Key concepts in sustainable building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 86

Figure 4. A building with high thermal mass 'buffers' daytime and night-time temperature variations,
maintaining a steady internal temperature and thus reducing the costs of heating or cooling the
building.
Hempcrete combines the naturally insulating hemp, a cellulose material, with a lime-based
binder, which gives a moderate density to the cast material as it sets hard. For this reason,
hempcrete is unique among natural sustainable materials in offering a substantial degree of
insulation combined with a good amount of thermal mass. In comparison, cob or rammed
earth has high thermal mass but virtually no insulation value, and straw bale has good in-
sulation value but virtually no thermal mass. Hempcrete is unique in providing both good
insulation and good thermal mass.
The slow release of the heat stored in a hempcrete building's thermal mass, when the heat
source is turned off, means that there is less fluctuation between extremes of temperature
inside the building. The thermal mass in the walls buffers changes in internal temperat-
ure, meaning that the indoor temperature in a hempcrete building is slower to respond to
changes in the outside temperature (increasing cold or heat) than in a building with less
thermal mass.
This aspect of its thermal performance, combined with its good insulation value, makes
hempcrete very efficient at regulating and maintaining internal temperatures. The build-
ing's heating and/or cooling system therefore uses less fuel than it would in an environment