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Architectural evangelism

This small but dynamic church extension is also a demonstration project for an innovative flooring system

Tucked into a back street just off Wallingford's historic market square is an extension to a church, a small but dynamic structure with a curved copper roof, steel walls and an innovative flooring system for which it has been selected as a demonstration project by the Movement for Innovation (M4I).

The market square and its environs is a conservation area that the local people and the South Oxfordshire District Council are justifiably proud of and assiduously protect.On the west side of the square is the Roman Catholic church of St John the Evangelist, built in the 1950s. It occupies a long, narrow site which includes a presbytery and garden.The church, formerly cold and poorly lit, has been refurbished by architect Dr Alex Amato; the new extension, built against the church's rear walls and on the former garden plot, contains sacristy, office, WCs and two muchneeded meeting rooms for Sunday schools and social gatherings.

Dr Amato has adjusted the complex geometry of the junction between the east and south walls of the church and the extension by inserting an asymmetrical high-level Planar glazed rooflight between them which directs light into internal rooms.

The copper roof sweeps down from the rooflight and extends over the east facade as a delicate aerofoil shape. This wall is a series of glazed aluminium sliding doors which can be slid back to dissolve the difference between inside and outside, creating a single generous space.

This simple extension has an additional agenda.Dr Amato is consultant architect to the Steel Construction Institute (SCI) for which he is involved in environmental research.'Architects ask me how steel can be environmentally friendly - I've set out to demonstrate how even a small and simple building can achieve this, 'he says.

'I've maximised the use of dry construction.A steel structure can be bolted together and the components can be reused or recycled when the building comes to the end of its useful life, reducing the embodied energy and the environmental impact. And this is achieved with walls, roof and floor which have U-values well above required insulation standards.'

The extension and church refurbishment are entirely of dry construction apart from the concrete raft foundations. A raft was chosen to overcome difficult ground conditions, including the church's inadequate foundations and the discovery of ancient burial sites.

In collaboration with Precision Metal Forming (PMF) and the SCI, Amato has devised an innovative dry flooring system using trapezoidal decking normally used for roofing, (see Working Detail overleaf ). The SCI and PMF are working together to develop ways of improving the composite action of this type of dry floor construction, which potentially could be extremely stiff, as well as addressing the acoustic and fire issues relevant to its use above ground-floor level.

The main roof structure is a series of of curved steel lattice trusses which create the delicate aerofoil shape of the copperclad roof. They are supported on laser-cut steel 'boomerang' arms mounted on 80 x 80mm RHS columns.The soffit is faced with timber slats and lined with acoustic insulation to deaden sound transmission.

The leading edge of the aerofoil roof is propped by a yellow-painted 'goalpost' structure of 254 x 254mm universal columns, connected by pig-nose bolts to laser-cut flanges welded to the top chords of the lattice trusses. A 'family' of robust connection details - paired laser-cut steel plates which slot over a central plate and are then bolted or pinned together - is used to connect the trusses to their support structure and to support the steel framework of the external timber deck.

The walls are of profiled steel, apart from the boundary wall to the north which had to be of masonry construction as a planning requirement.The use of steel - in a range of vibrant colours - was supported and encouraged by the local planning authority.Walls are formed of PMF sinusoidal profile Celestia finish with 125mm mineral fibre insulation and a PMF inner liner sheet.

Internal walls are formed of plasterboard fixed to the steel channel support frame, with a steel angle used as skirting.

The Celestia cladding was divided into 2.5m lengths (reflecting the structural grid) by projecting steel fins which support stainless steel climbing plant support rods.Wisteria and clematis will, in time, give a soft edge to these walls. A yellow bar spans between the fins at high level; window cleaners and maintenance workers can prop their ladders against it and avoid damaging the Celestia sill. Great care was taken during the design to ensure that the sliding doors and all other components were colour-matched with the 'Pegasus' Celestia cladding.

CREDITS

ARCHITECT Dr Alex Amato

STRUCTURAL ENGINEER Hyder Consulting John Haines

QUANTITY SURVEYOR Richard Keat Associates

MAIN CONTRACTOR Hinkins & Frewin (Oxford)

STEEL SUBCONTRACTOR LF Engineering

SUPPLIERS walls PMF Celestia cladding and lining sheet; insulation Rockwool; floor PMF trapezoidal roof deck; protective sheet Correx; PVF2 coating to doors Akzo Noble; external paving Marshalls

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