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Update on steel Recent steel developments include new uses for light- gauge framing and improved thermal, acoustic and fire performance

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'Until recently, almost all of the better steel-based architectural examples were found abroad. But there are now uk initiatives.'; technical & practice

British Steel recently launched Design Futures, spanning product design and urban design with a focus on sustainability.

For product design (under the aegis of the British Design and Art Direction Association), this covers products in the fields of transport, public spaces, health and leisure, work and the home. The Design Museum's Sustainable Design competition (sponsored by British Steel) will identify and reward world-class examples of products and buildings that improve the quality of people's lives and meet the most stringent criteria of sustainability.

Living In The City is an ideas competition for a dense, large-scale project for urban living, incorporating mixed-tenure housing and a variety of urban facilities. Entries should promote sustainable development and innovative construction. The competition is organised by the Architecture Foundation, along with the Peabody Trust and Railtrack. While the use of steel in the competition is encouraged by British Steel, it is not a prerequisite for success.

Such light steel construction systems normally use three technologies: individual C or Z-shaped stick-building components made from galvanised steel strip; prefabricated wall/floor/roof panel assemblies; and modular or volumetric technologies.

Sustainable accommodation can be attractive, architecturally and commercially. Until recently, almost all of the better steel-based architectural examples were found abroad. But there are now uk initiatives in steel by Piercy Conner, Tom Meikle, Minale Tatersfield, Cottrel and Vermuelen, and Cartwright Pickard.

Performance tests

The Steel Construction Institute (sci) recently completed a series of tests on light-steel framed dwellings to establish its as-built thermal and acoustic performance.

Typical light-steel-framing floor and wall constructions of occupied dwellings can achieve acoustic insulation standards well above the

current Building Regulations requirements of 53dB for walls and 52dB for floors (minimum airborne sound-level difference) and 61dB for impact sound (maximum received). Light steel can achieve 60-65dB for walls, 55- 60dB for floors and 50-55dB for impact sound. Thus it also meets requirements proposed in the review of Part E of the Regulations.

Thermal insulation values of 0.2 W/m2K are readily achieved in light steel construction using two layers of closed-cell insulation. Thermal- performance tests included air leakage through the envelope since air infiltration is becoming the dominant heat loss (up to 40 per cent) from new dwellings. The results confirmed that thermal bridging is avoided by using the warm-frame principle, with insulation placed on the outside of the steel frame. The collected data are now being used to inform detr amendments to the Regulations.

Light steel refurbishment

According to Mark Lawson, head of building research at the sci, light steel framing has found a niche in the renovation sector. In particular, the over-roofing and over-cladding of buildings is growing in the uk, using techniques pioneered in Scandinavia.

Over-roofing is the creation of a new roof structure for an existing building. It can be a 'cold roof', in which a new, weather-protecting pitched roof covers a flat one. Or it can be a 'warm roof' in which a new insulated enclosure provides an envelope around additional habitable space. Light-steel framing imposes little load on the existing structure and its foundations. Often, the increased property value/income created by the new space can pay for the work. Over-cladding is the attachment of new cladding directly over an existing facade. It can reduce fabric heat losses, improve appearance and stop deterioration of the existing building. It cuts disruption to occupants during construction. The galvanised light-steel supporting-framework has a design life of more than 60 years and offers a cheaper alternative to stainless steel. Tests at London's Imperial College found that environmental conditions in the cavity behind the new facade do not lead to a risk of condensation.

Modular or volumetric units are being used to renovate and extend existing buildings. They are self-supporting vertically but are supported laterally by the existing structure. Examples of such units include: new wc and bathroom units; balconies and access ways; lifts and stairs; and roof- top extensions.

Of course, all modular units are reusable and recyclable. For example, the new McDonald's Restaurant at the Millennium Dome is based on 51 light- steel volumetric modules. This 500-seat restaurant and retail outlet, which is manufactured by Yorkon, will be dismantled after the exhibition has ended and be used as eight modular drive-through restaurants around the uk - a veritable fast-food takeaway.

Fire-engineering uses

The headquarters for ttp Group, designed by Bland Brown and Cole, is nearing completion in Cambridge's Melbourne Science Park. It uses fire- engineering techniques to eliminate the use of site-applied fire treatments, without the need to introduce compensating active protection measures. These techniques are detailed in a new sci publication, Design of Steel- Framed Buildings without Applied Fire Protection (see page 42). Techniques include composite columns in the perimeter walls, use of in-filled concrete tubular columns inboard and a Slimflor composite-floor system.

Conventional composite construction might be used unprotected in future where fire ratings of one hour, or perhaps more, are sought. This could be a significant turning point in design against fire.

Peter Trebilcock is principal architect at Amec Design and a consultant architect to the sci.

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