Civil Engineering Reference
In-Depth Information
walls, are probably the elements that will be the most unfamiliar to designers and builders
of conventional buildings. Other aspects of hempcrete construction, such as the timber-
stud framing, the shuttering, the mixing of a binder with an aggregate, and the plaster or
cladding finishes, will be familiar to most people in the construction industry.
Internal walls
Hempcrete is often specified only for the external walls of a house, because of its insulative
properties, but there is no reason why it cannot be used for internal dividing walls as well.
Hempcrete internal walls create a continuation of the 'feel' of the building into the interior
space, and provide a good thermal and acoustic barrier between rooms. Interior hempcrete
walls can be cast at a much-reduced thickness, and they make it easy to avoid the use of
non-natural or high-embodied-energy materials such as gypsum plasterboard and synthetic
insulation to construct stud walls.
Using hempcrete for internal walls also allows the continuation of the use of natural fin-
ishes such as lime or clay plasters throughout the interior space, although in many cases
architects apparently do not consider this, or see no benefit in it. Switching to gypsum
board and skim for the internal walls may influence the moisture-buffering capability of
the internal structure, and also inevitably creates an awkward cross-over point somewhere
between the two types of material, which in our experience usually leaves the interior fin-
ish feeling disjointed and clumsily stitched together. An alternative to casting hempcrete
for the internal walls would be to use a carrier board suitable for lime plaster, such as wood
wool board, for internal stud walls. It may be that the failure to continue the use of natural
finishes throughout the building is a reflection of designers seeing them as a 'necessary
evil' for finishing the hempcrete, rather than as a beautiful and functional feature which
enhances the comfort of the building's occupants.
Wall structure and finishes
The lime in the hempcrete binder, together with the breathable nature of the cast material,
serves to protect the hemp aggregate and the timber frame from rotting. This means that
untreated softwood can be used for frame sections that are encased in the cast hempcrete,
with no extra measures to protect it from moisture. Although, to our knowledge, no specif-
ic research has investigated the longevity of untreated softwood in this situation, this is a
generally held principle across the industry, and countless examples exist (the vast major-
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