|
THE
PISHWANTON HAND-BUILT GRIDSHELL
Both
the Flimwell Modular gridshell and the large scale Weald and Downland
building have required large amounts of public money into them.
It could be it is fortuitous chance that Sussex is the epicentre
of the current British gridshell phenomenon. There is, however,
a third building, completed in 2002, which is a gridshell, but
it has been built on much smaller budgets, done independently
and through the energy and enthusiasm of a small group of people.
 
Image
David Tasker
The
building is the craft centre at the Life Science Centre Trust,
Pishwanton, East Lothian, a centre devoted to the renewal of the
largely unknown Goethian approach to scientific research. Designed
by the respected architect, Christopher Day, it is deeply organic,
quasi-rustic building. It mention of the core of the building
- the craft room, where ears have been perking up, for its roof
is a ten metre span self-built gridshell, constructed overwhelmingly
by the craftsmanship of working hands. The £1.8 million
it cost to build Weald and Downland, is beyond the reach of many
communities who might want to explore such forms at an equally
valid, if far smaller scale. This is where the Pishwanton building
comes in. Through what appears to be a mixture of fortitude, foolhardiness
and staying power, the Pishwanton building has been completed
over four years in a stop-start, almost hand-to-mouth fashion.
It is testimony to those involved that against the kinds of odds
where more mainstream professional operations would have despaired,
the Life Science Trust has seen the project to completion. And
they have done so at a cost which is a fraction of the institutional
amounts needed: £50 and £60, 000 .
Christopher
Day began sketching out the architectural ideas in 1997. The first
work commenced in 1998, the buildings function being to provide
both sheltered facilities for Life Science Trust activities in
bad weather, and for pottery classes, wood carving and other woodland
crafts. The original engineer’s envisaged an apparently
sophisticated but prohibitively expensive truss system, which
would apply beams and columns to the central area. It was at this
point that David Tasker, a structural engineer, who had already
been involved in the construction was brought in to reassess the
situation; and Tasker, upon seeing the column planned, thought
“this wants to be a gridshell.” The resulting plan
envisaged three pod-like gridshells resting on an irregular hexagon,
nine metres in diameter. Today, on each side of the completed
hexagon room are two wings, one for storage the other comprised
of two smaller rooms.
 
Image
David Tasker
Tasker
describes the next steps as working through limited structural
analysis, "backyard engineering", mainly scaled modelling
and “basic ‘shell theory’”, but without
any software programmes; a full 3D structural analysis wasn’t
applied because of uncertainties over the wood and the prohibitive
cost. Tasker also acknowledges the jointing as very basic - partially
as a result of its computer independence.
Apart
from the wood used in the gridshell, beams and truss, the building
used primarily locally sourced limestone, stone, sand, and wool.
No Portland cement was used at all. In its place an imported environmentally
friendly limestone was used for the foundations, and as mortar
for the stone walls. A second, St Astier lime, this time from
France, was applied to all the above ground walls. The walls were
built up by a contracted stonemason from local stone brought in
from a farmer's derelict dry-stone wall a handful of miles along
the hill ridge. The sand used was from the local quarry. Mineral
wool was used in the external walls and cavity walls, while in
the other openings sheep wool was used. Marketed as Cosywool,
this unusual organic mineral wool came from the Wool Marketing
Board; being made into 'tops' on site, small long sausage shapes
cut from 100 metres of the material. The work took time because
the wool needed repeatedly folding over, but was pleasant on the
hands - unlike many comparable glass and other industrial wools.
 
Image
David Tasker
At
first there was some scepticism about gridshells. They didn't
appear to follow the way the wood wanted to go, rather, it seemed
as if the form was fighting against nature. But soon the challenge
became interesting for those involved, including a forester and
joiner, Malcolm Lemmon. Quite quickly the technical problems of
realising the project, apart though causing mighty headaches,
became fascinating issues with which to wrestle and seek solutions.
Image
David Tasker
Lemmon
found 40 tonnes of larch from a project in Perthshire, which had
foundered and was closing down. Lemmon bought this after checking
its sustainability factors. The timber for the window frames was
Highland Douglas fir - an increasingly popular, and durable, tree
crop in Scotland - manufactured into windows in Edinburgh. For
Lemmon, as for all those centrally involved, it was a steep learning
curve. What analysis there was happened on site as the building
progressed. Happily, once construction was underway the roof turned
out to be not as difficult as Lemmon had presumed. Tasker had
prepared a small experiment with a miniature pine dome model,
and Lemmon used this to see how the wood would respond. From this
he realised that young green larch would work well; the sapling’s
elasticity ensuring the bending needed for the curvature. From
there, Lemmon went looking for the right potential larch, finding
it eventually in one of the Earl of Rosebery's estate's forests,
a few miles south of Edinburgh. Trained to be able to uncover
woods from eye, he hand-picked the larches, and took them away
as part of a management thinning project with the estate. These
were prepared as laths around four metres long, and next, initially
by trial and error, Lemmon began constructing longer laths, scarf
jointing three together to make twelve metre lengths, until there
were two amounts of 20 laths, able to cover twelve metres. These
were made up in two layers of 35mm by 25mm by 600 cm, with the
bits drilled in to form the nodes. The nodes were checked using
pilot bolts, on the jig, to hold each square of the grid together.
 
Image
David Tasker
Once
ready, the grid was put together and bolted up in one day, with
nearly two dozen volunteers helping at the site. Two hours later
the volunteers had manoeuvred the grid into position as part of
the roof. In the event only two joints needed replacing. Completely
floppy, the gridshell was at this point both very supple and fragile
until the boards covering the laths were also put in place. After
this with further boarding applied, and the structural shape forming
around a scaffolding tower and temporary timber struts, the shell
began to co-elesce.
While
the corners were held down by rope, the first two layers of 100mm
boards were screwed into the lattice, the shell, according to
Lemmon, becoming more uniform, as it began to dry out. The board
wood was found from a local forest four miles away, an economic
choice since it was small enough to be cut into shape. In fact,
the whole gridshell cost was minimal, in the region of £2500,
although as Lemmon points out when you add labour, his work and
two intermittent paid helpers, it inevitably increases the cost.
As it was put into place, each layer of boarding soon reinforced
the emerging shape. Alternate layers were placed at 90 degrees
to each other, to reinforce the strength. With three layers across
the whole dome, and four at the edges this produced an effectively
extra-tough roof. An extra complication was that the shell was
being placed onto the hexagon. Domes have been placed on square
and circular rooms before, fitting these proportions easily, but
they have not been set upon hexagons. Not surprising, perhaps,
they do not fit so readily. Lemmon pulled the gridshell dome down
upon the two opposing sides of the hexagon walls initially, until
they began to bend into shape. Once the gridshell dome and boarding
was in place it was covered with a turf roof, and a Rubberfuse
membrane was sourced as the best eco-friendly option available.
Insulation continued to be a problem and cork was eventually applied
to the membrane. The cork, another import, this time from Portugal,
compared well with polyutherene and other polyester insulations.
It was finally completed at the beginning of the year, then covered
with horse and cow dung, and presently sports a thick grass matting.
Before
it went up, no-one knew whether the gridshell would actually work
and although Tasker felt confident there wouldn’t be any
real structural problems, there were quite a few nerve-wracking
days wondering what they were going to say to the funders if it
didn’t work. The load testing was unconventional. Rather
than computer analysis, the building group hand calculated 700
bags of sand which when massed equalled 13.4 tonnes of sand, so
that the deflection on the roof could be carefully measured –
it came in at 25 millimetres, equalling the worst snow cover scenario.
Happily,
the building did work out, and by the summer of 2002 it was beginning
to be used. The building represents a success story for the small-scale
and self-built, and it also demonstrates the tenacity of a small
team. One can easily speculate that were local building contractors
let loose on such an unknown quality as a gridshell, since so
few have any experience of the form, let alone worked on one,
they would price the risk into budget oblivion. Since only one
or two companies have the relevant experience, this must be one
of the main constraints on its growth in use, with specification
and design generally so expensive. The Pishwanton gridshell demonstrates
that with resolve and patience people can construct for themselves.
All those involved state they learned a variety of things from
the construction, and could improve on it if it were being constructed
again. Certainly such smaller-scale applications seem obvious;
offices, chalets, community halls, restaurants; the list goes
on. Gridshell pod roofs could be used for 10 m classrooms both
in, and outside, the Steiner-Waldorf context. Further uses in
a variety of contexts are also easy to imagine.
One
surprise is that gridshells were new to Day. Even if there are
very few, they suit his ‘Spirit and Place’ aesthetic.
He believes the double-curved parabolic form contains considerable
strength, and describes the internal space as a very gracious
and harmonious gesture. All of which helps make the form so satisfying,
in Day’s words, “at a preconscious level". Indeed
the Pishwanton Lothian project deepens the range of forms of this
band of buildings represent, pulling another example of this genuinely
exciting, elegantly ecological and twenty-first century form into
material existence.
 
Image
David Tasker
End. |
