When Arup Associates traded in glulam beams for steel trusses at the University of Cambridge Sports Centre, a complex set of design problems simply disappeared, writes Felix Mara. Photography by Simon Kennedy
Some architectural projects have Eureka moments, when changing one parameter instantly unravels a Gordian knot of design problems. The University of Cambridge Sports Centre, designed by integrated practice Arup Associates and ready for action in July this year, was such a project.
As a voluminous shed, the sports centre looks simple enough, although spanning 36m with what is essentially a dome, and providing for multiple functions with a degree of flexibility, isn’t something you can do with your eyes closed. First you must address the essential requirements of the various sports which are to be accommodated, ensuring that heights, areas, atmospheric conditions, comfort standards and other details comply with Sport England guidelines, as well as additional client requirements. At Cambridge, Arup Associates was asked to provide a 34 x 37m eight-court sports hall with tiered seating for 400 and facilities for weight training, squash, rugby and Eton fives and also badminton, which requires specific atmospheric conditions, as well as multipurpose and ancillary accommodation. Acoustic performance was also a priority, in spaces where activities could generate a lot of clatter and may double up as written examination venues. And, of course, the performance of the timber-surfaced semi-sprung sports floor was crucial.
Then there were the stipulations, also strict, set by the local authority planning department. The sports centre - phase one of three designed by Arup Associates, with indoor and outdoor tennis courts and a swimming pool completing the complex - is part of the West Cambridge masterplan. On the edge of the green belt, the complex adjoins growing academic and student residence buildings, all in a rural setting. Whereas many of the sport activities are subject to minimum, as well as plus-or-minus zero, height requirements, the planners were concerned with maxima. There were also renewable energy targets and restrictions on the cost, which came in at £1,500 per square metre.
Finally, there were a number of further objectives, including natural ventilation and daylight where possible, which of course cuts energy consumption, as well as Arup Associates’ additional architectural aspirations.
Arup Associates won the competition for the entire sports complex back in 1999, but funding only became available in 2011. The intermediate design had an appealing array of glulam beams spanning north to south across the main sports hall, and these married up with a colonnade of timber fins on the entrance facade, where their function was primarily architectural, as it faces north and so does not need to regulate solar gain or glare. The colonnade has been built, chosen for its academic connotations and intended to be replicated on phases two and three. But in an astute design move, Arup Associates jettisoned the glulam beams, whose depth would have increased the height of the roof because the soffit levels were fixed. In their place, there are steel trusses spanning 36m and cantilevering at either end to pick up the walls. Because these run east to west rather than north to south and are perforated, they coincide with glazed gills in the roof which admit daylight and have horizontally pivoting double-glazed louvres providing natural ventilation.
As well as killing the four birds of height, natural ventilation, daylight and structural efficiency with one stone, Arup Associates’ roof design addresses the complex acoustic requirements of the sports hall. The client and users wanted minimum acoustic absorption on the walls at low level, where activity is concentrated. Although there is 300m² of perforated MDF acoustic panelling on the internal walls, Arup Associates maximised the sound absorption of the roof, which has acoustic absorption in the troughs of its perforated deck.
The natural ventilation strategy works in various modes. In mid-season at midday the glass louvres, operated by external electro-mechanical actuators, are open and the low-level ventilation ducts are closed, so fresh air circulates in the hall, drawn in through the gills from which it also escapes.
On winter mornings, these louvres are closed to reduce heat loss and the hall is mechanically ventilated, heated by radiant panels suspended from the roof. In peak summer conditions at midday, fresh air is drawn in through visually suppressed low-level natural vents and escapes through the louvred gills.
However, for mid-summer badminton events, to minimise interference to the flight of the shuttlecock, the high-level louvres are closed and there is full natural ventilation purge using low-level ducts.
The gills also support 200 photovoltaic cells clipped to the seams of the zinc roof. These cells provide renewable energy for the centre’s comparatively modest demands, which are made possible by its use of natural ventilation and daylight. There are also solar thermal hot-water collectors above the skylight. A doughnut ring of perimeter plan bracing resists the thrusts of the roof’s arch action, and access is provided by a latchway system integrated with gutters which form valleys and run along the perimeter, where they are concealed.
The success of the University of Cambridge Sports Centre relies on a roof which works hard and cleverly integrates its multiple functions: the outcome of collaboration between the Arup Associates disciplines involved, and some hard thinking about the actual benefits of glulam roof beams.