each took around a day and a half to install. First apartments should be ready for occupation next month.
Banishing noise nuisance
Philip West, sales manager of precast flooring specialist Bison Concrete Products, points to the experience of housebuilders like Chase Midland as evidence of the good performance of his company's product. "The excellent sound resistance of hollow core concrete floors minimises noise nuisance from sound transmission and squeaky floors," he says.
The BRE has also this month published a manual* on sound insulation to guide housebuilders in correct design and site workmanship. The manual attempts to eliminate some of the confusion surrounding advice in Approved Document E, and gives advice on design problems not covered in the document.
Source
Building Homes
