With its design for an undulating geodesic dome roof, London-based Wilkinson Eyre Architects
turned an underutilized infill space into the social and academic heart
of the University of Exeter’s Streatham Campus. The 37,674-square-foot,
free-form, timber grid shell—one of the largest in the United
Kingdom—covers a 96,875-square-foot area called the Forum, which ties
together the Great Hall Piazza, student guild, library, and other
academic facilities with cafés, a shop, and a bank along a galleried
“high street.” The soaring ceiling of oak-clad spruce timber shelters
the Forum from South West England’s wet climate and floods it with
natural light, thanks to a mix of glass and ETFE (ethylene
tetrafluoroethylene) panels.
Wilkinson
Eyre director and project lead designer Stafford Critchlow and his team
used wood for the roof to reference the tree-covered campus, which was
once part of Reed Hall, a Victorian-era country house and botanical
garden. A pure timber grid shell of woven wood would have taken too long
to build. Working with engineering firm Buro Happold and subcontractor
SH Structures, Wilkinson Eyre developed a hybrid grid of timber linked
by custom-fabricated steel nodes and flitch plates. The project's
success is clear: The iconic ceiling now appears on T-shirts, wayfinding
signs, and event posters. “They used the grid-shell structure as a
graphic, a kind of totem,” Critchlow says. “It’s become this sub-brand
within the university.”
Hufton + Crow
The Forum’s freeflowing gridshell mirrors
the rolling hills around the University of Exeter. The designers used
European oak to create the effect of a wooded canopy and capped the roof
in copper, which will oxidize, form a green patina over time, and allow
the building to age in harmony with its surroundings.
Hufton + Crow
Natural light pours in through triangular
bays filled with EFTE rooflights by London-based Vector Foiltec, chosen
because they are lighter than conventional double glazing. Each 48
square feet EFTE light consists of a three-layer cushion with a random
printed frit pattern. Double-glazed windows cover the triangular
openings in teaching and study areas to reduce rain noise.
“We originally envisioned more glass, but we ended up with half the
number of light bays based on daylight modeling,” Critchlow says. “You
can have too much light, especially when students are working on
computers.”
Hufton + Crow
Weathered, green-oak slats give the sun
screen along the outer rim a feathery, natural look. The slats tie in to
steel T-sections welded onto a 7.5-inch-diameter perimeter tube.
Hufton + Crow
The team needed to stiffen the
gridshell—to keep it from collapsing upon itself—without stretching
tension ties across the ends. “We wanted a delicate junction where the
roof oversails the adjacent parapet walls,” Critchlow says. “It’s all
about making the shell structure as delicate as possible.” The team
propped the gridshell up with tubular steel pylon columns that anchored
into the ground.
The gridshell consists of prefabricated
glulam timbers (twin-flitched spruce members doweled and secured with
pairing screws) linked by round galvanized-steel nodes. Each node is 5
inches in diameter and contains six mounting plates for receiving six
timbers, which radiate out from the nodes like stout wagon spokes. When
linked together, the timbers form large triangular bays, which are
subdivided by smaller beams. To realize the complex geometry of the
undulating dome in wood, the team used standard timber sizes (17.75
inches by 3.5 inches) and custom-fabricated steel nodes bristling with
mounting plates cocked at different angles to receive the timbers. The
designers modeled the system using Tekla and Autodesk software. The
nodes, timbers, and other parts were assembled on site like a
complicated “piece of flat-pack furniture,” Critchlow says. A plywood
skin and standing-seam copper cover the roof. Beneath the plywood, the
ceiling comprises rigid thermal insulation, acoustical insulation, black
acoustically transparent fabric, and finally the finished surface of
0.75-inch-by-1.73-inch kiln-dried oak slats spaced 1.73 inches on
center.
Freelance
journalist Logan Ward has written about architecture, design, and innovation
for The Atlantic, Smithsonian, Garden & Gun, Preservation, Popular
Mechanics, and many other magazines. Ward is the author of See You in a
Hundred Years, the true account of the year his family traded digital-age
technology for the tools of his great-grandparents’ era.