A timber and straw home called Koeschi is hidden in a wooded valley in Cornwall, England. Koeschi was designed and built by Joshua Penk between 2009-2011 using materials from the site like timber and straw to be low impact. It takes advantage of solar gain and cooling from trees and a stream. The single-story home blends into the forest and uses few contractors to keep costs low at £81,800. Passive solar and a wood-burning stove provide adequate heat for the open-plan living area.

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A timber and straw home hidden
in woodland.
Koeschi means «house in the woods» in Cornish and, surrounded by
mature trees, this striking modern building becomes part of its landscape.
The timber framed house is designed to take advantage both of solar
gain and the cooling properties of the woodland and the stream that
runs past it. It uses wood harvested from the site and is insulated with
straw bales and sheep’s wool.
Introduction
Truro
Exeter
Bodmin
Koeschi
Key dates
Site purchased : 1960s
Planning permission : 1980s
Revised plans : 2009
Construction : 2009-2011
In nature - Photo © Peter Graham

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Koeschi is set in a wooded valley
which was purchased by the Penk
family in the 1960s. Joshua Penk’s
grandfather built the family home,
and his father went on to develop
two further plots on the site.
Joshua designed Koeschi in 2008,
at the age of 19, and working
closely with his parents, friends,
family and volunteers, he built the
house between leaving school and
beginning his architecture studies
at university.
The aim for Koeschi was to create
a low cost building using natural
materials with low embodied energy.
Great care was taken to ensure the
house has a minimal impact on
the landscape. Aesthetically, the
building is influenced by modernism
and Japanese design.
The 35ha site is constrained, since
it could only be accessed over
the stream that runs through the
bottom of the valley. Large mature
beech and oak trees overhang the
building footprint, and Joshua was
determined that these would not
be felled or cut back. The result
of leaving the trees in place is
that Koeschi is absorbed into the
woodland and gives the impression
of having been there for many years.
Context Plan © Joshua Penk
N

3. French-British collective Libnam3
Building overview
The design was strongly influenced
by the site constraints, and a
commitment to keep costs down
by not using external contractors.
Koeschi was thus built without the
use of scaffolding and all heavy
lifting was done by hand using block
and tackle. The decision to build
single storey was dictated by these
factors, and also works well with
the design ideal of minimal impact
on the landscape. Koeschi is thus
a 220 sq m single storey building
supported on 50 concrete pad
foundations which accommodate
a slope and support structural
Douglas fir posts. The ends of the
posts are protected by home-made
lead sheets.
The main living space is open
plan, allowing for heat to circulate
naturally from the wood burning
stove, which also delivers hot water
and serves an underfloor heating
system. Hot water is supplied from
a Navitron solar thermal panel in
warmer months. Extensive glazing
on the south elevation creates solar
gain.
The large spans in the living space
Pad foundations - Photo © Celia Robbins

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are achieved using engineered
glulam beams. The external walls are
insulated with straw bales protected
on the outside by Bitroc panels and
cedar cladding; they are further
protected by large roof overhangs.
To the interior, OSB board and
timber battens support the
interior finishes which use natural,
breathable materials that do not
require painting, including birch ply
and a pressure-treated gypsum and
wood fibre product, Panelmox. The
flooring is also composed of a wood
fibre and gypsum sheet material
which was sanded and sealed with
a water based acrylic varnish to look
like poured concrete.
Floors and ceilings are insulated
with wool, a by-product of the
production of fleece rugs in Devon.
The green roof was constructed
using bitumen board, a rubber liner
and soil lifted from the site.
Interior - Photo © Celia Robbins

5. French-British collective Libnam5
Technical focus : Use
of wood - a sequential
approach to sourcing
materials
The lightweight wood structure is
integral to Koeschi’s low-impact
design. It allows the building to
be lifted off the ground on the
northern side, which accommodates
a slope down to the stream. It also
facilitates design features such as
the cantilever which projects the
building over the stream on the
northern facade.
Koeschi is a good example of the
use of wood to create a low impact
building with a strong design and
aesthetic. Guided by the principle of
creating a low impact building, wood
was sourced from the site, from local
suppliers and from international
suppliers (the specialist engineered
glulam beams). This demonstrates
a sequential approach to sourcing
materials and making the best use
of available materials on site. Wood
from the site included cedar for the
external cladding, oak for internal
trims and cherry wood for the front
door. Locally sourced Douglas fir
was used for many the structural
Main access - Photo © Martin Penk - Arco2

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Barriers and solutions
Taking time to self-build
Joshua’s advice to self-builders
would be to start small and use a
modular design that can easily be
added to. He also believes that the
design and build process should
not be rushed. Joshua had the
advantage of knowing his site for
many years before the build started,
so he was able to develop the
design over time.
Home-grown materials
The sliding glass doors for Koeschi
were made from home-grown
timber, which turned out not to
be sufficiently well seasoned. This
has resulted in some bending and
warping. Joshua would advise kiln
drying the wood before making the
doors.
Skills and learning
The site was a great opportunity
for informal learning throughout
the build process. Joshua wanted
to avoid the use of contractors as
much as possible, so learned each
skill as he progressed. He developed
the practice of starting a new
process in an inconspicuous part of
the building so that any mistakes
were not too obvious. Through
using online green building forums,
Joshua made contact with a number
of builders who came to work on
the site to share their skills and
learn new ones. These included a
Danish green building expert, and
an architecture student who has
become a great friend of the family.
elements. The glulam beams were
imported as they were not available
locally at the time of the build.
Wood preparation - Photo © Joshua Penk

7. French-British collective Libnam7
Cross-cutting theme:
Natural heating and
cooling
The entire south facing elevation
is glass, with an external expanse
of single-glazing capturing solar
heat in an enclosed ‘sun space’.
The interior walls of the sun space
are triple-glazed. The sun space
thus traps solar heat which is
buffered from the interior by the
triple glazing. Sliding doors can be
opened to let the heat in, or closed
to keep heat out in hot weather. The
northern elevation is permanently
shaded by woodland, and has a
stream running directly beneath it.
In hot weather a large window on
the northern elevation is opened
which draws cool air through.
The occupants have found the
passive solar heating very effective
in spring and autumn when the
outside air temperature is in the
range of around 8-12°C. In these
conditions, strong sunlight will
generate enough heat to raise the
interior temperature to 18-20°C for
a large part of the day. The interior
finishes comprise large expanses
of dense gypsum/woodfibre board
and these have proven effective
in retaining heat for long periods
in the context of this lightweight
building.
South facade © Martin Penk - Arco2

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Stakeholders
Designer/builder/owner : Joshua Penk
Builders : Friends, family, volunteers
Structural Engineer : Matthew Crompton,
www.cedcengineering.com
Timber supply : Duchy Timber, Lostwithiel
Straw : Restormel farm, Lostwithiel
Glass supply : St Austell Glass Ltd
Interior walls and floor panels : The Panel
Agency
Woodburning stove & boiler : Grey Metal,
Glulam beams : Glulam Ltd
Costs
Total cost : £81,800
Cost/sq m : £371 (inc VAT)
NB : labour was not costed on this build.
Koeschi uses electricity to pump
the underfloor heating and for
immersion heating to supplement
the wood burning stove and solar
thermal panels when necessary.
Average electricity consumption
during the first two years of
occupation has been 10-14 kWh per
day. No oil or gas is used.
The residents find that the wood
Performance burning stove provides adequate
heat for the large open plan living
area, especially as the interior
materials were chosen for their
heat-retaining qualities. This means
that in cold weather, the fire is kept
burning for 4-6 hours in every 24
hour period, and the open plan area
remains warm for the rest of the day
without any need for the underfloor
system. The underfloor heating
can therefore be targeted at the
bedrooms and bathrooms which
do not receive direct heat from the
stove.
Solar thermal panels - Photo © Celia Robbins
Contact
Cornwall Sustainable Building Trust
http://csbt.org.uk/