Civil Engineering Reference
In-Depth Information
Other ideas for a low-embodied-energy plinth, which probably warrant further investiga-
tion, although to date we have never seen them used for hempcrete walls, include rammed-
earth car tyres (a cheap - usually free - recycled material filled with a suitable subsoil ex-
cavated from the immediate area) and gabions filled with relatively small rocks or rubble
from site.
If you want to use either of these solutions, it is worth trying to assess the potential carbon
savings associated with the method. Ensure that a structural engineer has calculated that
your plinth design is able to support the weight of the building above, and has signed off
on this. In addition, it is necessary to consider very carefully how the DPC, if used, will
work in conjunction with either method, and also how the timber frame could be securely
fixed.
Damp-proof course
The standard DPC will usually be some kind of rubberized, plastic or chemical synthetic
material, although if you happen to have a lot of reclaimed slate lying around, you can do
what they used to do in some vernacular buildings and use coursed overlapping slates to
provide a damp-proof layer in the wall. If you have to buy the slate, this option will be
significantly more expensive than plastic DPC. Also, unless you want to spend an absolute
fortune, any new slate you buy at the moment is likely to originate in Portugal, Spain or
even further afield and therefore has high embodied energy as a material.
Assuming you are using the usual rubberized DPC on a roll, there are various ways of
working it into your plinth design, depending on the plinth construction and the floor detail
inside. As well as lining the top of the plinth, a vertical damp-proof barrier is also required,
to resist lateral movement of water through the plinth from outside. Where exactly the ver-
tical layer should sit within the plinth depends partly on how you are proposing to insulate
the plinth (see below). If your floor is not breathable, you will be including a damp-proof
membrane (DPM) in the floor build-up, and you can simply overlap this with the DPC in
We have received one anecdotal account of hempcrete de-bonding from and shrinking
away from plastic DPC as it dries. While this has never been our own experience, and the
effects of gravity would seem to make it unlikely, the potential for this problem to occur
and cause issues with airtightness should be considered during the design stage, and if ne-
cessary testing should be carried out before building commences. Such an issue might be
resolved through the use of an alternative binder with different shrinkage characteristics,
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