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Friday18 August 2017

Building Study

Out of the woods: Hopkins’ green learning machine

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Hopkins Architects’ new building for Yale University’s forestry school matches sustainability credentials with a sensitive response to its Connecticut context

Although Michael Hopkins is reluctant to be typecast as such, his practice has built a series of landmark green designs going back to the Inland Revenue Centre (1994) and Jubilee Campus (1999), both in Nottingham. This expertise has landed several academic buildings in the USA. Most recently completed, with Centerbrook Architects & Planners as local executive architect, is Kroon Hall at Yale University in New Haven, Connecticut. It is among the first American buildings to approach carbon neutrality and is expected to receive the US Green Building Council’s top LEED Platinum rating. This has been achieved, with advice from consultant Atelier Ten, by pushing a range of energy-saving measures as far as the budget permitted. The building consumes half the energy of a conventional contemporary equivalent, reducing greenhouse gas emissions by 62%, and generates 26% of its electricity needs from a 100kW rooftop photovoltaic array. All other electricity is purchased from renewable sources.

The university and faculty were both determined that the $33.5 million (£20.7 million), 5,400sq m Kroon Hall be an exemplary sustainable design. Yale is committed to cutting its CO2 emissions by 45% by 2020 and the building consolidates two-thirds of the faculty and functions of the previously dispersed School of Forestry & Environmental Studies (SFES), America’s oldest faculty of this type. The faculty also manages the Yale forests that supplied half the red oak lining the interiors.

Kroon Hall is sustainable in more than technical performance and materials selected. It also provides the setting for an improved quality of life (which “greens” argue offsets the compensatory drive to consume) and brings to what had been a messily disjointed area a sense of integrated wholeness, where no part seems merely residual and uncherished.

With timber-shaded, glazed end walls recessed between stone side walls and below the large vaulted roof, the building might initially seem a mere freestanding length of a mechanically extruded section. It is, yet it also transcends that. The 17m-wide section and east-west alignment of the building permit natural light and ventilation throughout, when Connecticut’s weather extremes allow, and provide the large south-facing roof slope for the photovoltaics. Yet the building also brings a new visual and functional coherence to the area around, Science Hill.

New courts created to the immediate south and, one level up, north introduce the collegiate urban order found elsewhere at Yale, though now planted largely with indigenous species.The court to the south is on the roof of new loading docks which serve Kroon Hall and, via tunnel connections, other nearby buildings. A diagonal path crosses it to the arcade in the building’s south elevation from the previously pointless opening in the neo-gothic building that holds two of its other sides. Even the curved ridge of the dominant roof is supposed to suggest affinity with the swooping roof of Eero Saarinen’s Ingalls Ice Rink (1958) across the street to the west.

At this west end, Kroon Hall is set back from the street, creating an entrance forecourt shared with and uniting the other buildings used by the faculty. On the east and a level up is another entrance opening to a stand of trees, Sachem’s Wood, reinforcing the longitudinal connection made by the arcade. In the circulatory dead end under this entrance is the library. The rest of the lower three floors are cellular spaces, mostly faculty offices, along a central corridor which swells to accommodate the two central stairs. These rise straight towards the natural light flooding down from a central skylight in the roof, a device compelling enough to offset awareness of the height climbed and the relative narrowness of the stairs. Ceiling slabs and columns of in-situ concrete, of which half the aggregate is granulated recycled blast slag, are left exposed so their thermal inertia flattens temperature fluctuations. Other wall surfaces and balustrades are lined in red oak. The external walls are faced in the same Briar Hill sandstone that much of Yale is built from, quarried in Ohio less than 500 miles away — close by American standards. The operable, high performance windows are set deep within pre-cast concrete surrounds and mullions to shade high summer sun from the south, and low east and west sun, while admitting warming winter sun.

The north elevation
Credit: Morley von Sternberg
The north elevation is punctuated by projecting stair towers.

All common spaces form a single suite under the unifying embrace of the vaulted roof. Twenty-one arched frames of laminated Douglas fir support the roof, which is lined in red oak. Along the sides, continuous rows of windows sit on the head of the stone walls and are shaded by the broad projecting gutters above. The gable ends are fully glazed and, except for a strip continuing the side windows, are shaded by fixed external louvres of Douglas fir. The one on the west closes the main lecture theatre and the one on the east the common room, with its view into Sachem’s Wood and beyond. Adjacent to the central stairwells, over which is the photovoltaic-shaded skylight along the ridge of the vault, are smaller lecture rooms and a cafeteria. This is a marvellous suite of spaces, generously lofty yet intimate, warm, relaxed and clubby in feeling, all enlivened by the beautiful quality of light coming from several directions and constantly on the move.

Throughout the building, button-sized red or green lights indicate if conditions outside permit the windows to be opened. Most of the year is either too cold or too hot and humid. Mechanical ventilation then distributes air through under-floor plenums to rise through circular floor grilles and then return via shafts where the stair halls widen to the super-efficient German air-handling plant in the basement. This uses heat pumps to extract energy from ground water, at a constant 14°C and drawn from four wells 457m deep, to heat or cool the incoming air. In winter the water is pressurised to raise its temperature. In summer indirect adiabatic (evaporative) cooling chills the exhaust air, with the coolth transferred via heat exchangers to the incoming air, before the stale air and added humidity is discharged. The same heat exchangers recover winter heat from the exhaust air.

Water for other uses is heated by four panels of evacuated solar tubes set in the south elevation. Water-saving measures include low-flow aerating taps and showers (encouraging bicycle use), dual-flush toilets and waterless urinals. The grey water from basins joins rainwater from the roof in a 91,000 litre underground tank. From here it is released into a pond in the south court where it is filtrated by a variety of aquatic plants, removing nitrogen, phosphates and fine particles. Water is drawn from this pond into another tank in the basement where it is further filtered, disinfected and dyed blue before being used to flush the toilets. Together all these measures save 2.2 million litres of potable water from municipal supplies, 75% of what would otherwise be used. Another 45,000-litre tank in the south court gathers surface storm water to be slowly released without overloading the local sewage system.

Arched frames
Credit: Morley von Sternberg
Twenty-one arched frames of laminated douglas fir support the roof.

Despite the heterogeneity of its output, the buildings by Hopkins Architects are often recognisable as such, and this is the case with Kroon Hall. The architect’s initial reputation was made with steel, glass and tensile fabric, which are still very much part of its repertoire. Yet when context and decorum suggest it, heavy traditional materials are readily embraced and often used in a traditional manner, but always with a modernist rigour and direct expression of structure and construction. Michael Hopkins’ own main regret at Kroon Hall is that the need for super-insulation to deal with Connecticut’s climate led to the firm’s first non-structural use of masonry.

Sometimes the use of traditional materials, or the combination of them and modern techniques, can result in moments that are a tad awkward. Some might see this here in the dominant roof; but such roofs are a New England tradition, found in rural barns and urban structures, such as Connecticut Hall (1753), Yale’s oldest extant building. Any quibble here would be with the long stone faces. Although the fenestration rhythm is broken at the panels of solar tubes, so it is not a mere repetitive extrusion, and the size and shading of the windows is absolutely logical, there is still some of the mechanically repetitive deadness that afflicts so much contemporary architecture. (When will architects read The Old Way of Seeing by Jonathan Hale?).

Other architects might have been tempted to raise the ground-floor ceiling heights, creating a more generously welcoming and wider arcade, and push the rear wall of the now less compressed library outward to admit top lighting from the north court. But the Hopkins team spurned such temptations to concentrate its budget on the splendid top floor which is used year round and after dark. A deservedly apt accolade for the building came unsolicited when a professor, guessing Hopkins director Mike Taylor to be the architect in charge, left his informal meeting in the common room to enthuse warmly about how much the building and its atmosphere enhanced all aspects of academic life within it. The only problem he and others anticipated is that visitors from other faculties are already being attracted to hang out and study there, threatening to overcrowd the building.

Project Team

Design architect: Hopkins Architects
Executive architect: Centerbrook Architects & Planners
Client: Yale University
Structural and M&E engineer: Arup
Sustainable design: Atelier Ten
Landscape Architect: Olin Partnership
Civil engineering and stormwater management: Nitsch Engineering
Geothermal engineer: Haley 7 Aldrich
Facade engineering: Simpson Gumpertz & Heger
Thermal performance: Waltham
Materials handling: SEA Consultants
Code consultant: PR Sherman
Specifications consultant: Kalin Associates
Elevator consultant: VDA
Cost estimator: Faithful & Gould
Construction manager: Turner Construction Co

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Readers' comments (3)

  • Stunning ... the topmost space appears magical ...

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  • Arrested my eye - and held my attention with a lift in my spirit as I read on. 21st century gravitas and grandeur to envy.

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  • A seriously important template for designing libraries and our schools - and not just those buildings required by the temples of academe. Note the comment at the end of the article from a professor who left his meeting to speak with Mike Taylor. Ultimate accolade that. No award could better it.

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