Rick Mather's Lincoln School of Architecture, shoehorned into a small site next to a railway track, is a triumph of design ingenuity. We find out how specifiying the right windows made all the difference
The dazzling Lincoln School of Architecture is a bold statement of intent. Designed by Rick Mather Architects, its bulky modernist geometry advertises to prospective students that the University of Lincoln is a dynamic, go-ahead sort of place that is prepared to take risks and, if necessary, put noses out of joint.

Traditionalists may not appreciate the smooth, glacial lines of the five-storey building. It contrasts starkly with the Norman splendour of Lincoln Cathedral, which looms over the new university campus on the other side of Brayford Pool harbour.

Despite the contrasts, Rick Mather's building pays its dues to Lincoln's 11th-century landmark. The building's oblong mass reflects the bulk of the cathedral's great nave and the architect has designed the building to preserve ancient views of the cathedral from the nearby road to Newark. It did so by diagonally slicing off the south-eastern corner of the building.

Design constraints helped to define the building's quirky appearance. Rick Mather Architects also used the building's function to express the external form, which was the simplest way of creating a striking building on the tight £7.9m budget. "The strategy was to express the building's bulk structurally," says project architect Nick Hill. "There's no cost in designing a bold form."

The design criteria had a knock-on effect on the specification of the doors and windows. For the unusual south-facing skewed entrance and atrium, for instance, the architect required large unusually-shaped windows with a high level of solar performance. Another constraint was the railway line on the site's northern boundary, which meant that windows on that side required high standards of acoustic performance.

This limited the amount of natural ventilation the architect could incorporate on the north elevation (see "A building that breathes", page 8).

Despite the constraints, the architect would accept no compromise in the quality of windows. The sharp finish of the buidling's render would have been ruined if cheap windows had been fitted with inappropriate profiles. So to come up with the best solution the architect had to work closely with glazing subcontractor Topside and structural and mechanical engineer Connell Mott MacDonald, which was responsible for the ventilation and building management system.

How the students stay cool

The unusual atrium space is defined by the underbelly of a 150-person lecture theatre. Hill says the wedge shape marks out the entrance. To maintain the clean appearance of the south elevation, Hill wanted to avoid shading the glass using brise soleil. The sloping soffit of the theatre gives some shadow for the east-facing glass, so there wasn't a problem there.

Hill came up with a neat piece of design to create shading for the south-facing glazing. "We set the curtain walling back from the building line, so that the building's mass shaded the atrium," he says. Not only did this preserve the building's clean line, but it also saved money on external shading.

However, high-performance solar glass was still required to prevent the atrium overheating. Connell E E Mott MacDonald advised Rick Mather to specify tinted glazing for the atrium glazing, but the architect was keen to make the entrance area as transparent as possible. It worked with Topside to find alternatives and in the end specified a Saint-Gobain Cool-Lite solar control glass, which achieves a high U-value, reflects heat from the surface and has a high level of light transmission making the glass near-transparent.

The size of the curtain walling in the atrium gave Rick Mather Architects a dilemma. Topside said that for the south elevation, the large 4.2 m high glass panels could only be sourced from Saint-Gobain's factory in Austria. "Nobody in the UK has the capability of toughening or heat-soaking glass more than 3.5 m high," says Steve Prior, Topside's technical director. Prior was keen to reduce the size of as much of the glass as possible because of the long lead times. Topside suggested inserting a transom line in the opening to split the glass into two panels. The reduced size of the lower panel meant it could be supplied from Saint-Gobain's UK site.

The other advantage of this approach was that a simpler, less expensive form of ventilation could be introduced as the top panel of glass could now be made to open. Originally, Rick Mather had been planning to incorporate vents and low energy fans in the soffit above the glass. For Hill, the slight loss of clarity on the facade was compensated by the simpler specification, which also meant any replacement glass in the future could be sourced much more cheaply from the UK.

A stack ventilation system was used in the atrium where air was introduced through the openable curtain wall windows and vented out through the roof lights. The openable windows are controlled electrically by the building management system, devised by Connell Mott MacDonald (see "A building that breathes", page 8).

The 4.5 m panels of glass underneath the sloping soffit on the eastern facade of the atrium were retained in the final specification. "There was no transom, as we wanted to keep the expression of the sloping soffit," says Hill. So these panels did have to be imported by Topside, as did the Schüco frame system used to support the glazing.

Let there be light

Ribbon windows on the south elevation were specified by Rick Mather to give the option of reconfiguring the stud partition offices in future. Wherever the stud walls are positioned, the continuous run of windows will mean there is always a source of external light in each room.

As the ratio of windows to exterior wall is low, Connell Mott MacDonald calculated that high performance solar control glass would not be required. It also drew up the dimensions of the windows for Rick Mather, and calculated how many would need to be manually openable to provide adequate ventilation.

Rick Mather originally specified Valfec frames for the ribbon windows. The specification was for a wood and aluminium composite window, which had a similar profile whether it was openable or fixed – again the architect wanted to keep the facades uncluttered. Project architect Nick Hill was pleased that Velfac came in with the most competitive price, and won the job. "Velfac turned out to be the most competitive as well has having the slimmest frame," he says.

Ribbon Velfac windows were also specified for the top three floors of the north elevation. The railway line meant the third- and fourth-storey windows were not openable and mechanical ventilation had to be used. The top-floor studio was further from the railway, so openable windows could be used. It was cross-ventilated using the ribbon windows and the clerestory windows on the south elevation, also supplied by Velfac.

Quiet in the classroom, please

On the north elevation, Topside was able to improve the specification of the large stairwell windows. "They provided toughened floor-to-ceiling glass for the stairwells, which meant that balustrades were no longer required for the stairs," says Hill. Steve Prior, technical director at Topside, says that the money saved from the balustrades was spent on toughening the glass. To ensure that the glass was able to withstand a person's weight, he designed the frame and glass to BS 6180 and BS 6399, both of which cover live loads on glazing.

The array of windows gives the north elevation a pleasing geometry. On the first floor, where teaching rooms are most susceptible to noise from the railway, the angled facade allows vertical slot windows to be fitted perpendicular to the railway. This means that little noise reaches the rooms, yet students are still offered a glimpse of the city centre.

The quality of Rick Mather's building is sure to attract dozens of applications to the university's architecture course. And Rick Mather has not finished with Lincoln. The firm is responsible for masterplanning the Brayford campus and it has just won the competition to design the performing arts building. If it matches the quality of the School of Architecture, Lincoln will have another building fit to stand in the lee of the ancient cathedral.

A building that breathes

Services engineer Connell Mott MacDonald was responsible for the ventilation strategy at the School of Architecture. The presence of the railway line meant most of the northern elevation had to be sealed, which in turn meant comfort cooling systems and mechanical ventilation had to be specified for the seminar rooms and computer suites. As the southern elevation has no noise constraints, Connell Mott MacDonald was able to recommend natural ventilation to the offices and the atrium.

Connell Mott MacDonald used thermal modelling to work out how much natural ventilation could be incorporated. The model calculated the benefits of solar control glazing, thermal mass and night-time glazing to find the correct size of openable window.

Thermostats in the atrium tell the building management system when window vents need to be opened and closed. On the roof there is a weather station, which measures the strength of the wind. “If you don’t shut the windows in high wind you have problems with draught and noise,” says Connell Mott MacDonald building services engineer Andrew Long. The windows were set to be closed when the wind reached 7 m/s but because of the windy site Long had to change the setting to 12 m/s, otherwise the ventilation would have been inadequate. “We were surprised by how exposed the site was,” says Long.

Staggering achievement: The atrium

The glass screens and rooflights in the atrium throw unexpected patterns of light onto the building’s cleverly designed main staircase. The architect has staggered the positions of each flight of stairs: from the landing the next flight of stairs is positioned one stair width away from the previous flight before carrying on in the same direction.

This cascading stair effect creates a series of sheer walls to the ceiling and at these points there are acrylic dome rooflights. “The position of the openings in the roof to reinforce the rhythm of the cascade,” says Nick Hill. The design also allowed a visual link to be incorporated between the corridors and atrium. The full-height glazed screens from Baydale have a fire rating of 30 minutes.

Recessed slot windows also give an unexpected source of light for the atrium. “The intention was to get a play of light across the atrium and stairs”, says Hill. Rick Mather did not know what patterns would be created and Hill says the striking zig-zag of light was a “happy accident.’ Hill adds that Rick Mather preferred to call them “the work of Mother Nature”.

The corridors echo the clean linear nature of the exterior facade, and this is in part thanks to the way Rick Mather recessed the fire doors into the corridor walls. The doors, which are held open by magnets, are invisible to all but the most inquisitive students.