Key concepts in sustainable building - The Hempcrete Topic: Designing and Building with Hemp-lime - page 75

ric of the building where air can leak out - or in. These increased levels of airtightness
in buildings have the effect of reducing the natural ventilation of the indoor environment
which was historically the case.
Many synthetic insulations contain toxic chemicals or volatile organic compounds
(VOCs), mainly in the form of adhesives and fire retardants added to the material, which
are known to give off harmful gases into the indoor atmosphere. Because of this, the
poor indoor air quality in some buildings in which high levels of synthetic insulation are
combined with high levels of airtightness is increasingly becoming a cause for concern.
The solution to this problem is usually to install mechanical ventilation and heat-recovery
(MVHR) systems into buildings at great expense, thereby ensuring even more consump-
tion of fossil fuels in their operation during the lifetime of the building. There is growing
evidence that in some instances, especially where mistakes are made in detailing of MVHR
systems and/or air vents, indoor air quality quickly falls far below standards fit for human
habitation, owing to both the minimal ventilation and the high concentration of synthetic
materials containing VOCs. 4
Until we have proper carbon profiling and LCA of individual insulation materials, allow-
ing meaningful analysis and comparison of the full range of materials available, it will be
difficult to make truly informed choices of insulation material. Sadly, many of the syn-
thetic insulation materials are produced by powerful multinational companies, who are a
powerful lobby group with the UK government, which has obvious implications for regu-
latory decision-making about the true carbon cost and health costs of such materials.
Sustainable construction materials
Clearly there is a need for truly sustainable insulation materials: ones that are produced
locally to where they are used, take their raw materials from a renewable source, and have
the minimum of energy use associated with their production and use. To help reduce car-
bon emissions once in use, they must also achieve a high level of thermal performance.
The type of material urgently needed if we are to make meaningful progress in reducing
the huge contribution made by the construction industry to CO 2 emissions might best be
described as a low-impact material. This is one that represents minimal consumption of
fossil fuels, has no negative impact on human health, and does not cause any harm to the
wider environment in its production, use or disposal at end of life.