“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”
Melbourne’s average annual relative humidity is 55.8%. The 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? One which inadvertently locks in and builds up moisture in the home and poses a threat to human health.
Sick building syndrome describes the phenomena in which time spent in a given building has a detrimental effect on ones health or comfort. Whether it’s physical issues such as headaches, skin, eyes, nose or throat irritations and asthma; or more just a general sense of stuffiness or chill. It is a phenomena which has become more and more prevalent as modern housing moves further from what we’re evolved to live with.
A brief google will show that some of the major causes of asthma include dust mites and their faeces, moulds, spores, inorganic paint, adhesives and a wide range of organic compounds commonly found in overly moist or overly dry indoor environments.
Hempcrete and other natural building materials can address these concerns whilst also being a competitive and affordable material in the modern building industry.
Hempcrete is a low-emission material. It not only doesn’t "off-gas" or contribute to poor indoor air quality, it actually has an ability to moderate and effectively blunt the evening peaks of moisture over a 24 hour cycle. It’s large mass and strong cellulose have been shown to absorb and disperse volumes of moisture indefinitely without rotting. Furthermore, the lime binder - being highly alkaline - is a naturally occurring anti-fungal and anti-bacterial.
Hempcrete naturally keeps us in the 40% - 60% golden zone. This is why occupants report a feeling of general comfort. Whereas homes with moisture issues feel like muggy tombs.
Thermal bridging is a fancy word for gap in your insulation. Heat will always pinpoint a gap and flow through rapidly. In a standard house, that expensive conditioned air escapes through a huge array of spots. For instance, it flows through voids for power-points, gaps between stud and insulation, empty eaves, the space between windows and the stud frame, wall corners where studwork meet, missed spots due to a hungover apprentice or behind the architraves and skirting boards. Basically anywhere where insulation isn't.
Why is this important in Australia? Because of unwanted heat. It simply flows in through these gaps. It’s a phenomenon in the Australian building industry as well understood as it is under documented. And it is the major reason for the significant performance-gap between estimated energy usage and actual costs of conditioning your finished house.
Hempcrete addresses this issue so well as it creates a complete insulative envelope. You’re creating a monolithic mass of continuous insulation which wraps around and encases the entire house frame.
Hempcrete is airtight, solid and eliminates wall draughts. This is hugely important because a complete thermal envelope of the house is created. In Australia, if we can avoid heat sneaking in by stopping building draughts or ‘thermal bridging’ we eliminate the largest contributing factor to heat entry and exit.
Materials with thermal mass have the capacity to absorb, bank and release heat energy to delay temperature changes. In Italy, for example, marble banks up cool inside the home to cope with the hot Mediterranean climate. In the southern US, rammed earth shields from the scorching heat. Clay and cob homes proliferate in India and Africa. Here, in Australia, we envy those with the classic and stable mudbrick or bluestone homes which manage to keep the home cool. It's an age old technique to dampen temperature change in the home.
Flimsy modern houses lack thermal mass. They 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.
The thermal mass of Hempcrete stabilises the home. Energy sinks into the walls and leaves you free to naturally ventilate your building. A huge bonus for hemp homes is the freedom to 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.
To grasp the insulative abilities of Hempcrete best - and also to offer something more than the pop-science which proliferates the industry - I’d like to simply break down some actual research from the engineering department at Ben-Gurion University in Beersheba, Israel.
The researchers wanted to test the thermal performance of four separate one hundred square meter test dwellings with an interior ceiling height of 2.7m and three north facing windows.
What was found was that essentially even the most widely available, most highly reputed conventional leading energy efficient building material available in Australia, Hebel board, still would require almost 500 kWh more per year of energy than Hempcrete.
Moreover, when testing the ‘cheap’ option over the course of a year, the hollow-core brick used 6128 kWh more energy...
Hempcrete would require only 706 kWh per year, and only 13kWh of that being in the summer. The Air-con only switched briefly in the midst of heatwaves. The researchers also found that in winter the usage is almost half that of a Hebel-clad dwelling.
The graph represents the performance of Hempcrete during a midsummer week in scorching Israel. The energy consumption of the Hempcrete structure was the absolute lowest. Using Hempcrete instead of HCB (hollow core brick) can save almost 100% of the energy required for cooling and around 82% of the energy required for heating. Not only that, it was the building which was the most comfortable during those unbearable heat waves.
The energy consumption of the Hempcrete structure was ∼7 kWh/m2/year, which fits the highest standards of what is called ‘nZEB’ or a Nearly-Zero Energy Building.
It has also been shown that hempcrete floors (yes, you can hempcrete your sub-floor when paired with floorboards) when compared to a standard build up of R2.5 Polyester batts between floor joists would save an extra 1985 kWh per year, and chop almost an entire star off of the fabled (NatHERS) Australian star rating.
The dust from Hebel board contains crystalline silica which is harmful when inhaled. The dust is vastly more minuscule than a grain of sand and therefore is often inhaled without knowing. Exposure to silica dust can lead to the development of lung cancer, silicosis (an irreversible scarring and stiffening of the lungs), kidney disease and chronic obstructive pulmonary disease. (cancer.org.au).
Expanded Polystyrene Board (EPS board on the above graph) on the other hand is an extremely lightweight product that is composed of expanded polystyrene beads. It’s the same substance as the cups and containers that might be used to house a Halal Snack Pack or a chips and gravy. It leaches toxins over time and is a petrochemical which when “burns, a kilogram of polystyrene will release more energy than a litre of petrol” according to the Victorian Building Authority.
Today we can choose to insulate our homes with a naturally grown, carbon sequestering carbon based lifeform which not only provides the best thermal comfort but also has a genuine positive impact on the environment. So why might we squander our time by kiln firing minerals at 1500C and adding a cornucopia of chemicals and foaming agents to create something which not only performs less efficiently, leeches chemicals into the dwelling but might also even cause a devastating house fire?