As one of the most sustainable building materials available today, it’s no wonder rammed earth is making a comeback.
Oliver Petrovic, managing director of Olnee Constructions that specialises in rammed earth construction, says rammed earth construction in Australia usually refers to stabilised rammed earth (SRE). SRE is essentially a blend of raw materials, mixed with a small percentage of cement, water and waterproofing. The material offers low embodied energy, high thermal mass, strength and durability, zero maintenance, sound insulative qualities, fire resistance, and of course, inherent beauty.
‘If designed well, a home incorporating rammed earth can feel warm inside during cold weather, and cool inside during hot weather, without relying on active heating or cooling systems,’ says architectural designer Zana Wright, whose own home features rammed earth. ‘Another important pro is that earth doesn’t burn, which makes rammed earth a great choice for bushfire-prone areas. After such a horrific bushfire season, it is becoming increasingly obvious that we need to build for a changing climate.’
Due to the fairly specialised and labour intensive process, Zana says rammed earth can be more costly than other wall systems, at approximately $300-$400 per square metre of wall face. ‘However, as it incorporates all the elements of a wall in one, its total cost is not a great deal more than a more complex conventional wall which involves building a structural frame, installing insulation, sarking, exterior cladding boards, interior lining boards, and painting both inside and out,’ Zana says.
Experts hope that with more education, rammed earth will become a more widely used material in Australia. ‘If there were any cons, it would be that it can’t always be built on very small properties or properties with poor access, due to the nature of the construction system,’ says Oliver.
Bricks offer a timeless look, and when used appropriately, they are one of the most sustainable building materials. As well as providing great thermal mass properties (the ability of a material to absorb and store heat energy), Angus Crisp, principal of sustainable builder Crisp Green Homes, says bricks can be reused multiple times, or alternatively made into road base or crusher dust.
While they stack up on energy efficiency, bricks can be a relatively high cost material, partly because of the need for a specialist trade to install them. As with rammed earth, though, using bricks as a key construction material can also reduce the need for exterior cladding, interior lining boards, and painting (we do love an exposed red brick wall!) – so when comparing costs, it’s worth taking this into account.
Ethically sourced timbers are another sustainable option to use in residential construction. ‘It’s a renewable resource and, if sourced and milled responsibly, is probably the most sustainable building material available,’ says architect Ben Callery, director of Ben Callery Architects.
Various bodies exist to certify where and how timber has been sourced, including the Forestry Stewardship Council (FSC). ‘This is a worldwide not-for-profit group that investigates and audits supply chains for timber, and uses sustainability as one of its 10 key parameters,’ says Angus Crisp. ‘We also as a company prefer to use Australian timbers rather than imported, as to also reduce any carbon miles from shipping.’
Likewise with brick, using recycled timbers from the outset is the best way for consumers to minimise their environmental impact when building.
A downfall of timber is its lack of thermal mass, but Ben Callery assures this material can still be an effective insulator. ‘Thermal mass isn’t an essential in sustainable design. Some of the most thermally efficient buildings in cold climates in Europe don’t use thermal mass at all – the focus is more on higher levels of insulation,’ he says.
The sustainable qualities of concrete are complicated. On the one hand, concrete is a versatile material that offers good thermal mass, but on the other, it’s very energy intensive to produce. ‘Unfortunately, the main material used in concrete, cement, has a very high carbon cost. The steel reinforcement required in concrete also has high carbon costs,’ says Angus Crisp.
To reduce the environmental impact of concrete, look for varieties with some recycled content. ‘We’re very mindful of the embodied energy of concrete, and try to use concrete with recycled content where possible,’ says Ben Callery. ‘But, if the building is going to be there for a long time and the thermal mass will contribute to the performance energy efficiency of the building, then that can start to offset that embodied energy,’
In partnership with Bank Australia, we’re bringing you ‘Building Better’ – a series aimed at demystifying sustainable renovation ideas and building upgrades. Revisit our previous stories on solar power and interior design.
If you like building better and are interested in green homes, Bank Australia’s Clean Energy Home Loan offers a discounted home loan rate if you buy or build a home that exceeds a 7-star NatHERS rating, or have made ambitious green upgrades in the last 12 months. Find out more.