Species: American red oak
Architect: Hopkins Architects
Photography: Morley von Sternberg

When Hopkins Architects was interviewed about designing the new building for Yale’s School of Forestry & Environmental Studies, project director Mike Taylor and Sir Michael Hopkins took the opportunity to have a look at the university’s plans room. Their main aim was to see the drawings for such important buildings as Louis Kahn’s art gallery, but while they were there they made a discovery that had a vital effect on their design.

‘We saw that Yale had its own forests in New England,’ Taylor explained. ‘We thought then that it could be a masonry building with a timber lining – and that it could use their own timber’. The result is a building where much of the internal excitement comes from the use of American red oak, on stairs and liningswalls, drawing you up to the most dramatic space on the top floor, and imparting a warmth to the building that might otherwise have been lacking. 

The building, known as Kroon Hall, occupies a space that was previously a messy backyard. ‘All the good sites have gone now,’ said Taylor, but this positioning on what could fairly be described as a brownfield site accords with the aspirations of the building, which were to be as environmentally friendly as possible. The client wanted the building to score LEED platinum, the highest category in the US system (roughly equivalent to BREEAM). But it wanted to go further, to be carbon neutral.

Hopkins designed a building that is one of the greenest in the US, using many approaches that are common in the UK, but unusual in the more extreme climate of New Haven Connecticut, which has hot humid summers and cold winters. Only in the pleasant ‘shoulder seasons’ of spring and autumn is it feasible to rely entirely on natural ventilation.

Its approach is one of orientation, high thermal mass and good insulation, to minimise the demand for energy. There is as much natural light as possible, and an exposed southern façade to allow solar gain in winter, but with shading to keep out the high summer sun. Having kept the energy requirement as low as possible, the building then has windows that can open in spring and autumn (there is a system of red and green indicators to show when it is appropriate to do so). The rest of the time the building uses displacement ventilation with heat recovery.

Heating and cooling come from heat exchange with geothermal wells that are nearly 500m deep. And there are photovoltaic panels on the roof to provide another source of renewable energy.

If all this sounds complex, the building itself is surprisingly simple, a single, barrel-vaulted structure, two storeys high on one side, and three on the other to accommodate a change in level on the site and provide access beneath for service vehicles. It is also a clever piece of placemaking, creating new courtyards on either side of it.

It is initially surprising that the most public spaces are on the top floor, with relatively routine cellular offices below. At the top are an environment centre, classrooms and gathering spaces including a canteen. This was a deliberate attempt to create a new heart for the school, to complement the informal gatherings that can happen outside when the weather allows. Because of the form of the building, the top floor is the most dramatic space, and so most suited to this use.

The centrally placed staircase draws people up to this space, and, especially on the ground floor, its warm patina contrasts enticingly with the cooler exposed concrete finishes. The timber used is American red oak, which comes from the Yale Tourney forest, the largest of the seven forests that were donated to the university in the 20th Century. In the very northeast of Connecticut , it covers 3.213ha, and is FSC certified. It mostly consists of mixed hardwoods with small stands of pine.

The timber that Hopkins chose to use was red oak, and in the end about half of it came from Yale Tourney and the rest from elsewhere, although it was all FSC certified. It was used for all the internal timber, with the exception of the glulam beams, which are of Douglas fir, as is the external timber shading. American red oak is not suited for external use in so harsh a climate, and the glulam manufacturer also has specifications that exclude its use.

For Hopkins this is the first time it has worked with American red oak. It has extensive experience of white oak, particularly at the parliamentary building Portcullis House, and also at Haberdashers’ Hall in the City of London. ‘We were a bit guarded,’ said Taylor. ‘It is more characterful than white oak. There is more variation and more warmth. We were concerned that it could look like exaggerated variation.’

When working with timber in the UK, Hopkins’s normal habit is to create panels and then to hang these directly, but at Yale it went with a more American process of using ‘v-line’ boarding – roughly equivalent to tongue and groove. ‘You start at one end and move along explained Taylor, explaining that this was a cheaper solution, although he did not think it would have been in the UK. ‘It’s a local thing,’ he said. ‘I imagine if you did it in the UK it wouldn’t look the same.’

Hopkins was in the fortunate position of being able to select the timber, which was all kiln-dried. Before specialist local timber contractor Legere Group started installing the boards, Hopkins set up a selection specification, ensuring that any boards in which the variation was too extreme, or where there were too many knots, would be rejected. The contractor then installed them, deliberately randomising them so that, although the variation is not extreme, it is most definitely there. On the upper floor, where this panelling forms enclosures to some teaching spaces that go up to meet the ceiling, there are three rows of vertical planking at the ends, and an alternation between horizontal and vertical planking on the main entrance walls, with the horizontal element acting almost like a portico.

As well as the panelling there are other elements that use red oak. The stairs have oak treads, with non-slip strips set into them, contrasting with the exposed concrete of the risers. An informal space at the end of the top floor has red oak flooring, made into panels each of which is the size of four of the raised floor panels, so that it can be lifted off and the services can be accessed. With dark leather sofas, and the timber panelled walls of some enclosed classrooms behind, the effect is a little like being in a modern, and determinedly non-exclusive, version of a gentleman’s club. The use of red oak for some low-level tables adds to the harmonious impression. There is other red oak furniture in the building as well, in particular  some benches near the entrance, although none of the timber for this furniture was sourced from the Yale forest.

But after the panelling, the most obvious place where red oak has been used is on the ceiling panels to the vault that runs the length of the building. These panels, made by Rulon Company, are of solid formaldehyde-free MDF and contain apertures for lighting and sprinklers, as well as having openings to an acoustic backing. They are veneered with red oak, and have solid red oak edges to them.

Initially Taylor was concerned about the visual contrast between the red oak panelling and veneers and the Douglas fir glulam beams, but the effect is harmonious. And the use of locally grown oak, even if there was not enough of it to do the whole job (the forests are mostly maintained as a research resource rather than for commercial exploitation) is in keeping with the approach on the rest of the building. Externally, it is clad in Briar Hill Stone, a pale yellow stone that has been used widely on buildings on the campus, so that Kroon Hall sits comfortably with its neighbours.

What is most striking about this building is the way that almost every decision about its design was informed by an environmental agenda, and yet it is an eminently strong and rational piece of architecture that doesn’t proclaim its environmental credentials, except to the cognoscenti.
The architect describes it as ‘a modernist blend of cathedral nave and Connecticut barn’. It is orientated east west, with the long northern side, with its minimal openings, set into the hillside, and a much more open southern side spilling out into a garden.

The concrete structure, exposed internally to provide thermal mass, has 50 per cent of the cement replaced by blast-furnace slag, a waste material. Low-velocity fans in the basement circulate the air in the displacement system.
It is easy to concentrate entirely on energy when one thinks about environmental performance, but water is also a valuable resource, and the architect has not neglected this in its design. There is a rainwater harvesting system that not only gathers water from the roof but also uses the garden in the south courtyard to help clean it up. The rainwater is directed to an area of aquatic plants which filter out sediment and contaminants. From there it goes to underground storage tanks, and it is used for flushing lavatories. The saving in water, the school of forestry estimates, is a staggering 500,000 gallons a year.
The architect even thought about the lift (sorry, elevator), in environmental terms. It has specified a counterweighted roped holeless hydraulic elevator, which uses less energy than either an ordinary hydraulic elevator or a typical roped counterweighted elevator. Equally importantly, by placing the staircase at the heart of the building, it has helped to ensure that only those who really need an elevator will use it.

On completion of the building in April 2009, Richard C Levin, the president of Yale, praised it as ‘Yale’s most sustainable building to date’ and said that he hoped ‘its energy-saving concepts will be emulated widely and inspire others to advance green building design even further.’ Set anywhere, this building would be an achievement in both architectural and sustainability terms. The fact that it has also replaced an eyesore of a power plant and created a focus for a department that previously inhabited a soulless hotchpotch of buildings is a bonus. And for the students and faculty, what could be better than to be reminded of the subject of their study every time they look at those red oak walls?  With busy agendas they are unlikely to get to the forest as often as they might wish. How marvellous then that the forest has come to them.

by Ruth Slavid