Chemicals added to conventional insulation materials often contain Volatile Organic Compounds (VOCs), which have been implicated in the recent rapid rise in incidence of asthma and severe allergic reactions in western countries as synthetic materials “off-gas” toxic chemicals into our homes.
Hempcrete, and the lime and clay plasters which are applied to its surface, are “breathable” (vapour-permeable), meaning that they allow water vapour to pass through them. In addition, thanks to the porous nature of both the hemp shiv and the lime binder and the air pockets created by the arrangement of particles in the hempcrete material itself, hempcrete is hygroscopic. This means that hempcrete absorbs moisture into the material during times of high relative humidity in the air, and releases it again when the relative humidity drops.
This ability to passively regulate the humidity in the internal space means that when there is excess moisture in the air (for example when cooking, or in bedrooms at night, from the occupants’ breathing) condensation does not get a chance to form on the surface of the wall. This in turn discourages the formation of damp and mould spores, which can be harmful to human health.
The regulation of humidity in the indoor environment to a healthy level (between 40-60% relative humidity) has been shown to inhibit the spread of viral and bacterial infections, allergic reactions, asthma and other respiratory conditions, and reduce the occurrence of mites, mould and fungi.
This ability of hempcrete to passively regulate indoor air quality reduces the need for mechanical ventilation systems, further reducing the energy required to maintain a hempcrete building.
For more information about hempcrete, please see our other blog posts.