Tests on the acoustic performance of composite deck floors show many easily outperform current standards
Acoustic performance is increasing in importance in residential specifications as developers and occupants demand higher standards. The Building Regulations for residential buildings include minimum standards of acoustic performance for walls and floors between dwellings (separating walls and floors), and these are due to be upgraded in 2002/03. The government recently announced that it intends to introduce mandatory testing of a sample of all dwellings at each site, although Robust Standard Details may be allowed as an alternative way of showing compliance.
Hot-rolled steel framing with composite floors is increasingly being used in residential apartment buildings and mixed-use developments where the benefits, which include speed, quality and off-site prefabrication, are important. In order to demonstrate the acoustic performance of steel frames with composite floors, the Steel Construction Institute has been collecting acoustic test data from steel-framed residential developments in the UK.
Tests have been carried out on two buildings using Slimdek construction with ASB beams and deep-profiled decking, and in two buildings using shallow-deck composite floors with downstand beams. These are generally in city-centre locations and are either mixed-use developments of retail and commercial space with residential above, or freestanding medium-height residential blocks.
One example of a Slimdek residential building is an eight-storey development in Glasgow that consists of 49 high-quality apartments, including a penthouse and eight duplex (two-storey) apartments. The composite floor consists of 280mm asymmetric Slimflor Beams using 225mm deep decking to give a 300mm deep composite slab with a resilient floor and suspended ceiling.
For a high-profile 19-storey steel frame residential development in Manchester, consisting of 84 apartments and four penthouses, the developer specified acoustic standards considerably better than Building Regulations. The chosen construction was of the type used in many multi-storey steelframed commercial buildings. It consists of a hot-rolled steel frame with downstand beams supporting a composite steel deck floor. This has a floating screed and plasterboard ceiling The acoustic test results (as summarised in the table opposite) show that such floors can easily achieve acoustic insulation standards considerably better than those required by current and proposed future regulations. In the Glasgow building, the average airborne sound insulation (D nTw ) was found to be 62dB. This compares very well with the minimum acceptable in the Building Regulations - 52dB. The average impact sound transmission (L' nTw ) was found to be 48dB, which also outperforms the Building Regulations requirement of less than 61dB by a considerable margin. The building in Manchester also performed impressively. The D nTw wasfound to be 65dB and the L' nTw was found to be only 45dB.
These test results are also considerably better than the requirements of the optional 'Enhanced Acoustic Standards' set out in a recent BRE publication 1for developers who wish to specify a standard higher than that imposed by the regulations. They also considerably outperform the proposed standards for the revised Building Regulations.
With any type of construction, good acoustic performance is dependent on good detailing and effective site practices. SCI and Corus plan to carry out further acoustic testing of steel-frame buildings with composite floor slabs and to publish guidance on detail design for achieving good acoustic performance.More information is available in SCI case studies on Slimdek 2.Mark Gorgolevski is an architect and environmental consultant
1 Specifying dwellings with enhanced sound insulation - a guide, BRE, 2000
2 Case Study 4, Data sheet 1, Case Studies on Slimdek, Steel Construction Institute, 2002, Publication P309
The Building Regulations 2000: Proposals for amending Part E - Resistance to the passage of sound, DETR 2001