JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - o - 97

Choosing to build with hemp

A worker spraying hemp

Highly compressible and resistant, hemp fits perfectly to wooden structures with its low heat conductivity

Healthy walls that breathe
Hemp concrete is an environment-friendly insulation filler material
that combines the properties of hemp
and lime. Applying it over a wood
frame is consistent with standard
construction principles. It is sprayed
horizontally into a temporary or permanent form for concrete, or applied
directly to a masonry wall. It provides
well-distributed insulation and signifi-

Focus
Hemp concrete properties:

* Heat and sound insulation
* Biodegradable, non-toxic material
* CO² sequestering material
* Ductile material
* Resistant to insects and mould
* Resistant to rodent damage
* Regulates the ambient humidity
* Won't settle

cantly reduces the occurrence of thermal bridges. Hemp is highly compressible, and so it is resistant. It has low
heat conductivity (and also provides
good acoustic insulation), is highly porous, and it contains microbubbles of
air, which are not heat-conducting either. Thanks to its porosity and moisture regulating properties, the thick
wall releases water vapour during the
summer for cooling and sanitizing effects, and stores it during winter, contributing to heating. The phenomenon
is comparable to a merino wool sweater. Both are "breathing" materials that
allow water vapour to pass through
and evaporate naturally. In the case of
hemp concrete, this helps regulate indoor humidity and avoid the thermos
bottle effect that occurs with passive
houses, for example, which age badly
due to the development of humidity
and saltpetre.
Since 2012, hemp concrete has been
subject in France to professional rules
for work completion as defined in the
DTU 20.1, a 50-page code-of-practice
booklet ("Utilisation of hemp mortars
and concrete") published by CSTB,
the French technical and scientific

centre for the construction industry.
These measures will help expand
the building capacity for this type of
concrete. Its performance currently
exceeds the assessment criteria for
thermal performance and its production process shows a positive carbon
balance, due in particular to the quantity of CO 2 captured during the hemp
growing period. It gives rise to a clean,
silent worksite, since it requires no
heavy construction equipment or installation of oversized foundations.
It is also a 75%-renewable resource.
For projects in protected areas like
regional nature parks, for rehabilitating eighteenth- or nineteenth-century
buildings, and for new construction,
it is beneficial for both people and the
buildings.
Grégoire Dumont concludes: "As an
architect, I have become a conveyor of research and experimentation. My models
are transmissible and reproducible. I'm
supporting regional development by remaining creative and innovative. Hemp
concrete is still a niche market, but I'm
confident that it will come to the fore."

No111 March 2017

More information:
www.dumont-legrand.fr

/ jec composites magazine

Feature Construction

wins over the teams, architects, project
management, engineers, and masons. It
generates interaction with all of the construction teams, at both material and
human levels. It makes it possible to have
nice thick walls (bringing to mind adobe
walls) and fits well into country or stonewalled village environments, or in the old
parts of towns."

http://www.dumont-legrand.fr

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