On Hemp as a Natural Building Material

By Matt Muldoon

Hemp is an incredibly versatile construction material. A non-psychoactive member of the cannabis family, it has been cultivated around the world for at least 10,000 years. It grows voraciously, and requires no herbicides and little or no pesticides. The fibres of the plant have long been used for rope, textiles and paper, but now are also used for insulation, hempcrete, board and even roofing tiles.

Hempcrete is an exciting material that can be used as an alternative to concrete and a lot more besides. The fibres of the plant are mixed with lime to create a substance which hardens like concrete. Unlike concrete however, it is a good insulator and also breathable and very lightweight (500kg/m3). This means it can be used for walling, either cast around a wooden frame or in hempcrete blocks. It can also be used for floors, roofs and foundations.

A hempcrete building offers a healthy, pleasant environment. The hempcrete itself insulates effectively (if you’re interested: u-value for 300mm hempcrete = 0.25W/m2K.); and, as a breathable material it regulates humidity levels well, avoiding dampness and condensation problems. Since it is breathable, hempcrete would normally be finished with a lime render/plaster.

As an eco-material, hempcrete’s credentials are rock-solid, sequestering around 110kg of CO2 per m3. Hemp is a crop which can be cultivated throughout much of the habitable world, and lime production requires 80% less energy than cement production.

Hemp fibres can be used as insulation, offering a natural alternative to synthetic materials with a high embodied energy. And the fibres can also be sandwiched to make an alternative to fibreboard or wallboard.

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By Matt Muldoon of the Natural Building Company

On NBM – Introduction here

On Earth as a NBM here

On Straw as a NBM here

On Lime as a NBM here

On Turf as a NBM here

To check Matt Muldoon and his company out, click here.

Read our article on him and TNBC here.