Is hemp and lime construction an environmentally friendly choice?

What is hemp and lime?

When lime is mixed with hemp 'shiv' (the inner core of the hemp) it forms a durable, insulating, reworkable and natural cladding material for your home.

As well as stopping heat loss and absorbing sound, it is porous and so is 'breathable' and regulates moisture. A layer of hemp and lime will have a k-value (thermal conductivity) of around 0.1W/m2K - but this varies with the composition and density of the mix. This value makes it similar to straw bale walls in terms of insulation for a given thickness. A timber frame construction could give the same insulation value with a thinner wall, but it would not have the 'thermal mass' that the hemp and lime wall has (the ability to absorb and store heat from both internal and external sources). It will absorb heat when the air around it is hot, and release heat when the air gets cooler, saving energy on heating and cooling and giving a higher degree of thermal comfort.

Is hemp and Lime environmentally friendly?

Lime is has less 'embodied energy' than cement, because it does not need to be heated to such high temperatures during manufacture, and it can reabsorb carbon dioxide over its lifetime.

Although less energy is involved in the manufacture of lime than in cement, it still has quite a high embodied energy. However, in the case of hemp-lime, the growing of the hemp sequesters carbon, offsetting the carbon emissions produced by manufacturing lime.

Hemp is easy to grow, increases local biodiversity and needs little or no fertilisers. Even intensively-grown hemp will sequester carbon, helping to offset that produced in manurfacturing the lime. The microscopic holes in the hemp trap air so the dried hemp and lime mix is an insulator.

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