What is Hempcrete?
Hempcrete is used as a monolithic wall, floor and/or ceiling material. It's a high performance insulator and can be finished to suit both modern or period homes. It is an eminently carbon negative, natural and lightweight construction material which provides highly efficient temperature and moisture control among other unique characteristics; it is formable, dynamic, cures within hours and is one-seventh the weight of concrete.
Highly fire resistant
Prevents mold & rising damp
No dry rot
Preserves the timber house frame
Complete thermal envelope
Negative carbon footprint
Non-Toxic: No VOC’s (Volatile organic compounds)
Absorbs sound/high acoustic performance
Why is hempcrete so special?
The growing popularity of hempcrete is based on the fact that it holds a unique position as a building material, combining the qualities of thermal mass and insulation. It has thermal mass (think concrete, bricks or hot water bottle) to maintain stable temperature, bank up internal heat and shield from harsh summer sun. Interestingly, it's also insulative due to its porous, airy, fibrous composition, reducing heat transfer and loss. These two properties work in tandem to outperform most current day wall systems whilst remaining low-tech, ecological and easy to install. Reducing electricity usage and dependence on air conditioning by tremendous margins. Its promise and interest are continually demonstrated in an ever growing raft of studies.
Hempcrete also has specific breathability properties, actively absorbing and diffusing vapour throughout its large mass. This is vitally important because there is a common misconception that temperature is the gold standard for warmth or comfort, whilst ignoring the dramatic effect of moisture content in your home. You become colder faster when moisture is present. Ever notice how quickly you freeze after leaving the pool?
Or when you’re sweating and enter an air-conditioned room, think about how quickly you become cold. Ever notice how cold you are after a shower before drying off. The more moisture, the quicker heat conducts from you. In fact, the reason your body sweats (creates moisture) is to remove excess heat from the body.
One of the gifts of Hempcrete to the industry is its strong moisture regulation and moisture buffering abilities. It protects from the moisture spikes which modern houses are known for. Creating healthy, comfortable and stable temperatured homes.
Hempcrete balances internal enclosures to a relative humidity of between 40% to 60%, the range within which humans have evolved to find comfort. We interpret spaces with stable humidity as ‘comfortable’, whereas rooms with too much moisture as ‘stuffy’ or ‘damp’
Hempcrete strength is its simplicity, or because of what it is not. A standard Australian wall can include a brick veneer, insulation, sisilation, a damp proof membrane plus external cladding; all aspects which can fail, are co-dependent and have varied lifespans. The simplicity of Hempcrete is that it can perform the duties of all these materials as a single monolithic system. Plus Hempcrete being airtight, solid and devoid of wall draughts. This is hugely important because complete thermal envelope of the house is created. Its continuity diminishes thermal bridging, probably the largest contributing factor to heat entry and exit. What is thermal bridging? See below here
How Environmentally friendly is it?
“One cubic metre of hempcrete will sequester approximately 110kg of carbon from the atmosphere. An average sized house would be built using around 50 cubic metres of hempcrete for the walls, meaning that an average hempcrete house would lock up 5.5 tonnes of carbon for the lifetime of the building. This compares to a more standard new house of a similar size, in which the walls would be likely to emit 48 tonnes of carbon into the atmosphere (M. Berners-Lee 2010). This is a saving of 53.5 tonnes of carbon for every house built.”
Graham Durrant - “The Long Version - Hemp-Lime Spray.” Hemp, 8 June 2019 hemplimespray.co.uk/why-we-should-build-with-hempcrete-2/
What is thermal bridging, why is it important and what does it have to do with Hempcrete?
When an object has a lower insulative capability or a higher thermal conductivity than its surrounding materials, heat energy will pinpoint the area and flow through rapidly. This is known as thermal bridging. It can occur wherever there is a gap in insulation, and in a standard house this happens easily and often. Expensive conditioned air escapes where the timber house frame interrupts the insulation. It also occurs, for instance, at voids for power-points, every stud, empty eaves, the space between windows and the stud frame, wall corners where studwork meet, small missing portions of insulation installation due to a hungover apprentice or weight bearing lintels above windows and doors; Basically anywhere where insulation isn't.
The reason why we want to avoid this phenomena in Australia is often because of unwanted heat, which simply flows in through these points. This is one of the major reasons for the performance-gap between what the architect estimated and the reality an cost of conditioning the finished house.
Thermal bridging can only occur at points with insufficient space/buffering/insulation. This is why hempcrete can perform so well as it creates a complete insulative envelope. You’re creating a monolithic wall of continuous insulation with no potential for easy and rapid heat loss or entry.
Why is Hempcrete's thermal Mass Important?
Materials with thermal mass have the capacity to absorb, bank and release heat energy at a later point when the surrounding air temperature changes. Some examples; the Italians use marble to keep a cool thermal bank inside the home to cope with the hot Mediterranean sun. In the southern US, rammed earth shields from the scorching heat. Cob and clay homes proliferate India and Africa (Which predate, but are similar to, carbon intensive concrete). Here, in Australia, we envy those with the classic and stable mudbrick or bluestone homes which bank up the cool. These are classic temperature regulation or dampening techniques for climates with a high diurnal temperature swing.
Hempcrete, being thermally massive, provides a serious alternative to modern, high insulation, highly air conditioned and energy hungry housing which lack thermal mass. It also allows us to hop off of the merry-go-round of housing industry consumerism with patented, aggressively marketed 'environmental' building materials which take more energy to create than they'll ever save. Additionally, flimsy modern houses also require our vigilant attention to keep windows and doors closed to preserve our precious expensive freshly conditioned air. In other words, only the air is conditioned, nothing is there to bank it up. With the temperature stabilised by a Hempcrete homes thermal mass, energy absorbs into the walls and leaves you free to naturally ventilate your building. This means that in a hempcrete home you can open the window if it gets a bit stuffy; safe in the knowledge that all your expensive conditioned heat is not going to flow straight out the door.
An air conditioner in a modern house, running 8 hours a day costs about 4 dollars or 120 dollars per month. Read more on that here: Air Conditioner costs in 2020. In subsequent years after moving into the house, the AC will work harder to compensate for increased thermal bridging, for degrading vapour barriers and increasing moisture.
What's the install process? Can I retrofit or renovate with it?
Hempcrete is a robust building material. For older houses and renovations, it is cast around existing timber studwork, therefore contributing strongly to the diagonal bracing or racking strength requirements of the frame. Hempcrete can be placed behind common exterior weatherboards, the lime binder inhibits timber rot and stabilises the timber frame, effectively preserving it.
Hempcrete also works well with standard brick veneer houses. The internal plaster and existing insulation is removed, the hempcrete is placed to fill the cavity; from the internal brickwork all the way back to the internal wall line. This creates tremendous future energy savings. Hempcrete teamed with exterior masonry works very well and is in fact the major application of hempcrete in Europe. On jobs I've worked on in the UK, Hempcrete was often adhesed internally to old stone walls for barn conversions.
Hempcrete also be retrofitted externally onto existing walls if existing eave size and design permits. In this case a lime render is applied to the external face of the Hempcrete.
All are fantastic options for creating a complete thermal envelope of the house, substantially increasing energy efficiency.
For houses with issues with damp, hempcrete can help to disperse and diffuse moisture. As opposed to dry walling where a false wall is ‘packed out’ to hide the damp issue
You could negate all your gains from a lifetime recycling and bike riding to work just by building a new house. A new build carries a carbon footprint of between 50 to 80 tonnes. Retrofitting or renovating your home not only looks great but also carries a huge carbon saving.
What can Brain Built offer?
Most carpenters solely focus on securing a job solely through the build cost. A home which performs well, post occupancy, is ultimately far more economical than ‘The Cheapest Builder In Melbourne!’. We must stop and think about the fact that a quality built house is healthier, more comfortable and more stable temperatured.
A comparison to illustrate, an architect or building designer might call for a one tonne HVAC unit per 46.45 square metres when designing a standard brick veneer home. If employing Hempcrete for the wall build-up, that HVAC requirement would drop to around one tonne per 140m2. That equates to a cost saving on heating and cooling of 68%. Calculating that saving across time and the cost differential is dramatic.
Strategic placement of thermal mass, quality natural insulation, and if possible, a design that makes use of low winter sun and protects from the high summer sun can mitigate huge amounts of energy usage.
I aim to provide renovation and retrofit options which are high performing, contain low embodied energy, don't cause respiratory and asthmatic issues though VOC ‘off gassing’, breathable, self regulating and which don't require a constantly whirring split system to moderate temperature and humidity.
I work together with clients, architects and building designers to create spectacular spaces that reflect the homeowners personality. I'm also proficient in the Sketchup design program and often come to visit clients to help tease out ideas on the laptop over a coffee to help kickstart the initial design process.
I’m also a solid timber furniture maker (link here to my work). So working with me brings the flexibility to create all solid timber furnishings (benches, feature timbers, ect.) at my Coburg workshop as part of the job. This always leads to a more cohesive design and also avoids the client having to engage other premium timber trades.
Frequently Asked Questions and further reading
Why is there an increase in rising damp, moisture and mould issues in modern housing?
The post-war usage of polythene sarking or sisilation wrap is designed to keep moisture out. Modern Australian houses are essentially sealed units. The problem is that many moisture generating activities occur inside of the house from cooking, bathing, human respiration and so on, often with the moisture becoming trapped. Humans alone can generate 115 to 270 gs of water per hour (2.8 to 6.5 kg per day) through respiration and perspiration (B.K. Kreiger and W.V. Srubar, 2019).
Combined with the common issue of rising damp (moisture creeping up the footings) condensation and mould can can and often do take root. This can be catastrophic to the building and highly detrimental to human health. We don't want our home to end up hotbox of trapped vapour; high relative humidity has solid links to asthma and a whole host of respiratory issues (see more below)
Where did this modern post-war obsession with sealing houses come from? Especially with its connection to the high amount of building failure and building insurance claims. “This has been a well-known problem for many years, in fact, previous research from over 40 years prior has reported that up to 90% of all construction material and building durability issues are caused by moisture” (B.K. Kreiger and W.V. Srubar, 2019)
When we look back to the past and see how houses were built, we begin to wonder why would we fix something that wasn’t broken?
What impact does an unstable moisture content have on human health?
“The conditions which encourage the growth of bacteria, moulds etc which affect both human and building fabric health are the same. If relative humidity is kept at between 40 and 60% then none of these viruses, moulds, fungi, bacteria can’t survive”
- Neil May “Traditional materials & Energy efficiency”
Melbourne’s average annual relative humidity is 55.8% and average monthly relative humidity ranges from 48% in January to 67% in June. So if the average relative humidity outside is safe for human health, why would we need a protective moisture barrier? Especially one that poses a threat to human health
when it fails, which it can and often does.
Conversely, hempcrete provides substantial moisture buffering, as the majority natural material do also. Hempcrete's ability to moderate and effectively blunt the evening peaks of moisture during the 24 hour cycle. It’s large mass and strong cellulose have been shown to absorb and disperse volumes of moisture indefinitely without rotting. That Hempcrete naturally keeps us in the 40% - 60% golden zone is why occupants report a feeling of general comfort. Whereas homes with moisture issues feel like muggy tombs.
Will it stand the test of time?
I was trained over in the UK by Hempcrete mastermind Graham Durrant of Hemp-Lime Spray, where we build several houses late 2019 to Christmas 2020. Graham Durrant has retrofitted period homes, carried out barn conversions and completed many new builds over the span of a decade.
Many are either repeat clients, have been passed on by word of mouth or have simply been sold on the concept after spending an evening in a Hempcrete home.
Many hempcrete homes are available on Airbnb, spending a weekend in one is a great way to really experience what I am attempting to express here. One notable house is the Sativa Sanctuary. Developed by western Australian hempcrete pioneers at Hemp Homes Australia.
What kind of air-conditioning load is required in a Hempcrete home?
In a comparative analysis of identical brick and hemp homes was carried out by the Centre for Alternative Technology in Wales, the hemp home being observed reached desired temperature of 21º C after the heating had been on for around 2 hours, and the building thermostatically maintained that temperature for the remainder of the heating period. In the brick house, however, a maximum temperature of 20º C is only reached after the heating has been on for approximately 4 hours. You could argue that the thermal mass of bricks and concrete perhaps requires too much energy to heat up to temperature, and that hempcrete is somewhere in the thermal mass sweetspot. (Centre for Alternative Technology, Wales)
At Adnams Brewery and Distribution Centre in Suffolk, building a new 4400 sq m building with 500mm thick hemp walls raised the cost of the 5.8 million pound project by 40,000 pounds, the extra outlay allowed Adnam’s to avoid installing an equally expensive 40,000 pound cooling system. Avoiding the ongoing costs and maintenance of running an industrial cooling system. The warehouse maintains a 12º – 14ºC environment. More than 500 tonnes of CO2 emissions were avoided compared with using conventional materials.
As a comparison, an architect or building designer might call for a one tonne HVAC unit per 46.45 square metres when designing a standard brick veneer home. If employing Hempcrete for the wall build-up, that HVAC requirement would drop to around one tonne per 140m2. That equates to a cost saving on heating and cooling of 68%, space that saving across time and the cost differential is dramatic.
But will it catch on fire next summer?
Hempcrete fire resistance can be observed by a test carried out for the hemp masonry company in NSW where they essentially left a lit fire at the bottom of a Hempcrete and lime plastered wall and kept of burning for over an hour https://www.hempmasonry.com.au/fire-retardant-building-materials/
Acoustics and sound dampening?
Natural insulations have higher noise dampening properties due to their higher densities and mass.
To demonstrate Hempcrete’s dampening capabitiliy, over in California some hip-hop producers employed hempcrete for a series of in studio sound baffles to great success. Here is a link to read more.
What if my house gets too hot?
When external Hemp Masonry walls are exposed to the sun they heat up very little, and when the outside temperature drops they are also able to release heat to balance the difference in temperature between the inside and outside. (Perier 2001) These properties were also confirmed by the BRE’ s tests (2001) in Haverhill.
Why hasn't it been used already?
Hempcrete is simply an elaboration of other natural methods of insulation that have existed for thousands of years. It came into use as an alternative to the clay, straw and sand mixture for use in wattle and daub, colombage or tudor style housing.
It improves upon these mixtures as hemp has unusually strong cellulose and lime remains vapour permeable whilst also, being alkaline, acts as a natural biocide, keeping the hemp shiv safe from mould and bacterial attack. Hempcrete was developed in France in the mid-1980s, when people were experimenting to find an appropriate replacement for deteriorated wattle and daub in medieval timber-frame buildings.
Why would architects design unhealthy, inefficient homes?
Perhaps the modern house is just unnecessarily complex, and therefore has unnecessary
potential for failure. We need simple, holistic houses with broad safety nets. Aeration from
the AC cannot be the only line of defense from moisture and mould. The answer lies in time
honoured and purpose evolved natural, breathable, fibrous materials to do the work for us.
The answer is not in a hi-tech house sized Tupperware container.