Hempcrete strength is its simplicity, or because of what it is not.
A standard Australian wall can comprise of brick veneer, insulation, sisalation, 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.
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.
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.
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.
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/
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.
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.
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.
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.
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?