Key concepts in sustainable building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 76

For some time now, proponents of natural building have been highlighting the benefits of
using natural materials in construction, for example stone, timber, earth, clay, straw, hemp,
sheep's wool and reed. Such materials have a proven track record over thousands of years
in providing healthy homes, and in some cases they also boast significant thermal perform-
ance. Moreover, at the end of a building's life, natural materials used in its construction
(if they are not reused in another building) can be buried or left to break down naturally,
rather than needing to go into landfill or be disposed of carefully, as they do not contain
toxic substances.
Not all natural materials are sustainable, however. For example, slow-growing hardwoods
such as oak, while sequestering ('locking up') a lot of carbon, are not able to replenish
themselves quickly enough through natural regeneration to constitute a sustainable re-
source. Others, such as wheat straw and hemp shiv, are fast-growing annual crops, which
in both cases are essentially 'waste' or by-products from a useful crop. These are truly re-
newable, low-impact and sustainable materials.
The UK is not able to supply all of its own timber needs, and timber brought halfway
around the world, whether or not it is from a monitored sustainable forestry, will never be
truly low impact. In the case of stone, despite the presence of a large amount of stone suit-
able for building in the UK, the relative cost of extracting it, and market monopolies, has
led to the importation of 'cheaper' stone from the Far East. Unfortunately, until the real
cost (in carbon emissions) is priced into this market, or until fuel costs rise dramatically
enough to affect market prices, these unsustainable practices are likely to continue.
Natural insulation
Because natural low-impact insulating materials, such as hemp, wood fibre, sheep's wool
and straw, are not yet used in sufficient quantities to be widely available in general build-
ers' merchants and DIY stores, and in some cases remain comparatively expensive owing
to the current relatively low demand, they are often overlooked in favour of conventional
synthetic products. However, there are great benefits to their use.
In particular, they are produced from materials that are sourced locally, and their manu-
facturing processes are often relatively low in energy. Lightweight insulation quilts made
from natural fibres do usually contain a certain amount of synthetic polymer binder or
chemical fire retardant, but denser natural insulations that are used as a solid walling ma-
terial, such as straw bale and hempcrete, do not contain such additives.