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The Hemp House

Open House at the Hemp House which was extremely popular during Architecture Week

Move over Haybales and Mudbrick, there’s a new bio -building material making its way to a construction site near you.  

The Hemp House is another place I visited during Architecture Week. From the outside it's an attractive,  normal looking dwelling, built over two levels and overlooking a beautiful sloping garden. On the inside however, you can see that some of the unrendered walls are made of a softly textured material not unlike fine cereal or light -coloured wood chips. That material is Hemp hurd, the residue of specially grown hemp.

This recently rediscovered material which uses only hydraulic lime and water and using new technology, has led to Hemp Houses being built in several countries including France, the USA and Australia. For a quick rundown of the process and building techniques click here.

The Advantages of Hemp

According to  discussions at the Hemp House with Andi Lucas, Hemp Mill Owner and President of  the Tasmanian Hemp Association, Greencamp and other sources as indicated in the links, Hemp does have several advantages.

(L-R) Sharron,one of the Guides and Hemp House owner, Becky

1.     Has the potential to become a low -cost sustainable product which could help to alleviate our housing shortages. However, growing any kind of Hemp is not legal in this state and while there are a few experimental crops, there is nowhere near enough material for home building, which means that those which are, are both expensive and comparatively rare. There are also still very few architects and builders who know how to work with this material.

2.       Has excellent thermal properties and requires practically no heating or cooling

3.       Is fire, mould and termite resistant, humidity regulating and a non – toxic, breathable material 

4.    Carbon negative. One of the benefits of hemp as a building material is that it absorbs four times more carbon than trees. According to Ana Vasio’s article for Greencamp, 1 cubic metre of hemp can hold up to 40 kgs of carbon.  
Concrete making by contrast, remains one our most emission intensive industries, producing around 8% of the world’s CO2. Some materials used in concrete -making such as the right kind of sand, are also in short supply while steel making, though used for many  purposes besides construction, contributes 11% to the World’s carbon emissions. 

Crowds gather in the kitchen to listen to Andi talk about the merits of Hemp and the challenges preventing greater uptake for home building
Hempcrete - the material which is used for building - requires only three simple ingredients - hydraulic lime, water and milled hemp - but also patience and much labour

6.       Sustainability. Although trees are regarded as a renewable crop, they take a long time to grow and release stored carbon when cut. By contrast, Hemp can be grown as an annual crop and what is used in building is usually a byproduct of its use in industrial processes, or for high value products such as medicinal oils, edible seeds, biofuels and fibres for clothing or insulation. In future it may even be used instead of graphene in capacitors or in batteries instead of lithium. In the days of of sailing ships vast quantities of hemp were grown for rope and sails. Hemp can be grown on any type of soil and doesn’t need fertilisers or pesticides to grow. 

7.       Durability. It is early days as far as modern hempcrete houses are concerned but if the 6th Century Hemp Bridge in France is any guide, well -constructed and well -maintained, hemp houses should grow stronger as they age and could last for hundreds of years. In modern times, France began to use Hemp to replace wattle and daub in restoring half - timbered houses. Even when Hemp houses are finally demolished, the material in them can be recycled and any remains are fully biodegradable and leave no toxic residue behind.

A calm, warm and breathable bedroom. The walls have been left natural

The Challenges 

So why isn’t everyone building with Hemp? While Hemp hurd can be used for roofs, walls and floors, it doesn’t have the load -bearing strength of traditional materials, so framing must generally still be done using wood or steel. However,  this is changing (see the exceptions below), and it is still far less than in conventional construction.
 Cost remains a barrier while production volumes and supplies remain small. There are also still few experienced architects and builders to take on such projects and the labour -intensive nature of on -site mixing and construction means that it still costs 20 - 30% more to build with Hemp. However, many of these things could change as hemp becomes more popular for all sorts of reasons and pre -fabrication comes into the field. See for example the Lego -style blocks which lock together and provide additional structural strength as well as not needing long periods of drying time. See also the Flat House in the UK constructed of pre- formed panels and completed in just two days.

Although the Hemp used in construction is not the mind -altering kind and has less than 0.3% THC -  the active ingredient in cannabis, which has around 15%, its association with drug use has tarnished its reputation and keeps it illegal in many states. Governments and local councils are still very conservative about new materials, especially one as controversial as Hemp. They may also be heavily influenced by existing building industry players. As far as growing hemp goes Hemp has difficulty competing with other crops when many of them are subsidised, as you’ll see in the following clips.

One thing is certain. We'll be hearing a lot more about Hemp in the future and not just in home building.

For more examples of Hemp Houses, click here.