Hemp construction advantages
Hemp-lime has a low impact on the environment and its carbon sequestration and storage capacity are a significant benefit of the material. During photosynthesis, the hemp plant absorbs carbon dioxide from the atmosphere during the day, converting carbon to biomass and exhaling oxygen. When the hemp is subsequently used in construction, the carbon within it is locked away for the life of the building. Therefore, using hemp within the structure of a building can be better than zero carbon, sometimes referred to as carbon negative. 108kg of CO2 can be locked away in 1m3 of lime-hemp.
A lime-hemp wall of 200mm depth provides levels of thermal and acoustic insulation well above regulation standard. It also regulates the internal relative humidity and temperature swings ‘through hygroscopic material behaviour, contributing to healthier building spaces and providing effective thermal mass’.The building envelope is vapour permeable which allows moisture in the building to migrate out and eliminates the likelihood of condensation on internal faces.
Simplification of the construction process with fewer materials and layers is also a benefit. It is usually where different layers or materials meet that failure occurs and it is also more cost effective to have one material performing many functions rather than many materials each performing a single role. For example, in a standard timber frame construction you may expect to find a layer of insulation, a vapour barrier layer, a breather membrane layer and a sheathing layer to name but a few. However hemp-lime itself can perform all of these functions and, due to the reduction of connections, a more air tight envelope can be achieved.
Unlike concrete, lime’s mechanical flexibility allows movement without cracking. If a crack does appear the lime acts in a manner which can self heal. Any moisture ingress re-activates the lime around the crack, filling the void and sealing the material. This flexibility also allows movement with the frame, reducing the risk of gaps appearing between hemp-lime and structure.