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| Under construction |
Location:
Kensington,
Melbourne, Victoria
Type of
Build:
Extension
and separate workshop
Owner:
Grant
Randle and Shelley Hosking
Designer:
Barbara
Weimar Architect
Builder:
Grant
Randle - Owner Builder
Size:
80 sq.
new; total 115 sq. including retrofit of
part of existing house; plus 15 sq. workshop/brewery
Cost:
$430,000
(est)
Date of
construction:
Commenced:
September 2014
Purpose
of Build:
To
provide a new kitchen, dining and living room and a link, between the old weatherboard
home and the new extension, containing a music room. The design uses high
windows to bring northern light into the extension which is to the south of the
existing building.
Choice of
Material:
Grant and
Shelley wanted to use a zero carbon material in their extension and researched
several alternatives including using straw bale, but straw bale would have
meant thick walls, taking up valuable floor space on an inner city site. As
well as choosing to build with hemp for the walls and as the ceiling insulation
Grant and Shelley have chosen to use other low carbon, natural materials,
choosing timber frame and beams over steel. Grant and Shelley came across hemp
building while researching sustainable design on the internet. They chose hemp
for its thermal effusivity resulting from the unique combination of thermal
mass, thermal resistance and moisture absorption properties. They were also
attracted to the simplicity of the basic materials, the robustness compared
with strawbale and the possibility to self build with limited skills.
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| Inside under construction |
Zone 6 -
Mild Temperate
Local
Council:
Melbourne
City Council
Obtaining
Approval:
The
building application was initially lodged with a drawing note referencing HCA (Hempcrete
Australia) material “installed as per manufacturer’s recommendations”. It did
not explicitly mention the NCC approval. When the binder was changed to the
Australian Hemp Masonry Company (AHMC) binder, an engineers report was provided
to the private building surveyor. Melbourne City council had no issues with the
hemp walls during the planning approval stage and the building surveyor has had
no concerns to date.
Construction:
The
walls, insulation, MgO Board walls and kitchen installation are being carried
out by the owner. A builder was contracted to do the concrete slab, timber
frame and roof.
Footings:
Concrete
raft slab on ground with expanded clay aggregate balls (Clinka) underneath and
EPS (expanded polystyrene) around slab edge to achieve an R1.8 rating for the
entire slab.
Floor:
Polished
concrete in living and dining room; Cork and linoleum in kitchen.
Walls:
300mm
hemp walls, using Australian Hemp Masonry Company (AHMC) binder, cast around
90mm pine frame. Render to be decided.
Windows:
European
Timber Windows, triple glazed in the highlights and double glazed elsewhere.
Ceiling:
10mm Magnesium
Oxide board on timber battens at 450mm centres, with hemp insulation 150mm
thick, using an AHMC ceiling mix of 5.5kg of hemp to 4.5kg lime, and no sand.
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| Hemp/lime as ceiling insulation. Photo:Shelley Hosking |
Roof:
Corrugate
Zincalum with silver batts mounted under rafters to provide a thermal siphon
effect to limit thermal load from the attic. Pitched roof chosen to provide
solar panel mounting without an ugly frame, easier hemp placement at the top of
the wall and thermal barrier between roof and ceiling.
Heating:
Wall
mounted hydronic heating.
Cooling:
Passive
ventilation. Design includes high opening windows to assist with ventilation.
Wall
construction:
Grant and
Shelley, with family and helpers built the walls using a 120 litre pan mixer
purchased from through e-bay. Prior to commencing construction Grant and
Shelley had attended a 3 day hemp building workshop with Hempcrete.
Formwork:
Geoplast plastic
formwork and OSB (oriented strand board) reinforced external with timber. The
6mm OSB is not stiff enough for formwork on its own. Grant and Shelley only
used the 6mm OSB as they inadvertently received it with the frame for bracing. The
sheet bracing was replaced with steel strap, and the
surplus used as formwork. They have also purchased some concreter’s form ply for
formwork.
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| Geoplast and OSB formwork |
Section Diagram:
Technical
issues:
Grant and
Shelley found it difficult to get information on hemp building.
Advice/Recommendations:
If using
plastic formwork design the house to fit the formwork. Try to avoid double and
triple studs in the timber frame by adding timber spacers between the studs.
For the big
lintels and beams where they only had 50mm cover, they used permanent formwork
of wood wool board from Knauf (Heradesign), rather than risk the hemp falling
off.
For
window and door openings, Grant and Shelley suggest extending lintels 300mm
past the opening so that supporting double and triple studs can be fully
encased in hemp.
They also
suggest using timber bracing a they had in a workshop they attended..
For more
helpful tips see Grant and Shelley’s blog below.
Contact:
Read more
about Grant and Shelley’s hemp build at hempcretehome.blogspot.com