What is Hempcrete?

Hempcrete, or “hemp-lime”, is a medium density natural insulation material produced by wet-mixing hemp shiv with a lime binder, which has extraordinary thermal properties and “deep-green” sustainability credentials. Because of its lime binder, hempcrete provides thermal mass as well as insulation, and the two work together to produce a superior thermal performance. Changing the ratio of lime binder to hemp varies the strength and thermal properties of the hempcrete allowing it to be used as breathable insulation in a solid floor, walls or roof. It can be used in new build and in renovation projects.

Hempcrete creates healthy buildings, due to its ability to absorb and release moisture vapour from the interior air (hygroscopicity). This helps to passively regulate internal humidity and prevents condensation and damp which can lead to toxic or black mould growth. Hempcrete and the finishes applied to it are “breathable” (vapour-permeable) which increases the longevity, and maximises the thermal performance, of the building’s fabric. This property makes it particularly suitable for use in historic or traditional buildings where it works in harmony with the other materials in the building, preventing moisture from building up in the building’s fabric.

In new build, Hempcrete is cast around a structural frame (usually a timber frame), and is either “hand-placed” into temporary form-work or spray applied. It is then left to dry for several weeks, after which time a variety of finishes can be applied. The usual finish is a lime/clay plaster or a lime render, but timber or masonry cladding can also be used.

Hempcrete is unique in its ability to provide excellent thermal and acoustic properties in a single structurally sound, airtight building material which can be used to form the whole thermal envelope of a building. Other modern construction methods require the use of several different materials, products and assemblies to match hempcrete’s properties and meet the many different requirements for walls, floors and roofs.

Costs

The costs of building with hempcrete are comparable to those of conventional construction and in many cases, due to it weighing less than masonry and requiring less substantial foundations, hempcrete has been a more cost effective alternative.

Advantages of using hempcrete:

  • Hempcrete is highly insulating and airtight; ideal for meeting today’s building standards.
  • Hempcrete also has thermal mass. This means that hempcrete buildings change temperature more slowly and thus have reduced energy demands for heating and cooling compared to buildings insulated with lightweight insulation materials.
  • In hempcrete, insulation and thermal mass work together resulting in an extremely energy efficient building,
  • Hempcrete is natural, vapour permeable and hygroscopic, creating healthy indoor environments, and protecting the building’s fabric.
  • Hempcrete materials are produced locally; with UK grown hemp, and binders from the UK or Western Europe.
  • Hemp transforms CO2 during its growth by capturing carbon and releasing oxygen. Using hemp in construction locks away carbon for the lifetime of the building. Research indicates that a net 110-165kg of CO2 is sequestered per cubic metre of hempcrete.
  • Hemp can be grown in rotation with food crops to improve the soil and reduce weeds, it does not require agrochemicals in its cultivation and there is no need for pesticides or insecticides.
  • The hemp shiv used in hempcrete is a low-value waste product of the hemp seed and fibre industry.