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A game of two halves

Extending a Denys Lasdun building calls for a tricky blend of architectural tact and assertiveness. Tact, because the creator of the National Theatre was one of the architectural giants of the last half-century. Assertiveness, so that any extension would not be totally swamped beneath the bold brutalism of Lasdun鈥檚 building.

Liverpool University鈥檚 sports centre is a case in point. Though built to Lasdun鈥檚 design in 1966, it is in truth more of an architectural rogue than a masterpiece. It is basically a grey, concrete box that disrupts the regular, Georgian street pattern next to Abercrombie Square. Yet it does attain a bold, iconic form, like a truncated ziggurat with inward-raking external columns and window walls along front and back.

To architect Austin-Smith:Lord, which was asked to add another sports hall to the building, the natural inclination was to extend the building beyond one of its vertical sides of windowless, concrete panels. This, says director Alistair Sunderland, would be like extruding the building鈥檚 ziggurat form, and would at the same time make good the original street line.

The problem was that the set-back from the street was too shallow to fit in a standard sports hall. The only feasible option was to extend the building out from one of the inward-sloping sides.

The hitch with this was how to link the rectangular box of a new sports hall with the inward-sloping side of the existing building. The existing sloping wall could not be reconfigured as a more neighbourly vertical wall, because the raking columns made up the building鈥檚 primary structure. So the solution conceived by Austin-Smith:Lord and structural engineer TD Bingham (formerly Roy Billington Associates) was to support the new building off two rows of A-frames, running along either side.

At the critical interface between old and new, one set of legs of the A-frames duplicates the existing raking columns. Each of the new legs rises just 100 mm beyond one of the existing columns at the same 72掳 angle, and with a similar cross-section of 250 mm x 150 mm. The subtle difference is that the existing legs are made of reinforced concrete whereas the new ones are hollow steel sections.

At the opposite external side of the extension, the A-frames are dynamically expressed as an external collonade. As well as forming a covered walkway, they echo both Lasdun鈥檚 ranking columns at the opposite side of the building and also the conical roof of Frederick Gibberd鈥檚 Roman Catholic cathedral nearby.

As for the roof, Sunderland wanted it to sag slightly towards the middle, to mirror Lasdun鈥檚 building. Here again, the visual effect is a perfect expression for the structural system. The roof functions quite simply as a canopy or awning slung between the A-frames on either side. Its sagging form actually increases its structural efficiency, as it has been allowed to assume a catenary curve, or the stress-free shape of a chain hung loosely between two points.

Brian Edmundson of TD Bingham prefers the analogy with a blanket held by fireman to catch people jumping out of a burning building. 鈥淭he more they allow the blanket to sag, the weaker is the grip they need on it. So the catenary curve in the roof puts less tension on the A-frames and their foundations than a flat roof.鈥�

Internally, the next extension is mainly taken up by the four-court sports hall. The changing rooms and toilets occupy a buffer zone between the new and existing buildings, and a fitness suite has been created above them.

Being nothing more than a rectangular box, the interior of a sports hall comes with little scope for architectural expression. Here, however, the most is made of an array of special 鈥� if inexpensive 鈥� features. As well as the outward-sloping side wall, they include a tactile lining of natural, birch-faced plywood panels. Lighting from uplighters bounces off the white, parabaloid roof surface, across the sports hall and into the fitness suite next door, while daylight filters in through clerestorey windows at each corner.

Partly because of the additional facilities in the 拢2.7m extension and partly because of its clean, crisp image, the number of students joining the university sports club has shot up fourfold. In architectural terms, it splices neatly into the existing building, while also providing a suitable visual foil to Lasdun鈥檚 rogue architecture. And by clearly expressing its structural form, it manages to score points over Lasdun. All in all, a well-judged balance between tact and assertiveness.

Project team

client University of Liverpool
architect Austin-Smith:Lord
main contractor ROK
structural engineer TD Bingham (formerly Roy Billington Associates)
M&E engineer AG Hill
quantity surveyor Walfords
main contractor ROK