Minegu-en

1. 146
This bioclimatic octagonal
house showcases wood and clay
construction.
Key dates
Site preparation : 2009 to
2010
Project conception : 2010-
2011
Construction : 2012-2014
After living for 30 years in a dwelling built around a trailer, Roland and
Bénédicte wanted to live in compact, 8-sided house designed to boost
their supply of solar energy. They relied on the sun for their hot water and
on wood for heating. Fully integrated in its surroundings, their house has
been built with eco-friendly materials (earth, wood, cellulose wadding).
Introduction
Saint Brieuc
Quimper
Vannes
Rennes
Mellionnec
Minegu
Overview - Photo © Servane Guihaire - Constructys Bretagne

2. www.libnam.eu 2
The main contractors lived for 30
years in a wooden house attached
to a large trailer. Wishing for a
more efficient house, they opted
for a compact, simple house with
unusual shapes, reminiscent of their
former home. They also wanted a
single level living space, light and
easy to heat.
Having been conscious of eco-
construction for many years, it was
obvious to them to use natural
building materials and renewable
energy. They chose a bioclimatic
design to make the most of the plot
conditions; a south-facing hillside
overlooking 14 acres of woodlands.
In this isolated, under-developed
area, it was vital for the building to
blend fully into its surroundings.
Context
Finally, the main contractors wanted
the wood burner flue positioned in
the middle of the house. With the
designer’s help, they came up with
a single-level house of 81 sq m,
with buffer rooms to the north, bay
windows to the south and a heat
absorbing wall in the living area.
The octagonal shape of the building
enables it to harvest and store the
sun’s energy throughout the day.
Plan © Yoann Lanoë - Biosmose

3. French-British collective Libnam3
Building overview
Concrete foundations surround
80mm cork insulation and 150 mm
thick limecrete, on top of a 200 mm
flat-bedded building stones.
The main structure is Sitka spruce
timber frame with I-beams (240 mm)
which enables it to reduce thermal
bridges (German brand Steico). The
building has a pitched roof with
the highest point in the centre. The
Douglas fir roof structure which uses
a lean production method, and does
not require supporting pillars, is set
around the wood burner flue. This is
a design feature, made possible by
a galvanised steel ring, linking the
roof trusses and the chimney flue.
Wall structure from inside out:
wood cladding (12 mm) - air gap
(5 cm)- vapour-barrier (Sd=0.5)
- Kronospan boards (15 mm) - I
beams/ insulation- glues Pavatex
(rain barrier KN1) – batten - larch
cladding.
Roof structure from inside out:
poplar cladding (12 mm) - air gap
(5 cm) - vapour-barrier – insulation/
frame - braced Agepan board
(Sd=0.5) - rain barrier (SD=0.2) -
roof rafters (60x40 mm) – batten -
slates.
The windows are self-cleaning
double-glazed units (Bioclean), with
anti-reflective effects (Minco brand).
Insulation is made of blown cellulose
wadding (22 cm in walls and 38 cm
in the roof), except for partition the
walls, which are insulated wood
wooll (Isonat) or « wattleanddaub”
(mix of earth and straw).
Some partition walls are boarded
with gypsum boards (Fermacell), or
plastered with earth containing flax
straw.
Timber frame - Photo © Christophe de Quelen - Menuiserie de Quelen

4. www.libnam.eu 4
Hot water comes from solar energy
harvesters, with an electric boost.
Ventilation is natural.
A wood burner is placed in the
middle of the octagon between
a supporting wall made of
compressed earth bricks (mounted
in an oak frame). This wall enables
heat storage from the wood burner
and brings inertia heating into the
house. It also brings hydrometric
balance.
A 3 cubic meter rain water tank was
installed for watering the garden.
Technical focus :
Compressed earth
bricks
The house is timber framed. By
definition, it has low thermal mass
compared to wall based structures.
To regulate the inside temperature,
especially during winter and
summer months, added thermal
mass can be useful. Clay, a natural
material available underneath the
Central core - Photo © Christophe de Quelen - Menuiserie de Quelen

5. French-British collective Libnam5
top soil, can be used for this.
Either mechanically or manually
rendered, earth can be moulded
into bricks. Earth brick can only
be composed of earth. Some also
contain binding agents (lime) or
fibres (straw, hemp). They can be
baked in kilns or used «raw» after
drying out.
For this build, the main contractors
chose compressed earth bricks.
They are unbaked and produced
from sieved earth that has been
heavily compressed (density : 2.2).
The compressed earth bricks
contain clay (15%), gravel and silt.
No lime, cement or sand was added.
The earth was sieved to 10 mm.
A mobile press gives a 40 tons
thrust for compression (150 bar).
Each brick measures 10x20x30 cm
and weights 13 kg.
On the building site, they can be
laid on any of their sides and glued
with liquid earth slip, on a moist
base. The compressed earth bricks
are more efficient next to a sunny
window or heaters, to store and give
off heat in the living space. However,
due to a lack of study and analysis,
bricks cannot be used for load
bearing walls. Also, bedrock can
be essential, to avoid the capillary
rise of water. The foundation must
be reinforced for high walls due to
their weight. Finally, their edges are
fragile but are generally plastered
over for finishing.
Stove and earth brick - Photo © Servane Guihaire
- Constructys Bretagne

6. www.libnam.eu 6
Barriers and solutions
Building an unusual shaped
house in a remote area requires
good communication with the
town council to secure successful
planning application. The planners
required the construction of a small
dwelling, which favoured the use of
wadding instead of straw bales to
reduce the thickness of the walls.
The supply of material was not a
problem: the wooden frame, the
bricks, wadding, and flax straw all
come from Brittany. The earth used
for the cob comes from the site
itself. Other materials come from the
usual suppliers. It is worth noting
that the nearby cement factory was
delivering lime concrete for the first
time.
The main contractor was project
managing himself. On a technical
level, it was difficult to obtain reliable
and independent information. In the
world of eco-construction, skills are
scattered. Trades are always looking
for innovation but can only master a
limited set of skills and knowledge.
Fortunately, some experts, such
Earth bricks - Photo © Servane Guihaire - Constructys Bretagne

7. French-British collective Libnam7
as Jean-Pierre Oliva, published
reference books.
Amongst the different stages,
groundwork was the most
challenging due to the rocky terrain,
and the groundwork, sewage and
connection to services represent
£11,600 of the budget.
The erection of the frame was a
technical challenge (see above) and
generated 40/50 % of additional
costs.
The design of the internal layout
demonstrates the simplicity of using
earth as a building material. It can
be reshaped creatively ; there is no
waste and no risk of skin irritation
for the user.
To master the different techniques,
the builders tried different
experiments, visited other sites,
exchanged information with
colleagues or updated their
training (example : Tiez Breiz,
ARFAB). The designer, on top of
his qualifications, has specialised
in eco-building (Eskemm training).
The association ECOB, created to
coordinate craftsmen in central
Brittany, enabled the exchange
of eco-construction knowledge
between them.
Everyone improves their skills
during builds such as this one: for
example, the mason poured his first
limecrete slab .
In hindsight, if the main contractor
could start again, , he would modify
the eaves to maximise the passive
solar heat, due to the height of
the building and the absence of a
second level.
South facade - Photo © Servane Guihaire - Constructys Bretagne

8. 8
Stakeholders
Main contractors : Roland Le Bouëdec &
Bénédicte de Ville d’Avray
Designs : Yoann Lanoë
Groundwork : Jacky Louargant (Mellionnec)
Masonry : Lachiver (Gurunhuel)
Timber frame, insulation, openings :
Menuiserie de Quelen (Locarn)
Electricity : Eric Berthier (Trémargat)
Solar energy : Energies libres (Noyal
Muzillac)
Airtightness testing : Alexis Trubuil
(Plounevez-Quintin)
Mobile sawmill : Letur (Sizun)
Compressed earth bricks : Terra Terre
(Spezet)
Walls, plastering, cladding : self-build
Costs
Plot : owned by the contractors
Design : £1,569 including tax
Build costs : £1,176 per sq m or nearly
£94,000 (without the site), including nearly
£12,000 for ground work.
The building underwent an
airtightness test, although this
was not required on the planning
application.
The results were above the standards
of the 2012 thermo-regulation
and the BBC-EFFINERGIE® (Low
consumption building certification).
The thermal resistance thanks to the
cellulose wadding reached : 5.5 sq
m per kWh for the walls and 9.9 sq
m per kWh for the roof.
The annual energy consumption of
the house is 38 kWh/sq m. It uses
between 1 and 1.5 cords of wood
Performance
Earth partition - Photo © Servane Guihaire - Constructys Bretagne
for heating every winter to reach
a temperature of 19/20 degrees C
inside.
Overall interest in the building
was confirmed when an eco-
construction open day in November
2012 attracted 150 visitors.
Contact
Constructys Bretagne
www.constructys-bretagne.fr