An investigation of the thermal properties of hemp and clay monolithic walls

The monolithic walls of hemp-lime construction enclose and protect a structural timber frame to provide a healthy, breathable building fabric that meets current UK building regulations. It has been proposed that by using hemp as a building material it is possible to actually remove carbon from the atmosphere. Whether or not ‗hemp-crete‘can be considered carbon sequestering, or even neutral, depends largely on the binder. All the lime based binders have high embodied energy, meaning they limit this possibility. Earth construction uses clay as the binder. Could clay substitute for lime in hemp-crete? This experimental research focuses mainly on the thermal properties of stabilised and unstabilised hemp-clay blocks which are tested using a transient heat-transfer probe to measure thermal conductivity, volumetric heat capacity, and derive thermal diffusivity and effusivity. Results are compared with industry-published data for hemp-lime (eg Lhoist, 2009) and found to be similar. The results of the experiments and the literature review indicate that the use of clay as an alternative binder has potential to reduce the environmental impact of the hemp-binder method and facilitate the move towards developing a building material that can used for new build or renovation works, that removes carbon from the atmosphere at this time of need

An initial report into thermal performance of hemp and lime wall sections in the wise building at CAT

Hemp and binder (e.g. Lime) is an insulating wall matrix formed around a timber frame. It has multiple environmental benefits including sequestering carbon dioxide from the atmosphere into a building‟s walls and is thus of interest in the current climate situation. However the thermal performance of the matrix when evaluated using the steady state thermal conductivity (i.e. rate of heat transfer) is not as effective for the same thickness as other insulations. The world however is dynamic and in the Haverhill Housing Project monitored by the Building Research Establishment (UK) two hemp and lime houses, despite having a worse steady state thermal performance on paper, significantly outperformed comparative standard houses (BRE 2002, 2003). The reasons for this unexpected performance are not clarified although the heat storage capacity and the moisture handling ability of the matrix are possibilit ies. Hemp and binder matrix has been shown to have considerable moisture handling and heat storage capabilities but how or whether these improve thermal performance is not clear. All the tests reported so far have been on the same binder yet there are many potential binders and each will change the properties of the matrix and each has a different environmental legacy. To further clarify the in-building performance and to compare a range of binders, 5 different binder test wall sections in the Welsh Institute of Sustainable Education building at the Centre of Alternative Technology are being extensively monitored for heat flux, temperature and moisture movements. This paper is an initial report of this experiment