Why Build With Hemp?

February 11, 2020

What is Hempcrete?

 Hempcrete is a composite building material made by combining small pieces of hemp hurd processed from the woody stem of the industrial hemp plant (cannabis sativa) with a lime-based binder. Hempcrete walls are wet-mixed and constructed on-site around a structural, load-bearing timber frame to form monolithic, lightweight, self-supporting walls.  In the hemp-masonry homes built by Hemp Homes Australia, hempcrete is used to construct all the external walls and, depending on the client, at least some of the internal walls. The external walls are protected with two coats of lime-based organic render and the internal walls are either finished with non-toxic clay plaster or simply left as natural walls.

When the lime-based binder in hempcrete is mixed with water and organic components such as hemp hurd, the composite material hardens into a self-supporting mass. Over time, the lime petrifies the organic material within the wall, which continue to harden as it ages, eventually becoming a comparatively light-weight solid stone-like wall. 

Hemp hurd is a sustainable, organic material derived from processing the woody stem of the industrial hemp plant (cannabis sativa). Until very recently, the hurd required to build our hemp-masonry homes had to be imported into Western Australia from overseas or interstate. However, with the recent establishment of both a Hemp Processing Plant in Margaret River and the pioneering of Industrial hemp fibre crops in the local area, we can now proudly claim to be building the only, locally grown, and processed hemp-masonry homes in Western Australia.    

Hempcrete not only creates enviably healthier living spaces, as a building material, its environmental integrity puts it in a class all its own.

What gives our hemp homes a five-star health rating?

Hempcrete walls, along with their lime and clay-based finishes, are vapour-permeable and are often described as “breathable” or hydroscopic. When humidity levels inside the home are high, hempcrete walls take in water vapour, and then release it when humidity levels drop, passively regulating humidity within the home. In our hemp homes, the hempcrete walls usually make the installation of ventilation fans in highly humid bathroom spaces redundant. This “breathability” ensures any build-up of condensation or moisture on the walls is avoided, circumventing potential problems caused by dampness and mould, factors long associated with various health issues. Dampness and mould in buildings can also result in fundamental long-term structural damage to the buildings themselves. Hempcrete’s capacity to natural regulate the internal humidity of a building provides a consistently comfortable and healthy living environment, contributing to the long-term well-being of both the home’s occupants and the building itself.

The combination of the hemp hurd and lime in hempcrete acts a highly effective natural resistance to pests, making it unnecessary to add any toxic chemicals or additives to the building structure.  The use of lime and clay renders, coloured only with natural oxides, also removes the need to utilise any finishes containing volatile organic compounds (VOCs) or other potential allergens, a fact that is highly appealing to many health-conscious owners.  The lack of toxic building materials on a hempcrete site also ensures a much healthier working environment for our builders and tradespeople.

Energy Efficiency

Without doubt, the savings in energy costs guaranteed by building with hempcrete walls is a big incentive for our clients.   Hempcrete walls have the distinctive capacity to provide both thermal mass and insulation.  Warm air, passively heated by the sun, or from a heat source within the home, is trapped between the small pieces of hurd-lime composite in the walls and within the microscopic pores of the hurd itself, ensuring all external and internal walls act as highly effective, natural heat stores.   The passive thermal heat trapped in these 300 mm thick walls can then be released slowly when the building cools down.  Additionally, the tiny air pockets in the walls’ composite material act as natural insulators, effectively protecting the home from external heat or cold. The thermal mass and insulative capability of hempcrete walls work together to naturally regulate temperature fluctuations and maintain internal temperatures at a comfortable level with very little use of conventional heating or cooling systems. 

According to the owner of a house near Margaret River we completed in 2018, even during winter, the temperature inside the home in the mornings, without heating, is around 17 - 18 degrees. In very hot summer weather, the internal temperature never goes higher than a maximum of 25 degrees and will quickly cool down with a slight sea breeze.  In colder months, given some winter sunshine, the internal temperature sits around 20-22 degrees during the day.  In this particular home, sufficient cooling is provided by the occasional use of an overhead fan in the living area and natural cross ventilation through window openings.  In winter, a small, efficient wood burning heater, which according to the owners is often used more for aesthetics than need, provides ample additional heating for the whole house.  Although this particular home was given an official energy rating of 7.1, the home’s architect believes this rating may not fully account for the actual insulative capacity of the internal and external hempcrete walls because hempcrete is still a relatively unknown building material in Australia.  Evidence based on readings from internal and external thermometers over the past year indicate this home is performing much better than its official rating.  In any case, there is no doubt that hempcrete’s thermal and insulative performance will ensure the owners enjoy considerable savings in energy costs all year round for the lifetime of the home.  

Sound absorption and high-level acoustic performance:

Owners of our homes are also always pleasantly surprised by the substantial sound absorbing and sound insulating capabilities of their homes. According to owners, rain and wind noise during severe winter storms barely registers inside their houses, while the solidness of the building structure guarantees little to no perceptible movement in any part of the home.  Noise from everyday sounds is ostensibly absorbed by the walls, creating a real sense of tranquillity and peace inside the home.

As hempcrete has been used overseas in the construction of music studios, the owners of one home, who are self-described “music buffs”, were keen to test their high-quality stereo equipment in the home.  According to these owners, listening to music in this home through their stereo system is “like sitting in front of an orchestra; it is a really full sound and we have been able to hear individual instrumental sounds that we have not been able to hear in other home environments.” It seems that the porous nature and lower density of the composite material in the hempcrete walls maximises sound absorption, resulting in an ideal listening experience.

How does growing hemp help the environment?

Industrial hemp is NOT marijuana. It comes from the same Cannabis Sativa plant but is a distinctly different variety with almost nil levels of THC, the psychoactive component in marijuana. It is now being grown commercially for seed and fibre in many parts of Australia and, as several local South-West farmers have shown, it grows exceptionally well as a biomass crop in this region. Much is claimed about the environmental positives of this “wonder plant”. Rather than add to this hyperbole, let’s simply look at what we can learn from the local hemp biomass crops grown  and harvested recently for our sister company, (and the supplier of the hurd for our hempcrete), Margaret River Hemp Processing.  

  • Industrial hemp grows REALLY fast! In 2020 crops reached heights of 5-6 metres in about seven months and yielded an average of 10+ tonnes of dry biomass per hectare. Growth of that much biomass needs a lot of photosynthesised carbon! Hemp is undoubtedly one of the best CO2-to-biomass conversion crops there is and considerably more efficient than Agro-forestry at sucking up atmospheric carbon.
  • Above ground crop biomass of this size and quantity promotes vast networks of subsurface plant structure and root exudates which along with significant quantities of fallen leaves, flowers and stems feeds a plethora of soil biota, adds carbon and nutrients, and protects, binds and improves soil structure. Hemp is not only a sustainable crop but, as a rotational crop in local farming systems, it has the capacity to significantly add to the value of the land it is grown on. 

Most residential building sites generate considerable quantities of waste material.  However, the organic nature of hempcrete, lime-based renders and clay plasters results in considerably less waste being generated during the building process as these materials can be simply washed away or dug into the ground. 

Lifespan of Hempcrete

A properly constructed hempcrete wall will become harder as it ages. The lime-hurd composite material forming the hempcrete walls also helps preserve the encased timber structural frame within, further ensuring the longevity of the building structure.

As hempcrete, lime-based renders and clay plaster are all vapour-permeable, provided sound construction principles are fully adhered to, there should never be any damage or weakness to the building structure from mould or dampness.  Hempcrete is also naturally insect (including termites) and rodent repellent ensuring negligible future problems from these sources.  

Hempcrete is also known to be highly fire retardant, making it a potentially viable building material for fire risk areas.  To prove this point, Gary, the director of Hemp Homes Australia, placed a sizeable brick he had made out of hempcrete into the centre of a roaring bonfire and left it there for many hours until the fire had died out.  The brick was retrieved from the ashes intact, with little perceptible damage.

To Conclude:

Hempcrete homes are unique, highly aesthetically-pleasing and offer a myriad of health and life-style enhancing features. Owners of hempcrete homes can be confident that their home has been built, and can be maintained, with considerably less impact on the environment than conventional builds. Sustainable and timeless, hempcrete is a building material for a better future.  

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