Onsite

‘A' level in woodwork

14 September 2010

Meeting rooms sit under a flat roof while the main studio is roofed in a lattice of timber and glazing ©Niall McLaughlin

A new building for a diverse range of students at Cranfield University puts timber at the junction of science and art. Michael Willoughby reports.

Not all architectural statements have to be loud. At just a single storey, the newly-completed Centre for Competitive Creative Design (C4D) at Cranfield University, Bedfordshire, demonstrates the precision, geometrical intricacy and feeling of lightness that can be achieved using contemporary timber construction. With its roof structure tilted up to the skies, 

the pavilion looks as if it’s about to lift off and join the light aircraft parked at the neighbouring airfield.

The 330m2 building was commissioned to bring together Cranfield’s business and science students with those studying design courses at the University of the Arts London. Cranfield, which offers post-graduate, masters and PhD courses in business, health, science and technology, wanted to mark this collaboration with creative types by commissioning a stand-out space in which it could help these different people work together.

“We wanted to make a statement in terms of what is going on,” says Malcolm Grant, industry services manager for C4D. “[The building] shows the intent of how seriously we take the subject and how far forward we are looking to move that.”

Designed by Niall McLaughlin Architects and built by contractor Kier Marriott, the timber pavilion centres on a 175m2 main design studio where students will model their ideas in the digital and real worlds. Alternatively, the space can be reconfigured to hold exhibitions, or act as a conference and training space. It is dominated by full-height glazing along one elevation, creating uninterrupted views onto the neighbouring airfield.

Opposite this window-wall, the studio is edged by meeting rooms. Offices and the washroom then line one side, while the building’s entrance and storage facilities form the fourth elevation.

The building sits on a deep-filled trench foundation, above which structural engineer Price & Myers had to design two different types of slab: one end of the building sits on a ground-bearing slab, the other on a “suspended slab” on top of compressible materials — a design that allows for potential heave from the roots of a nearby sycamore tree.

The structural box is made using KLH laminated timber wall panels. This product was chosen because of its sustainability credentials, the ease with which it can be pre-cut to size in the factory, and the straightforward assembly on site — the panels are fixed together with steel brackets and timber screws.

The KLH is exposed internally and finished with a translucent white stain. Where required for acoustic reasons, Rockwool insulation is sandwiched between two panels to form partition walls. To external walls the insulation sits outside the KLH structure and the building is clad with a larch rainscreen.

This timber box is then topped with two 100mm thick glulam beams that run the length of the building, and supported by three concealed steel supports. To support the complex roof above, these primary beams are combined with 14 secondary beams that span the breadth of the building.

From the contractor’s point of view, the roof represented an extremely tricky 3D puzzle. Essentially, the lid of the timber box has been rotated to sit at 45 degrees to the main structure, and corrugated into a series of timber slopes above ribbon glazing to maximise the amount of north light entering the building.

The north light roof structure comprises a series of tilted KLH panels, most of them  long rectangles, combined with a few triangular panels at the corners. These are attached to the 14 secondary glulam beams, supported at their lower edge on wooden wedges and at the higher end on steel supports.

The “tilt” between the lower and higher panel edges is glazed with a triangular window on the slanted sides (sitting parallel to the elevations) and with ribbon windows on the longer sides which run from corner to corner across the main space. To seal the box, the slots between the secondary beams are also glazed.

Site manager Brian Reece, from Kier Marriott, says that putting the roof together was a huge challenge for the construction team. With a tight 36-week contract (which also included demolition of the existing building and repositioning an emergency access road) there was no chance to take site measurements and the KLH and glazing elements had to be fabricated off-site
at the same time.

“Working with KLH is meant to be like Meccano,” Reece says. “But though you can manufacture elements to tight tolerances it’s difficult for us to erect to those same millimetre measures.” In fact, the two weeks for installation of the roof allowed for in the construction programme was extended by a week to ensure everything fitted together perfectly.

The key issues for the team were ensuring that the steel rods that support the roof panels at their highest edges were correctly aligned with the predrilled holes in the secondary timber beams, that the wooden wedges that take them at the lowest edge fitted properly, and that the openings for the glazing were of the correct size and alignment.

 

Foster's Cranfield library is adjacent ©Niall McLaughlin

There was no margin for error built into this glazing, so installation was particularly tricky with an arrangement of two triangular glazed panels surrounding ribbon panels which has to be properly aligned on three sides. To cap it all, because the roof panels are sloping and at an angle, the external glazing opening is a different size from the internal. “That was the criticality — trying to make sure that we provided the correct opening sizes for the glazing,” says Reece.

Situating the building next to an airfield may be a treat for designer eyes, but there was a danger of offending their ears if traditional ventilation methods had been used. So a sealed, acoustically isolating glazing system was chosen with ventilation provided via a raised floor containing a plenum through which air is pulled into the building.

From a sustainability perspective, the building would likely be awarded a B-grade Energy Performance Certificate, according to Reece. This is because it is linked to the university’s carbon-heavy district heating system, which is currently being upgraded. On the other hand, Kier Marriott has achieved an impressive level of air-tightness — just 3.7 air changes per hour, compared to the design team’s target of seven.

To maintain the purity of the interior space, the roof has been designed to hide the electrical and fire alarm cabling. Cables are carried over the flat roofs on the meeting rooms in cableways routed into the KLH in the factory — a measure that required extensive pre-design. The north light structure is, in fact, laced with flexes, although these have been artfully hidden and fed though 80mm downpipes at the corners.

From the downpipe, the cables travel through the primary beams and panels so that everything is invisibly linked. The arrangement has allowed for suspended aluminium lighting frames, a washroom lit by neat, recessed lamps, and for smoke alarms to be attached directly to the main roof.

Standing in the studio space, from some angles, the roof panels almost disappear and the pavilion seems open to the sky. With such an ingenious design to work in, C4D should provide exactly the right combination of technical ingenuity and creative flair to inspire a new generation of product designers. 

 

The roof comprises a series of KLH panels that are attached to 14 seconday glulam beams ©Niall McLaughlin

©Niall McLaughlin

Modelling all the angles

To help with the process of fabricating and assembling the complex roof, KLH created a computer model from which the architects were able to extrapolate dimensions and cross-check fabrication drawings for glazing and roof flashings. Meanwhile, a physical model was built to help those working on the project to figure out how it fitted together more easily than two dimensional drawings could have.

“The computer model was a help in working out the dimensions, while the physical model gave us a great insight into how it all fitted together,” recalls Brian Reece.

Although the roof may seem to be an architectural flight of fancy, Niall McLaughlin points out how much of a practical solution it represents. North light has been the task illumination of choice everyone from artists to motor mechanics, he says. “[Allowing as much daylight in as possible in minimises] the daytime lighting load on the building because every part is well lit. We have created a bright airy space for students which is also good for computers because you get very little glare.”

And as the cantilevering of the roof takes the structure beyond the boundary of the building, it shelters the vertical glazing to reduce solar gain, thereby mitigating the need for cooling — potentially a major factor in what is essentially a glass and timber box.

 

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