Insulation*: Hempcrete

WHAT IS IT?

Hemp, an industrial variety of the cannabis plant family, is farmed and harvested in the UK. It is one of the fastest growing crops, sequestering carbon as it grows. Its extracts are used to create many products, including oils, fabrics, insulation, paper, bioplastics and others.¹ The inner, woodier part of the hemp plant's stem, called the 'hurd' or 'shiv', is extracted as a core ingredient in making Hempcrete.

The hemp hurd / shiv is mixed with a binder, either lime or cement to create Hempcrete. "Hempcrete can be wet-mixed on site and cast around a structural frame, or pre-cast off site to form blocks or panels."²

Hempcrete vs Hemp Wool

Hempcrete is a building insulation system* that acts as a buildings' main envelope, whereas Hemp Wool acts as a one-to-one replacement for conventional insulation products.

Click to see Hemp Wool

Cross section of Hemp Stalk - Source

MATERIAL LIFE CYCLE

Source

KEY INFORMATION:

Is manufactured and available in the UK.
Contains British hemp
Can be used as walls, roofs, ceilings and floors.
Can be cast-in-situ, sprayed-on, pre-cast blocks or prefabricated panels.
Wall thickness is 300-350mm which achieves a U-value of around 0.2 W/m2K at 300mm to 0.17 W/m2K at 350mm.⁵
Requires a masonry plinth of at least 250mm from the ground (protects hempcrete from groundwater and splashback) ⁵
Highly breathable and hygroscopic, controlling indoor humidity by absorbing condensation.⁴
Naturally fire, mould and pest-resistant.⁴
Hempcrete installed in suitable thicknesses not only has insulating properties, but also thermal mass. It significantly outperforms other insulation materials that do not have thermal storage capabilities.⁴
High sound absorption
Hemp can be grown in 3 months and is compostable. In some climates, two or three hemp crops can be grown each year. At the end of it’s useful life, hempcrete can be mixed into the soil as a biologic and mineral amendment.⁴
Regulates internal temperature, being stable at 16 -18°C all year round, whether it’s +30°C outside or -10°C, which lowers operational cost of building.⁶
Self-building with hempcrete can lead to substantial cost savings, as its low-tech installation allows builders to participate directly, especially with accessible training for hands-on involvement.⁶
Durability: Low risk of cracking and can withstand seismic activity. Requires minimal maintenance.⁷ Lifespan of 300-500 years.⁸
Requires a breathable render (lime), plaster or membrane to ensure air-tightness.
Hempcrete is malleable before it is dried, it can be molded, cut into, or carved in. Fixings can also be hammered/drilled into hempcrete even after it is dried.

Challenges with building with Hempcrete

How much does building with Hempcrete cost?

Due to many factors including labour, bespoke design and material sourcing, there is no replicable answer to this. It might be slightly more expensive or slightly cheaper, but one must account for the savings in the building's operational costs due to Hempcrete's efficient properties. You can view the varying costs of Hempcrete Blocks here.

Built Examples using Hempcrete