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Sutherland Lyall speaks to Emma McLaren of van Heyningen and Haward Architects about developing a new conference centre for a site on a showground in Suffolk.

The 100ha Suffolk show grounds at Ipswich are packed with cars and marquees and cattle and sheep pens. But only for two days a year. The rest of the time it is just a big green space which looks a bit like a racecourse between seasons. The owner, Suffolk Agricultural Association, occupies one of the few permanent buildings, the Trinity Rooms, a shed-like structure with what looks like a 1930s suburban villa stretched across on the front. Apart from the annual show, the association is quite an active institution among local schools, colleges and the farming community.

Conscious of the underused site's potential, it decided to start thinking about its year-round use. What the association decided it needed was a new IT-equipped conference centre. It carried out a masterplanning study which identified the best site as being adjacent to the Trinity Rooms which, like it, would face north to the access road, with a 24m-wide garden between the two.

Following a 2003 pitch against several other practices, van Heyningen and Haward, which had designed the nearby Sutton Hoo visitor centre, was selected as architect and started work with a team of consultants with which it had worked a lot before.

Project architect Emma McLaren says: 'Initially the building was going to be one big hall. But the client gradually developed the idea of exible spaces.' A consequence of that was the need to be able to control noise between whatever spaces were set up at any one time, and Arup Acoustics was drafted in to advise.

Unexpectedly, noise leakage from the building became an issue for local people on this open site: even though the nearest house was 1km away, planning permission was conditional on the building's skin being acoustically opaque. This, McLaren says, 'had consequences on the services. Our desire was to have a naturally ventilated building, so redesigning it so it could be totally sealed increased the budget. It can still be ventilated naturally'.

The new building is a big 26 x 46m-long timber-clad shed with a pitched standing-seam zinc roof and several bands of skylights on each pitch. The roof overhangs 7m at the front, supported by braced timber columns. Inside at the front is a lobby with a bar and men's lavatory to the left and the women's lavatory to the right. Straight ahead, double doors lead into the big space at whose far end are the kitchen and catering and furniture stores.

This big space can be divided into a maximum of three function rooms down the east side of a top-lit corridor, and four (two and two half) rooms down the west. Many changes can be rung on this basic arrangement. There is light everywhere: the front gable is curtain walling, the side walls are largely composed of glass windows and doors, and the skylights bring light right into the centre of the 26m-wide space.

The association wanted a big space - even after deciding to incorporate its exible division into rooms. And it wanted sustainable materials which meant, as far as possible, timber.

Consequences were both acoustic and structural. To achieve quite such large unsupported spans, the structural engineer, Price and Myers, designed a big spine truss - actually two lattice trusses overhead, either side of the spine corridor zone. In section these are inverted triangles, and the two visible faces of each are clad in timber slatting. From these steel spine trusses, by TSI Steel, long-span glulam rafter beams from Lilleheden glulams span to the walls, where they are supported on steel columns. Where there is a movable partition there is a 0.5m-deep horizontal beam directly below the relevant rafter, stiff enough to support the 12m folding panels of the 10 x 4m Alco Beldan NW100 movable acoustic wall system. The leaves fold into tall cupboards along the side walls and are free standing at each end of the corridor zone.

The decision to go for exible spaces and the consequent need for acoustic separation means there is a lot of extra kit, including ducting and air-handling units, for the seven possible rooms. This has been routed to the firstfloor plant rooms at each end of the building through the middle of each of the two spine trusses, and is accessed using mini scissor lifts. Acoustic separation between compartments is achieved by filling in the triangular space between the rafter and the horizontal beam carrying the wall panels with 15mm panels of glass.

The building pays deliberate homage to the Suffolk agricultural vernacular, with timber construction and cladding.

The architect points out that the other virtue of timber is that is has low embodied energy - something the sustainability-savvy client wanted. And, by using real timber for the visible structure and cladding the interior and much of the exterior with timber, integrity of structure and materials is more or less maintained.

The only time there is a bit of fakery is in the long slender columns at the front supporting the deep roof overhang which are itched: timber either side of structural steel plate.

CONTRACT The deadline was less than a year away from the last annual show and, McLaren says: 'For reasons of time the client was keen to get the contractor on board as soon as possible.' That meant a twostage JCT98 contract without quantities. McLaren continues: 'Davis Langdon & Everest developed a cost plan as we were developing the scheme and, meantime, with the client we selected the contractor [Essex firm Hutton Construction] on the basis of overheads and prelims - and on its general approach. We selected the company we thought we all could work with. It worked very well. It was important for this building to take only 34 weeks, so we started on site before all the drawings were complete.

'When we appointed Hutton we worked with them to develop the second-stage tender and negotiated and they came up with their price. The quantity surveyor had to be quite up to date.

And there had to be good communications between the QS and builder. We did it not to cut costs but to build a relationship and get on site as soon as possible. There are pros and cons with twostage contracts but everybody was anxious to make it a success.

There were some difficulties with the services when the flexible strategy became fully evolved but it was a team effort and we got it solved.'

McLaren says: 'The spec was NBS, the paper version - we used MicroStation v8 for drawings but the contractor, Hutton, is quite small, so there were no computers on site.'

BLOCKING IT IN The need for the building to be acoustically opaque had an effect on the insulation specification. McLaren says: 'The wall insulation was quite interesting. We used Rockwool Flexi and it was ideal because it has a density. We wanted to use Warmcel newspaper but it has no density. The other reason was that to use Warmcel you blow it in the walls. Where there are timber studs and with horizontal nogging, the contractor would have had to drill lots of quite big holes. When you do that you also drill through the vapour barrier. It was something which was going to take quite a long time and at Ipswich the decision was made on site to use the Rockwool. It wasn't a cost reason, rather time.'

For underfloor insulation, McLaren specified rigid Kingspan Styrozone H350, which was laid on top of the concrete slab. Then the heating pipes were laid out and the screed poured.

Roof thermal insulation, Rockwool Roll, sits between the purlins.

Although it has good acoustic characteristics, Arup Acoustics also recommended a 50mm layers of Lamaphon black-faced acoustic insulation from Siderise laid on top of the slatted timber ceiling.

WINTER SKIN The roof above is of 500mm-wide Rheinzink standing-seam zinc trays. McLaren says: 'Zinc is environmentally sound and really does maintain its appearance, which was important because this building is rather exposed. The builders had so much space on the showgrounds for their compound - it was probably a dream site.

They started putting it on around November when it could be cold. Often builders have to make all the trays on the roof. Here they were able to do most of it in an adjacent sheep shed and then they lifted the trays on to the roof and finished off the seams.

So it took a relatively short time to put on the roof.'

For the external walls McLaren specified larch heartwood.

She says: 'We had used it before. During product research we discovered that larch heartwood doesn't need preservative. The client wanted a consistent finish over the whole building. We have found with timber buildings exposed on all four sides that you can get shadow staining. So what we did was paint it a warm grey - not a stain but paint. It had been kiln-treated with a fire retardant and then painted with one coat of primer and one finish coat and stored for the winter in the sheep shed. Then it was nailed on and given the final coat.'

McLaren adds: 'We really like using timber boarding on internal public areas. It's robust and has high durability. And we followed up the same material with hit-and-miss boarding to the ceiling to allow the acoustic insulation to do its job and to clad both sides of the spine trusses.

'Inside we use European redwood with one coat of light white paint so that you can still see the timber and the grain - and then two coats of varnish to give a lightness.'

Another element which changed during the contract was the rooights. McLaren says: 'The initial concept was a metalframe lantern right down the middle of the building. We were looking for a cost-effective way to do this and we went back to the Velux rooight operated by electronic controls. We now have 38 of them running down in two lines either side of the ridge, lighting the corridor zone, and another row below that on either roof pitch lighting the rooms below. The detail round them is very simple. ' At ground level McLaren looked at timber glazing. She says: 'The client wanted to have big openings so people could walk out of the sides of the building into the garden. And on the east and west elevations we had to have a fire escape from every room.

And anyway we wanted very big doors so as to maintain the sightlines to the garden outside - which meant they would be 3m high all the way along with a large window above that as well.

We specified Sch³co swing and sliding aluminium frame doors with slender frames. We have used Sch³co before and have used its FW 50+ sections for the curtain walling in the entrance wall.'

UNDERFOOT In choosing the carpet, McLaren says: 'We thought that if the building were used fully the carpet would have to disguise any previous use. So it's a felt-backed patterned carpet which we designed and Weston Hammer wove. It is a roll carpet rather than carpet tiles because the client reckoned it looked to replace carpet every four years. The client is very aware of what it takes to run a building of this size and it employs a good team.' There is heavyduty non-slip vinyl in the 400-meal capacity kitchen - as required by the regs - and in staff areas Marmoleum lino from Forbo Nairn. The entrance and adjacent lavatories have Domus Dolomiti D1D09 oor tiles with a CT001 low-profile entrance matting with aluminium strips built in.

QUALITY ASSURANCE McLaren concludes: 'We believe that we specified high-quality but simple products and the client went with quality because it is to have a long lifetime and had to cope with a lot of people using it. For example, we got Forestry Stewardship Council assurance for the glulam beams, even though they were sourced in Scandinavia.

The Armitage Venesta preplumbed panel system Sanit was quite expensive. The contractor believed that you could make up the same with standard items for less money. But the client insisted it wanted the fittings to be robust and have the level of finish of Venesta. On the other hand the contractor went with our choice of ironmongers, Allgood, which we have used many times before.

And in the value engineering the cut-back was mostly on services.

Everyone realised that each choice was made for a particular reason. They realised we couldn't cut corners and the client didn't want to.'

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