Performance of hempcrete in a building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 137

Fire resistance
The formal testing of the fire-resistance properties of hempcrete has been limited; carried
out mainly on proprietary products (both pre-cast and cast in situ) to test compliance with
national regulatory regimes. However, the density and nature of hempcrete, with the plant-
derived component encased within its lime binder, means it is very difficult to set fire to
it. Moreover, the standard detail of cast-in-situ hempcrete encasing a timber frame means
that the hempcrete forms a barrier between the timber structure and any fire.
Bevan and Woolle y 1 cite fire testing carried out in France on a 250mm-thick wall of hemp-
crete blocks laid in lime mortar. The wall remained intact for 1 hour 40 minutes, although
the mortar joints failed. No re-ignition or emission of toxic gases was noted. It is assumed
that a solid cast wall of hempcrete would offer a superior fire resistance. These authors also
comment on the fact that while the hemp shiv is flammable in its loose form, hemp does
seem somewhat less flammable than comparable materials in some of its other forms, for
example as hemp paper.
In terms of the resistance of cast-in-situ hempcrete to fire, Daly et al. report that the BRE
Group in the UK carried out:
a fire resistance test on a 3m x 3m Tradical ® Hemcrete ® , non-rendered or
plastered, wall in accordance with BS EN 1365-1:1999. The wall was subject to
a vertically imposed load of 135kN and was cast from layers of hemp-lime mix,
poured into a mould, and included eight vertical timber studs. The internal face
of the wall was exposed to the fire and it resisted for 73 minutes in respect to in-
tegrity, insulation, and load-bearing capacity. 2
The same authors note that testing undertaken by the French manufacturer Isochanvre pro-
duced results that indicated that hempcrete is a “non-flammable material”, with fire-res-
istance performance improving over time as the binder continues to carbonate (this time
factor depends on the composition of the binder: see Chapter 16, page 215 ) .
In a conversation with ourselves, Graham Durrant of The Limecrete Company provided
anecdotal evidence which appears to support this finding. A fire that broke out in a rooftop
upstand on the Sustainable Enterprise Centre at Bradford University, shortly after it was
constructed, resulted in damage to the timber cladding but not the hempcrete. The structure
was a twin-frame design, with the structural timber frame on the internal face of the wall,
and an external, non-structural frame to support the timber cladding. The cladding burnt