• 07/11/2018
  • by Ash Dhonsi
  • 0

Hemp for Construction Materials

Much of the hemp grown in the UK in recent decades has been used in the building & construction industry, in a variety of forms, mainly as non-structural building materials and wall insulation. The natural insulating properties and astonishing durability of hemp make it a viable alternative, in terms of technical quality, to traditional materials. Below is a discussion of the technical properties of these hemp building materials, who is making them, notable building projects involving them (in the UK and abroad) and a discussion as to the factors that will see this industry thrive in coming years.

Hemp ‘Concrete’, Pre-Fab Panels and Bricks

Hemp can be used to make building and insulation material by combining the shiv -the woody inner core of the hemp plant- with lime and water, to make a bio-composite with the consistency of porridge. To date, this hemp-lime mixture has been used as a type of concrete; poured into removable wooden shuttering, lightly tamped down (by hand) and dried to produce a 450mm wall cast around a timber frame. This process provides some structural stability as well as insulating benefits and was inventively named ‘Hempcrete’. This natural concrete is highly insulating, lightweight, resistant to pests and mould, has good acoustics and moderates air composition; namely humidity (4). In this form, although fairly strong, it is not suitable for structural, load-bearing walls. This makes the material perfect for the renovation and retrofitting of old buildings to new energy efficiency standards.

The additional benefit of this biocomposite is that it acts as a carbon sink; the hemp plant absorbs CO2 in the growth phase, which is then locked into the material. The material then continues to absorb CO2 throughout its lifetime, pulling more CO2 from the atmosphere, but also increasing the strength of the material.  It is claimed that hemp and lime mixtures of this nature can lock up approximately 110 kg of CO2 per m3 of wall.

How does this compare to current building materials? Concrete manufacturing plants alone contribute 5% of global CO2 emissions, while construction as a whole accounted for only 8% of UK GDP in 2007 (7). Meanwhile, some estimates suggest that buildings account for 50% of the world’s carbon emissions, once manufacturing of materials, construction, operation and heat loss are taken into account (5). Using hemp instead of some concrete or insulation materials could not only make this enormous industry much cleaner, but could also even increase the value of the industry by sourcing hemp materials domestically, rather than importing materials from abroad.

A Canadian study found that, laid in 12 inch thick segments, Hempcrete walls resulted in an R-value of 20, had no toxicity, led to lower energy use and was actually carbon negative – due to carbon being sequestrated into the fibres during the growth phase. Another contributor to this carbon negativity was the fact that you do not heat the Shiv + Lime mixture. With concrete and other traditional materials, you have to heat the mixture to 1,649 degrees centigrade. While cheaper, traditional materials (concrete etc.) have a much more damaging effect on the environment throughout their product life cycle; from raw material extraction, processing and transportation to product use and waste phases.

Here’s a great compilation video and summary of the benefits of hemp materials and their uses around the world: 


One of the issues with Hempcrete is that it takes several weeks to cure, compared to concrete’s few hours, and is prevented from doing so by wet weather. This has led to the development, by Greencore Construction Group in association with the University of Bath, of a faster-drying mix of hemp and lime which is combined with wood fibre to produce 300mm thick prefabricated panels. The major benefit of these new materials is that they are structural (up to three storeys), easy to assemble and retain the vapour-regulating property of hempcrete.

These prefab panels have been used successfully in a number of building projects (see below) to the point where Greencore Construction has begun franchising the technology to small housing developers, the first of which being Ekoetxe; a company from the Basque region of Spain.


In addition to these two building materials (Hempcrete and pre-fab panels), the Scottish firm Industrial Nature is producing hemp bricks using industrial hemp fibres alongside a complex mix of minerals. The resulting material is not only insulating, but is claimed to have an impressive heat absorption/retention capacity. Co-founder Scott Simpson expects production of the bricks, named IndieBlocs, to begin in Leith in April 2018. Currently sourcing hemp from the North of England, the company have secured a pilot crop with a farmer in East Lothian, in an attempt to bring down costs associated with transportation of the raw material. The fibres used are those leftover after high-value fibres for textiles etc. have been removed and sold. It is claimed that a house made from IndieBlocs, which is usually placed around a timber frame, has the potential to save £11,000 in heating costs over 50 years, dependent on energy prices. Industrial Nature have received much support and accreditation for their work, notably from the Edinburgh Centre for Carbon Innovation and Zero Waste Scotland.

Here are some of the benefits of IndiBloc, much of which applies to Hempcrete and the hemp pre-fab panels:


As well as the woody core (shiv) being used for building and insulating walls, hemp fibres can be entwined into loft insulation, resulting in recyclable insulating material that is free from harmful materials and chemicals. The material is antimicrobial, resistant to rotting and, again, carbon fixing. This is in direct contrast to the fibreglass insulation found in most houses which can, granted with a lot of exposure, have a corrosive impact on the skin and lungs (if the fibreglass dust is inhaled).

Hemp Buildings In the UK

In 2009, there was a Hemp Building Symposium hosted in Ireland, by Irish hemp construction expert Steve Allin and Canadian hemp building specialist Jayeson Hendyrsan. Another key player in the hemp building scene has been Ralph Carpenter who, as an architect, built a hempcrete extension to his house in Suffolk. However neither the Irish firm associated with the Hemp Building Symposium nor Ralph Carpenter -of Modece Architects- seem to have much presence online, so it has been difficult to follow the progress being made.

By far the the best known (or most easily traceable) hemp building specialist in the UK has been Ian Pritchett who, in 2012, was running a business turning over £10 million. His projects are varied but include 200 residential houses and 50 commercial buildings. Of particular interest is The Triangle housing development in Swindon.

Approved by the local council in October 2009, The Triangle was a joint collaboration between Kevin McCloud’s development company, Hab Housing, and housing group GreenSquare. The plans, drawn up by Glen Howells Architects, were to create a contemporary interpretation of Swindon’s mid-Victorian railway cottages, using Ian Prichett’s hempcrete building expertise. The idea behind the development was to produce flexible, affordable and efficient housing that would thrive compared to contemporary residential spaces. Dwellings were designed to meet Level 4 of the Code for Sustainable Homes and are ‘future-proofed’ with the fixings, connections and space to allow easy retro-fitting of solar thermal and PV panels at a later date. The development was reportedly delivered with funding from the Homes and Communities Agency.

Work on The Triangle was not completed until July 2011 -one year later than predicted- due to “significant problems with building defects”. These included “things we weren’t expecting from the builder” and “it’s down to the quality of the building works”, the spokesperson for GreenSquare revealed in an article by the BBC (2). This indicates some complexity in working with hemp in construction, although it is not clear whether this comment was in relation to the Hempcrete-casting building method or at Greencore Construction Group’s improved later pre-fab panels. We can only assume the former, as the newly developed pre-fab panels were then successfully used in Hab Housing’s consequent Oxford project, designed by John Pardey Architechts.

In addition to these projects, it is said that Hempcrete has also been used to construct an M&S supermarket somewhere in the UK, and that Adnams brewery have built an “eco-brewery” in Southwold, Suffolk (3). Reportedly, The Science Museum also has an archive store built from hemp.

Hemp Buildings Abroad

While hemp buildings have been fairly sparse in the UK there have, on the contrary, been many more such projects abroad. In 2010, Greg Flavall of Hemp Technologies (New Zealand) famously built a hemp house in Ashville, North Carolina. The finished work had a construction cost of $150 per square foot (sq ft) and was 80% more energy efficient than a similar build using traditional materials. This was due to it having a higher R-value – the unit of measurement used for insulation. This translates to roughly £107 per sq ft, or £1,053.27 per m2; although it is not possible to compare this figure with typical British build costs.

In Canada, where hemp has been legal to grow for commercial purposes since 1998, there has been a more positive and actively progressive approach to the use of hemp from government and industry players alike. This is most evident in the production of hemp for food, but also in the use of hemp in construction materials. The Alternative Village in Manitoba, for example, was a project set up to test and measure the construction process, and resulting performance, of a hemp house.

In the US, meanwhile, the first hemp house was built in 2010 in North Carolina, using crop imported from the UK. It is estimated, by architect Anthony Brenner, that 50 such houses have been built in the US since. The comparatively slow progress in the US can be attributed to the regulatory environment, where industrial farming of hemp was only made possible in 2014. 30 states have since legalised the crop, with 4,000 hectares planted in total in 2016 – the equivalent in raw material for 5,000 small family homes (4). To put this into perspective, Canada grows around 10 times as much hemp as the US, while Europe grows 33,000 hectares, of which France grows the majority.

In fact, one the earliest known examples of hemp architecture is a French bridge built in 500AD. France also exported 30 tonnes (1,000 hemp bales) to Israel for a hemp house completed by Tav Group Architechts in 2016. The firm designed a 250m2 home in the artist’s colony of Ein Hod.

Meanwhile the Netherlands, another big producer of hemp in Europe, exported 500 bales to Taranaki, New Zealand, for a 320m2, £500,000 (NZ $1M) home built on New Zealand’s version of Grand Designs. In Australia, an entire hemp village is under construction off the back the booming hemp industry there, although they too were importing hemp from Europe to begin with.

The Bottom Line: Why Isn’t Hemp Housing Happening On A Large Scale?

Inevitably, and as with many environmentally friendly alternatives, hemp, whether used as Hempcrete, prefab panels or IndieBlocs, is more expensive than current materials. This is the only barrier to it being used on a much bigger, countrywide scale. The question then, is what factors drive the high cost? And; what is the scope for these factors to be feasibly reduced to a point where hemp can be price-competitive with current materials?


First and foremost, there is the opportunity presented by the thermal properties of hemp building materials. As we have established, hemp building materials have much better thermal properties than existing materials. This means that hemp houses will save the occupier money, in the form of heating cost savings, long into the future – until the house is no longer habitable. As seen above, these savings are fairly significant; £11,000 over a 50 year period. Factoring these savings in at the design phase helps to increase the price competitiveness of hemp against current materials; pay more for hemp now and you’ll save money over time, whilst also having a positive impact on the environment in the meantime.

It follows, then, that any increase in the price of energy (heating costs) will add to this money-saving effect. A briefing paper for the House of Commons suggests that gas prices (for cooking, heating etc.) have increased by around 40% in the 27 years from privatisation of the industry in 1987 to 2017. The main price hike began in 2005, leading to a roughly 120% increase in the 12 years to 2017 (6). If we see even an 80% increase in prices over the next 50 years, the savings to be made jump to £19,800.

While this figure of savings between £11,000 – £19,800+ over 50 years, dependent on energy prices, adds strength to the ‘business case’ for using hemp in construction, the returns are more difficult to translate in practice. It is difficult to sell a property at high above the market average on the grounds of future returns which, as we have found, are dependent on future energy prices and thus can only be estimated. It is possible even that energy prices drop, leading to no return at all. Indeed this was one of the problems with Kevin McCloud’s development at The Triangle; contrary to the desires of the design team, the finished houses were not affordable in a like-for-like comparison with other local housing stock.

In essence, the view that a large saving now is preferable to the -fairly likely- possibility of an equal or even larger saving over the next 50 years, is holding hemp back. What this view fails to account for, however, is the value of the environment. Many forget that investing in environmental protection and environmentally friendly procedures can provide returns in the form of clean air, biodiversity, beautiful landscapes etc. – things that are much more difficult to put a price tag on than heating bills.


Another way to increase the competitiveness of hemp is to lower the cost of production. This can be done by identifying which parts of the country have the potential to be most productive, when farming hemp, and encouraging farmers to grow hemp in those areas. Another production-side factor is the proximity of hemp farms to a processing plant and the proximity of the plant to commercial customers. Transportation of heavy hemp bales to the processing plant is expensive; reducing this distance will help to lower costs. As we have seen, there are already companies in the UK streamlining their operations and producing technically impressive materials at a workable price. More interaction between growers is the only way that production costs can be brought down. If you are interested in connecting with other hemp growers or processing companies, join our Facebook group here to begin networking today.


Another way of increasing the competitiveness of hemp compared to current materials is to make the costs, or ‘externalities’, of the current materials more clear. For example, putting a price on global warming from human-induced CO2 might make CO2 intensive products, like concrete, more expensive and less attractive. A carbon tax is one way that this can, and is, being implemented. Carbon negative products like hemp building materials would attract no tax -and may even receive subsidy!- making them cheaper and more attractive.

Equally, the reverse process also works… Rather than indicating how bad and damaging traditional materials are, efforts could be made to show the benefits, both financial and otherwise, of using hemp. For example, hemp houses ‘breathe’ and regulate airflows better, thus providing inhabitants with cleaner air. This, in turn, has not only be found to make people more productive, meaning you can work harder for longer and earn more money (see Google’s research into this), but may also reduce the number of respiratory problems had by inhabitants, thus resulting in fewer visits to the GP and, consequently, money saved in the NHS. Similarly, building a domestic supply of building materials will reduce our dependence on imports, and will inevitably bring more stability and independence to our economy.

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