What is Hempcrete?
Hempcrete is a natural, breathable, medium density insulation material, which also has thermal mass (heat store). Hempcrete is made by combining the woody core of the industrial hemp plant, known as hemp shiv, with a lime binder. The hemp shiv used is a waste product from other hemp industries, which the hemp plant is grown for. The binder is most commonly a specifically formulated hempcrete binder made using lime and a small proportion of possolans, however a pure lime (strongly hydraulic) binder can be used.
Hempcrete is usually applied on site by spraying or hand casting the hemp lime mix around a structural frame. Most commonly used to create walls, it can also be used for insulated floor slabs, to cast ceilings and roof insulation. Once dry, hempcrete is hard and self supporting, and offers added racking strength. However, it is not structural due to its flexible nature and under excessive weight without the aid of a structural frame would compress. Breathable finishes such as lime or clay plasters and renders can be applied directly to the surface of hempcrete.
Hempcrete is naturally pest-resistant, rodent-proof and has an amazing resistance to fire. It can be used as a new build material, right through to traditional and historic buildings. Because the wet hempcrete can easily be sprayed into the irregular shapes of traditional timber frames, unlike insulations which come in the form of a board or roll, it is fantastic for this kind of work. English Heritage and the Society for the Protection of Ancient Buildings (SPAB) have both highlighted hempcrete as one of the most suitable materials for improving the thermal performance of our architectural heritage.
Hempcrete creates a monolithic wall, re-thinking conventional block and cavity construction, which uses a lot of synthetic materials and unnecessary processes. Even when compared with other timber framed wall systems, a monolithic hempcrete wall sees a reduction in the amount of processes and layers.