People usually choose natural materials because they want a building that is sustain­able or ‘low impact’ in terms of eliminating or minim­izing any lasting negative effect on the world in which we live. In practice this means reducing as far as possible the ‘embodied energy’ associated with the materials and methods used in the construc­tion of the building; minimizing the amount of fossil fuels needed by the occupants to power, heat and cool the building through its lifetime; and minimizing toxic emiss­ions and any other harm to human society or the natural world.

People also choose natural materials because they are increasingly aware of how such materials can not only maintain the structural fabric of the building well but also help to keep humans in good health. In contrast to many synthetic materials, natural materials contain no harmful chemicals. They are also vapour permeable (they allow moisture to pass through), which has significant implications for the health of both the building and its occupants.

There are many natural materials available for use in construction: timber, stone, earth, animal hair, straw, hemp, lime, reed and fired clay, to name just some. Many of these materials can be used in more than one way. They have a long pedigree of use over centuries, or even millennia, by humans (and other animals!) to provide warmth and shelter. Today, with our growing awareness of the threats associated with over-dependence on fossil fuels, and our increasing understanding of the negative side-effects of synthetic building materials mass-produced by highly industrialized processes, has come a resurgence of interest in older and more natural materials and methods for construction.
Hempcrete (a hemp–lime composite construction material) is one such new material. Comprising the chopped stalk of the industrial hemp plant mixed with a lime-based binder, hempcrete provides a natural, healthy, sustainable, local, low-embodied-energy building material that can truly claim to be better than zero carbon. Carbon dioxide taken up by the plant when it was growing is locked up in its woody fibres, and at the end of the building’s life the hempcrete can be left to compost and be used as a soil additive rather than going into landfill. As a highly insulating material with significant thermal mass, hempcrete has excellent thermal performance within the structure of a building, and there is increasing evidence that it actually performs much better in real-life situations than is suggested by steady-state modelling.

Hempcrete is especially attractive to self-builders and community groups, because of the relatively low-tech nature of the construction method. Also, owing to the fact that it’s a relatively labour-intensive construction method, big savings can be made by providing your own labour. However, as our company and others have proved over recent years, hempcrete is also commercially viable as a construction material in a wide range of applications. Its cost is comparable to that of conventional construction methods, but if you factor in the true cost of the embodied carbon of conventional building materials, in terms of environ­mental damage, and consider the financial benefits of the energy savings that hempcrete delivers through the lifetime of the building, you could argue that it’s actually a lot cheaper!

There is a great pleasure to be found in building with hempcrete, which comes not only from the extraordinary thermal performance achieved but also from the simplicity: both of the material itself and of the elements within a typical hempcrete construction. Hempcrete’s low-tech nature means that, with relative ease, highly energy-efficient buildings can be constructed that contain virtually no synthetic, highly processed or high-embodied-carbon materials. With a good understanding of the material, and a little practice, hempcrete is a hugely rewarding material to work with, and can produce beautiful, healthy, ‘future-proof’ buildings.

Excerpt from William Stanwix’s and Alex Sparrow’s The Hempcrete Book