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At the water's edge

working details: A copper-roofed boathouse by McAllister Co in London's Battersea Park is a simple and robust modern building

McAllister Co has designed a new boathouse of greenheart timber, steel and unpatinated copper which appears to float over the water of the boating lake in Battersea Park, south London.Made of natural materials and simple, robust construction, it is part of a larger restoration project in the park which is funded by the Heritage Lottery Fund.

Battersea Park, with its lakes, was designed by John Gibson, a pupil of Joseph Paxton, and opened by Queen Victoria in 1858. Covering more than 80ha on the south bank of the Thames, it was one of the first public parks to be established in the UK as 'a lung for the city', in the hope of improving public health and living conditions. It made a more practical contribution to the wellbeing of London when, during the First and Second World Wars, it was turned into allotments and a pig farm. Part of the site was taken for the Festival of Britain pleasure gardens in 1951, but it is still surprisingly large and verdant. It is now being restored to its former glory and some of the more dilapidated buildings are being replaced.

The boating lake is a major attraction in the park. It has boats for hire, and a cafe in which to sit and watch them. The boathouse, in a picturesque setting bordered by mature trees, terminates the new boardwalk which borders the lake. It houses an aluminium rescue boat, a small workshop, boat-parts storage and a sound-proofed chamber for the compressor which blows air into the lake to aerate the water and maintain a healthy environment for fish.

McAllister's design is elementally simple.

'The building had to be robust enough to withstand vandalism, especially at night when the buildings are unsupervised, ' he explains, 'but we also wanted it to be timeless, well-proportioned and have an integrity which comes from honesty of construction and materials.'

The building is triangular in section - a pitched roof overhangs the lake on one side.

It is made of unpatinated copper sheets with standing seams, supported by a series of greenheart trusses. The concrete compressor chamber inside it is painted ox-blood red - a traditional Victorian colour - to match the Victorian concrete kiosk, where the boats are hired and paid for, at the other end of the boardwalk. At each end of the boathouse are large sliding doors which are made of 150mm balau boards - the same width and material as the boardwalk. The doors are designed as an integral (and moveable) part of the landscape, opening and closing like an 'in/out' sign and allowing views into and through the building when open. They hang from a galvanised steel 'goalpost' structure.

The new boardwalk, more than 100m in length, has been designed by the architect. It consists of planks of 150 x 28mm balau, a yellowish hardwood, which are the same as those used on the sliding doors, but grooved to give grip. They are fixed to the joists below with exposed stainless steel coach bolts with countersunk heads. Rather than follow the curve of the lake shore, the planks are laid orthogonally, so that they align with the door of the boathouse. The result is a seamless integration of architecture and hard landscape, an aesthetic pleasure which should add to the attraction of boating on the lake.

The boathouse rests on concrete pile foundations. A concrete raft supports the cast in situ concrete compressor chamber;

concrete was chosen for security and so that the noise of the compressor would not disturb the tranquillity of the lake. Two 350mm-diameter air-supply ducts lead from the chamber roof to the gables to supply the compressor with fresh air, and to extract fumes.

A simple three-bay boxframe of 254 x 146mm galvanised steel universal beams supports 12 triangular trusses of 200 x 100mm greenheart, a sustainable hardwood which is suitable for damp conditions. The trusses are fixed to projecting lugs bolted to the beams. The trusses, in turn, support 100 x 100mm treated softwood purlins and 100 x 75mm treated softwood joists.

The roof finish - 0.6mm copper sheets,600mm wide and jointed with standing seams - lies on a geotextile fleece and 25mm birch-ply deck. Rainwater is directed by the standing seams and runs off the roof into the lake.

The sliding doors are made of butt-jointed balau boards framed with galvanised steel flats and angles. Each door weighs 300kg and is opened with a massive cleat of the type used on sailing yachts.

The steel 'goalpost'which supports the sliding doors is fabricated from paired 260 x 75mm PFCs (parallel flange channels) fixed back-to-back with a fixing cleat between.

The space between the channels conceals the slidingdoor gear.The goalposts are bolted with 10mm steel plates to a pair of 254 x 146mm universal beams which extend from the three-bay box-frame.

The gables above the door openings are faced with hardwood louvres lined with stainless steel mesh.

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