Associate, John Read, looks at the merits of hempcrete and why understanding the product is so important.
Hempcrete has got a lot going for it. It’s a sustainable material with excellent eco-credentials and is gaining increasing popularity in construction.
What is it?
Hempcrete is the popular name for a composite building material made by mixing the stem (shiv) of the hemp plant with a lime-based binder. The hemp has a high silica content which allows it to bind well with the lime.
In construction, it can be used instead of concrete in the formation of walls, floor slabs and ceilings. It can also be used as an insulator in roofs.
Non-load bearing, it is often used in conjunction with a structural (load bearing) timber frame in new dwellings
Why is it becoming popular?
Hempcrete is incredibly eco-friendly. Its capacity to absorb carbon makes it more eco-efficient than manufactured zero-carbon materials. Carbon is taken up as the hemp grows and stays within the plant when it is processed into hempcrete. Hemp locks away more CO2 in its growing phase than is used when making it into hempcrete.
As a significant amount of air is trapped within the hempcrete it is both a breathable and self-insulating material.
Advantages for homeowners:
- It’s extremely energy efficient.
- It maintains a stable temperature.
- It’s a breathable material.
- It provides a healthy environment.
For designers and contractors, its inherent properties are very useful:
- It’s hygroscopic, so absorbs moisture and humidity within a building
- Its strength increases over time
- It doesn’t shrink, so cracking is reduced.
- It can be applied as a spray or plaster
- It can be used seamlessly around a building to create an airtight layer
What can go wrong?
Hempcrete doesn’t behave in the same way as more common building materials and problems can arise from a lack of understanding of the material and its proper application. Designers and contractors need appropriate training in its use for construction and detailing.
In several recent surveys of buildings containing hempcrete, we’ve observed problems that clearly demonstrate a lack of understanding of its properties – its breathability and appropriate treatment of moisture. This lack of understanding has resulted in the associated use of materials that trap moisture within walls rather than allowing free passage – which would be appropriate with hempcrete.
Furthermore, proper detailing is key. Our surveys have identified poor detailing at window and door openings which gives rise to cold bridging and air tightness issues.
Read a recent case study to find out more.