Rosemoor (Pilkington Cob Shelter)-en

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A cob and timber roundhouse
shelter in a beautiful garden
environment.
The Pilkington Shelter is a new building, built using ancient traditional
techniques and materials. It fits well into the stunning environment
cultivated by the Royal Horticultural Society. The cob and timber frame
shelter provides shelter for visitors from the rain and a cool haven to
retreat to when temperatures are high. It uses wood and earth obtained
from the site.
Introduction
Truro
Exeter
Great Torrington
Pilkington Cob Shelter
Key dates :
Planning permission : 2011.
Construction : 2011-2012.
Photo © Jan and Jerry Sharpe - J&J Sharpe

2. www.libnam.eu 2
The Pilkington Shelter is set in
the grounds of the RHS gardens,
Rosemoor in Torrington. The land
was given to the Royal Horticultural
Society in 1988 by Lady Anne Palmer,
who had a great love of horticulture,
which led her to many exotic places
around the world, discovering
and collecting new plants for her
collection. The grounds covered 40
acres, including pasture land and her
original garden.
The grounds have now been
transformed into an array of stunning
formal and informal gardens, and
Bicentenary Arboretum; it is used
for information, training, events
and most of all, pleasure. All of the
new buildings on the site have been
designed not only for their function,
Context
but with great care to ensure that they
blend in well with the environment.
Thus, when the client was choosing
what to build as a new shelter for the
public to use, they agreed on a design
which not only suited its purpose,
but fitted in with its environment.
It is aesthetically pleasing, with its
timber roof, soft lines and earth
hues, blending in with the woodland
behind. This natural, elemental
design was the work of Peter Hall,
of Van Der Steen Hall Architects, of
Chagford, Devon, and was influenced
by the principles of Rudolf Steiner,
an Austrian philosopher, reformist,
educationalist, architect and esoteric.
Drawing © Van Der Steen Hall Architects

3. French-British collective Libnam3
The Pilkington Shelter is 5m high
and has a floor space of 25 m² and,
in keeping with the design principles,
was built using sustainable resources,
most of which were acquired from
site. The timber was sourced from
their woodland, and soil/clay
obtained from the excavation of the
foundations and the gardens was
used for the cob. A local contractor
and heritage build specialist, Jerry
Sharpe, of J&J Sharpe, was hired to
build and act as project manager
for the project. Local carpenters
were hired to build the roof, thus,
reducing costs and minimizing the
environmental impact on site and
through travel and haulage.
The single storey cob building stands
on strip foundations, which were dug
down to reach firm ground to ensure
Building overview
stability. These were then filled with
reinforced concrete with a stone
plinth built on top. The stone plinth
is 500mm wide and was built using
local stone and lime mortar.
The walls are made out of mass cob,
which is set on top of the plinth with
four tapered windows. The windows
were formed using forms made from
plywood to act as the shuttering. On
completion of the walls, the forms
were removed and slate sills were put
in.
The interior of the shelter kept
to the original principles of the
design. The floor was formed using
limecrete. Limecrete is a material
made from mixing natural hydraulic
lime, aggregate and water. The
limecrete for this project was made
from yellow chippings, course sand
from Somerset and natural hydraulic
lime five. To provide a suitable base
for this, the surface of the floor was
first compacted, then levelled out,
Photo © Jan and Jerry Sharpe - J&J Sharpe

4. www.libnam.eu 4
(blinded) with sand and covered with
a geotextile matting membrane. The
limecrete was then mixed by machine,
barrowed onto the spot and levelled.
The stunning roof design is made up
of seven panels, with seven different
pitches. Local carpenters Tim Mills
and Jack Bennett, undertook this
complicated task, using local larch
to form the structure. The roof sits
on wide wooden wall plates which sit
directly on the cob walls. Sitting on the
wall plates are two A frame trusses,
(shown in the picture above), which
were joined with purlins and a ridge
beam. From the trusses, hip rafters
then formed the roof framework to
the wall plates. The roof was then
finished with larch boards.
The interior and exterior walls were
finished with lime plaster. Lime plaster
is often used in conjunction with
cob as it allows the walls ‘to breath’
allowing the transfer of moisture
which is essential to the integrity and
longevity of the material.
Finally, a French drain was constructed
around the building. This was formed
by digging a trench around the
outside of the shelter. The trench was
lined with a membrane of geotextile
matting which stops the earth from
blocking the drainage system. A
perforated pipe surrounded by clean
chippings which allows the free flow
of water, takes the water away from
the area of the shelter to nearby land-
drains.
Photo © Jan and Jerry Sharpe - J&J Sharpe

5. French-British collective Libnam5
Technical focus :
Use of Cob as a viable,
sustainable building
material
Using cob construction for the
Pilkington Shelter at Rosemoor was
fundamental to the initial design
principles. It harmonizes with nature
and its environment by the use
of earth elements from the site,
and by using predominantly hand
working building methods and local
companies for everything from the
architects to the contractors, the cob
helped to ensure a low impact build.
As well as fitting in with the design
principles and being a low impact
building material, cob is a local
traditional building material used
widely in the South West of England.
There are many cob houses and barns
in the Devon area, some which date
back 500 - 600 years.
The Gardens and foundations of the
building supplied the soil, which had
a suitable clay content to allow for
this. In order to make cob the soil was
mixed with chopped barley straw and
water. This can be mixed by hand, but
in this case, because of the quantities
needed and time constraints, a digger
was used to mix the material.
Time is a critical issue when working
with cob, as adverse weather
damages the cob. This is because the
cob takes a much longer time to ‘go
off’ compared to cement, and during
this time extra water will damage the
structural integrity of the material.
For most of the year, Devon has one
of the highest average rainfalls in the
country, so time is of the essence. The
use of a digger reduces the number
Photo © Jan and Jerry Sharpe - J&J Sharpe

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of people needed and the time taken
to mix the material and speeds up the
process.
Cob also needs to be built in stages
called lifts. This is where a section
is built and allowed to dry out. This
enables the material to develop
structural strength as it ‘goes off’,
which is the time that it takes to dry
sufficiently before the next lift can
be added. A variety of factors affect
the time it takes, including sunlight,
humidity, wind, size of wall and
mixture. In the case of the shelter at
Stakeholders
Architects : Peter Hall Dip Arch, RIBA AABC of
Van Der Steen Hall
Contractor : J&J Sharpe Ltd
Carpenters : Tim Mills and Jack Bennett
Costs
The project cost a total of £40,000 which was
funded by a donation to the RHS.
Rosemoor, the contractor decided
that lifts of 400 mm, set on a 500
mm plinth would be appropriate.
Although the mixing and moving
of the cob material was done
mechanically, the mix was forked and
compacted in the traditional manner
by tamping, which is stamping the
mix down as they walked along the
wall. Each lift was allowed to dry and
become firmer, then the edges were
pared back (cut back), to the desired
shape using hand tools.
Drawing © Van Der Steen Hall Architects
Contact
Petroc
www.petroc.ac.uk