Understanding the Thermal Performance of Hempcrete
Hempcrete has garnered significant attention in sustainable construction due to its remarkable thermal properties. As a bio-composite material made from the woody core of the hemp plant mixed with a lime-based binder, hempcrete offers insulation primarily through the air pockets trapped within the material. These air pockets exist both in the spaces between the particles of hemp shiv and within the microscopic pores of the shiv itself, contributing to its thermal efficiency.
Thermal Conductivity and U-Values
The thermal conductivity of hempcrete is notably low, typically ranging from 0.06 to 0.07 W/mK, as verified by solid-state lab testing conducted by binder manufacturers. This low thermal conductivity makes hempcrete an effective insulator, allowing it to retain heat in colder conditions and keep interiors cool during warmer periods.
In terms of U-values, which measure the rate of heat transfer through a material, hempcrete performs impressively well. For new build projects, the typical thickness of hempcrete walls ranges from 300mm to 400mm, providing the following U-values:
- 300mm Thickness: 0.2 W/m²K
- 350mm Thickness: 0.17 W/m²K
- 400mm Thickness: 0.15 W/m²K
These values indicate that hempcrete can meet or exceed the insulation requirements for many modern buildings, contributing to lower energy costs and a more comfortable indoor environment.
Factors Affecting U-Value
When using hempcrete as a cast-on-site material, whether hand-placed or spray-applied, the U-value achieved can vary. Factors such as wall thickness, the type of binder used, the exact specification, application techniques, and the skill of the contractor all play a role in determining the final thermal performance of the structure.
However, it’s crucial to understand that with hempcrete, the thermal performance is not solely about the U-value. The material’s ability to regulate indoor temperatures, maintain breathable walls, and contribute to a healthy indoor climate are equally important aspects of its overall effectiveness as an insulating material.
For more detailed information on hempcrete and its applications, visit UK Hempcrete.
