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Specifier's choice: City University, central London

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Sutherland Lyall looks at Stanton Williams Architects' project to provide a focus for the collection of buildings that constitute a central London university

City University is housed in a campus, more accurately a loosely defined zone of old and newish buildings, just down the road from London's Angel. Last year one of the older buildings was burned out, a special difficulty for the university because it was growing.

Part of this growth included a new social sciences building which will accommodate 1,000 students and staff on a triangular site off the west side of St John Street, one of the three streets running south from the Angel junction. Stanton Williams was commissioned to design the new building on a site which, at the beginning of the last century, had been a chemical depot.

If you count the atrium as a solid, the new building is a parallel grouping of four unequal orthogonal forms running roughly north-south. The two on the east are seven storeys high and are, respectively, a slab of accommodation and the enclosed space of the atrium. The next, longer solid appears to be a storey higher, although this effect is created by a parapet wall around rooftop plant.

The fourth slab is shorter and only four storeys high. With the exception of the glazed atrium, the north elevations of the blocks are made up from big, blank pre-cast concrete panels whose thin, plane-like nature is emphasised by very narrow strips of glazing running up the outside edges of these elevations. These have the effect of detaching the panels visually from the rest of the elevations which are in most cases a lucent, flat surface, an outer skin and, metaphorically, the slippery boundary layers over which the four forms have slid to reach their present configuration. The architect hopes this building will serve as a marker, a kind of gateway to the university quarter - although that supposes that the university as an environment is sufficiently differentiated from the rest of the urban scene into which it is knitted.

Traditional contract The project has a traditional JCT 98 contract with contractor-design portions and bills of quantities. The contract figure was about £12 million. The university has a facilities department that acts as the client. University politics is traditionally a snakepit and the architect has been shielded from this by the facilities department's project manager who deals with the various departments and interested parties in the university. It means, says Stanton Williams' project architect Charles Dymond, 'we get clear instructions from a single spokesperson'.

The university chose the design team and employed it. This kind of arranged marriage can be difficult but, Dymond says: 'We have got a very good set-up with regular meetings and dedicated staff. We are all very familiar with the scheme and its problems so although we go through patches, on the whole it's working well. The main contractor, Norwest Holst, and the university are keen on a partnering approach. Although this is not a partnering contract, everyone is encouraged to work together and be proactive so we can see things coming. The university is cost conscious and everybody is aware of that. So it is not a case of being able to buy your way out of problems. You have to work them out within the budget.' Not surprisingly, the contractor has an important role in this.

There were contractors' design portions built into the contract for such items as the external envelope (though not the roof ), some of the internal glass and those elements which require up-to-date specialist knowledge such as the security system. In working out the general principles of these sections of the contract, the architect called on the expertise of specialist subcontractors.

Like many architects, Dymond has a few reservations about this. In competitive tendering everything is up for grabs and the companies which have helped firm up details of a contract may lose out on getting the work.

Dymond says: 'You do feel you've let them down when they aren't successful at tender stage. But you hope they are wise enough to know about the long-term strategy, that they are always in mind for the other jobs. I have to say that a lot have gone through because they know the project.' It is, of course, normally advantageous for this to happen because there is no need to bring firms which have already worked on a problem up to speed.

Concrete frame The frame, which Lancsville is currently putting up, is reinforced concrete up to sixth-floor level. Above that level the structure is steel, with roof decking around the atrium. The structure is based on a 6m by 9m grid with the external columns set back from the face of the building by a metre.

Around the edge of the atrium, the five columns read more as short sections of narrow walling. The parapet, which adds an apparent floor to the third block, is supported by steel frames fixed into the slab below.

The floors are flat slabs with exposed fairfaced soffits - the same treatment as the atrium walls, which will be painted. Dymond says: 'We have specified plain emulsion but it's something we are looking into a bit more - and we are doing some test patches and will make a decision about what to use.'

Exposed internal concrete is part of the energy strategy. The building deploys its thermal mass, and slightly cooled low-velocity air is driven through chilled beams. At night, the rooftop fans bring air into the building at lower levels to cool the structure.

Unusually, the floor slabs are Lytag lightaggregate concrete. Dymond says: 'Light aggregate is usually applied to Hollorib decking. It hasn't been used as a fairface material since Guys hospital in 1972. But we are using it here as part of the main structural slabs with an exposed face. Obviously we queried the possibility of doing it. Because it's light it has a positive effect on columns, which can be more slender - and the foundations carry a lighter load.'

Skin and glass The external precast concrete panels are left in their off-the-form state, although this is for visual rather than thermal-sink reasons.

They have, however, the structural function of shear walls. This cladding is in the form of half-storey-height panels currently being made by Decomo in Belgium, whence they will be shipped to Clerkenwell.

They are in a blue-ish granite aggregate and will be given an acid-etched finish. The largest panels are 9m wide by 1.8m high.

Dymond says: 'We actually specified a firm which had been a great deal of help. But Norwest Holst had a relationship with Decomo and had worked with them. They gave a very good recommendation and their samples were very good. Norwest Holst was happy and we were happy and Decomo was actually more competitive - even coming from Belgium. And on the unseen west elevation we have Sto render.'

Most east and west sections of elevation are smooth glass rain-screen surfaces from Portal which was the successful sub contractor for the design, supply and installation of the glazing. The open-joint, 3m wide by 900mm high panels are clamped in position and, in the most common condition, have insulation and a spandrel wall behind.

Because there was a need for windows, Dymond's team chose standard Schüco opening windows held in the same plane as the rainscreen panels. There is also a quantity of channel glazing for the very simple strip windows at the outer north corners of the three solid blocks. It is a bespoke design by Pilkington, using fabricated angles with thermal breaks, and is a typical enough way of doing narrow strip windows. The Schüco system could not really accommodate 300mm wide windows. Dymond adds: 'In the specification for the atrium's north building-height solar glass window we gave a choice between Pilkington and a system which only clamps the internal sheet of glass to the supporting structure. In the end we chose Pilkington because they have a thorough track record, the system is of good quality and the practice had used Pilkington before. Their Planar system is so well understood in the industry and there is enough versatility in it to allow tailoring.' This big window is double-glazed Planar glazing, which is fixed to a mild-steel supporting structure spanning horizontally, partly supported by a central stainless steel safety rod attached to the roof.

Glazing within the atrium walls is also by Portal. Dymond says: 'It is structural glazing, laminated and typically set into channels at the base and head. Because it is sometimes the only barrier it has to resist people hurling themselves at the glass. Also, the top two floors are a smoke reservoir so the glazing here has to be smoke- and heatresistant. Happily, toughened laminated glass has the required heat resistance. As part of the fit-out we have specified as much glass in the partitions as possible to allow as much light as possible to get in. And wherever we could do it there are corridors around the atrium edge to encourage this. ' The roof is protected by a Sarnafil membrane. The roof slab is screeded to falls, there is then a vapour check and then the insulation and the membrane. Dymond says: 'We put Sarnafil in the specification. It had been the subject of some discussion because roofs are important and we initially favoured a multi-layer roof which would have self-sealing properties. But on balance, and in discussion with Sarnafil, which provided guarantees, we were sufficiently reassured.'

The atrium has a Siltal rooflight, a system developed in-house by Portal.

Flexible friend Dymond's team has specified plasterboard on standard metal studs for most walls. It prefers metal studding because it is much easier to cut and form on site. There are three types of plasterboard wall, each dictated by the noise-sensitivity of the space and the local use of the building - for example, acoustic labs and teaching rooms. Like the partitioning tender, the door tender is out at the moment: all doors will be timber with hardwood frame and solid core. Fire doors will have vision panels. Although most ceilings are painted exposed concrete, there will be metal suspended ceiling tiles under the roofs on the top floors.

There are raised access floors everywhere:

the energy configuration calls for ductwork in the access floor above, with connections through the floor slab to the chilled beams from Finnish firm Halton. Dymond has specified ASF flooring but expects the main contractor to put forward Atlas as an alternative. The atrium floor is to be an epoxy Armorex floor coating, a liquid applied direct to the screed which is very easily cleaned. There is Dalsouple rubber in areas such as atrium stairs and bridges - and in all the lift lobbies. The passenger lifts will be from Kone and will have a glass back, and the lift shaft has a glass screen so that passengers will be able to look out over the atrium or down Spencer Street.

Architectural metalwork, including balustrades and bridges, is by Bourne Steel, which was selected by the main contractor.

Craig produced the precast stairs and there are Luxcrete pavement lights set into external paving above some of the basement teaching rooms.

The university knows about entrance turnstiles and swipe cards and IT equipment - which of course have to match systems used generally around the university.

Dymond says: 'They know exactly what they want, but for other things such as finishes they generally take our advice - although we have to do presentations. For example we have specified an Escomenda carpet. Still, Norwest Holst may well come up with an alternative. We've also recommended some furniture systems, but furniture is not part of the contract.'

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