Is hempcrete better than concrete?
It depends what you mean by ‘better’, as the two materials are good at different jobs. Whilst the name can be misleading, it is worth noting that hempcrete and concrete are very different materials and are not used in the same way. The term ‘hempcrete’ is often used because historically it has been mixed and cast on site into a shuttered framework, in a similar way to concrete. Concrete uses a binder of cement and an aggregate of sand mixed with other larger materials like gravel, stone or rubble. In comparison, hempcrete uses a lime-based binder and the hemp shiv is the aggregate.
Hempcrete (in its usual “hemp-lime” form) has been developed as a non-structural material. Therefore, it cannot replace concrete for structural applications. Also, due to the plant-based aggregate in the material, hempcrete does not perform well in locations where it is exposed to standing water, or constantly has water running across it. Therefore unlike concrete, it cannot be used in below ground or foundation applications.
Whilst concrete is good at keeping water out, it can also trap moisture inside the building, meaning that it relies heavily on mechanical ventilation systems to purge moisture from the interior. Hempcrete is vapour-permeable and hygroscopic, which means it can absorb and release moisture in response to the internal environment. This means humidity levels are naturally regulated and ventilation systems, if required, can be a lower spec and allow cost savings.
Whilst hempcrete and concrete both act as heat stores due to their thermal mass, hempcrete also has far superior insulation properties. Whilst concrete has been receiving a lot of bad press recently due to its enormous carbon emissions, hempcrete actually sequesters more carbon than it emits (as outlined above) so is actually having a net positive impact on the levels of atmospheric carbon.
In comparison to conventional concrete cavity systems, hempcrete is generally a simpler construction with simply a structural frame, the hempcrete and the finishes. This makes it more accessible to self-builders and can save time and money in construction.