Understanding The Pros + Cons Of Sustainable Building Materials

Rammed earth

Pros: Low embodied energy, high thermal mass, fire resistant and, usually, recyclable
Cons: Requires specialised contractors, provides limited insulation, is labour intensive to recycle and can be more expensive than other materials

Rammed earth walls are constructed by ramming a mixture of gravel, sand, silt and a small amount of clay into place between flat panels called formwork.

Modern rammed earth is generally stabilised using a small amount of cement (typically 5–10 per cent) to increase its strength and durability.

‘Rammed earth generally has low embodied energy and low environmental impact, but this depends on cement content and the source of the materials. Materials that are quarried and transported long distances to the construction site will have higher embodied energy and impact,’ says Nick Walters, project designer at Altereco Design.

‘Similar to concrete, rammed earth can be broken down and reused in new mixes. This involves quite a bit of effort to break the wall down and crush the material into smaller, more consistent particles in order to be reused.’

Rammed earth provides excellent thermal mass (it’s able to absorb and store a large amount of heat and then slowly release it over time) but limited insulation (which, generally speaking, acts as a shield against the entry and loss of heat).

Experienced specialised contractors are critical when building a home in rammed earth, making it less accessible than some other materials.

Hempcrete

Pros: Carbon sequestering, recyclable, high thermal mass, bushfire resistant, and doesn’t requiring painting
Cons: Labour intensive to produce, currently few Australian suppliers, and can be more expensive than other materials

Hempcrete is a composite material made of hemp, sand, and a hydraulic binder that offers a similar textural appearance to rammed earth or mudbrick.

Nick from Altereco Design says hempcrete is a ‘carbon-sequestering building material from the growth of hemp to the carbonation of lime in the walls for the life of the building… It reduces further energy consumption due to its excellent insulation and airtight qualities.’

‘Hempcrete can also help regulate indoor temperatures by absorbing excess heat during the day and releasing it at night when the temperature drops,’ says Natalie Lanksch, interior designer at Altereco Design.

In addition, hempcrete is a recyclable material that can be easily broken down to be used in a new mix. It’s also bushfire resistant (up to BAL 40), and vapour permeable (helping to regulate humidity).

Due to the labour required (and to a lesser degree, a lack of hempcrete manufacturers in Australia), this material can be more costly than other materials.

‘When you compare the overall cost of a completed hempcrete wall (with render to both sides), the cost is normally slightly higher than a typical lightweight timber framed wall with insulation, vapour membrane, and plasterboard,’ says Nick.

James Goodlet, director of Altereco Design, adds, ‘Industrial hemp is finally being grown in Australia and now there are processing facilities coming… This improves the purchase cost and upfront carbon intensity.

‘We now have a few projects that have used hempcrete as a primary material for external walls… They just feel amazing, plus you know that the home is going to provide a stable and comfortable climate year round.’

Timber

Pros: Natural insulator, low embodied energy when produced ethically, renewable, carbon sequestering, and recyclable when untreated
Cons: Low thermal mass, subject to shortages, and can be more expensive than other materials

There are hundreds of timber varieties, all of which are naturally renewable.

That being said, there are several factors to consider when using timber in construction. What makes this material ‘sustainable’ depends on how it’s harvested and transported.

‘Timber selection is quite complicated,’ says James Goodlet, director of Altereco Design. ‘This part of the industry is fraught with greenwashing. Apart from demanding suitable chain of custody certification [how the Forest Stewardship Council (FSC) verifies that forest-based materials are credibly used along the product’s path from the forest to becoming finished goods] be provided, selecting a timber species that is fit for purpose is paramount.’

Breathe regularly uses timber in their projects for structural and cosmetic purposes.  ‘Timber is a natural insulator which can reduce energy needs when used in frames, windows, doors, and floors,’ says Bettina Robinson, director of interiors at Breathe.

‘Timber can typically be sourced locally, is lightweight, and uses relatively little energy to convert the raw material to a building product, in comparison to other structural materials such as steel and concrete.’

She adds, ‘We install all recycled floorboards with nails, not glue, so they can be recycled again at the end of the building’s life.’

Significantly, timber is one of the few renewable materials that contributes to the reduction of carbon emissions. ‘Carbon from the atmosphere is taken and stored within timber during growth and makes up 40-50 per cent of its gross weight,’ says Bettina.

‘The cons of timber include that it is subject to shortages, offers low thermal mass, and it is a combustible material. ‘[Yet], timber is slow and predictable in the way that it burns, which gives it natural fire performance capabilities,’ says Bettina.

James says supplies of timber have stabilised and costs have decreased this year following huge shortages and price rises in Australia in 2021.

Clay brick

Pros: High thermal mass, durable, fire resistant, and accessible
Cons: Energy and resource-intensive to manufacture, and a relatively poor insulator

Traditional clay bricks are a durable and low-maintenance construction material. They are high in thermal mass, possess good compressive strength, and have weather-resistant, fire-resistant, and acoustic insulation properties.

For the best sustainable outcomes, Breathe prioritises the specification of bricks in the following order; locally-sourced recycled bricks, followed by Australian-made carbon neutral bricks, then Australian-made bricks.

‘Kiln firing typically requires high natural gas consumption and so is high in embodied energy,’ explains Bettina Robinson from Breathe.

‘Carbon neutral bricks utilise biomass fuel (typically sawdust) in kiln firing as a replacement to the burning of natural gas. These bricks are still made from virgin material, so the use of locally-sourced recycled brick is always preferred.’

Bettina adds the durability and lifespan of brickwork should be weighed against their embodied energy. ‘Where brickwork can serve several purposes and reduce the need for additional structure or cladding layers, we identify it as a suitable material choice.’

Mudbrick

Pros: Very low embodied energy, natural material that can be produced onsite or sourced, relatively inexpensive, recyclable, and fire resistant
Cons: Poor insulator (it’s often necessary to add insulation to mudbrick homes to achieve National Construction Code compliance across most of Australia)

Mudbrick is one of the oldest building materials in the world. This material only requires earth and the energy of the sun to produce, and therefore has very low embodied energy and environmental impact.

Mudbricks are made by mixing earth with water and fillers such as straw, placing it in a mould, and waiting for it to dry.

Despite all the material’s pros, mudbricks are rarely used in modern Australian homes. ‘It is estimated that 30 per cent of the world’s buildings are made of mud, [but] it is overlooked in the west. It is a cheap, sustainable, local and absolutely versatile building material,’ says landscape designer Sam Cox of Sam Cox Landscape.

‘[Using] human energy or labour, rather than industrial manufacturing, is key to their low embodied energy and cost. At an approximate cost of $100 a square metre — and removing the requirement of interior wall linings — it is cost effective.’

Sam used mudbrick to construct his own home in Wattle Glen, Victoria built in the year 2000. ‘We selected this material for several reasons including budget restrictions, local availability, aesthetic appeal and it also adheres to the tradition of mudbrick building in the Eltham area in which we live,’ he says.

‘I was the owner-builder, but as I was working full time, I could only work on it after hours and on weekends with the help of local trades and mates. ‘To speed things along I bought the mudbricks. They were made only a few kilometres away from locally sourced clay and delivered to the site.

‘I laid the bricks myself, rendered them with the traditional recipe of cow dung and local river silt, and painted with a mudbrick colour coat — a product developed by Grimes & Sons in Eltham.

‘It is a material that is easy to build with for an everyday person who is taking on an owner build.’

Sam attributes the declining popularity of mudbrick to modern building standards. ‘Unfortunately, mudbricks have not fared well due to not fitting the assessment process for current energy rating standards for new buildings. The mudbrick industry has since stalled in terms of new builds,’ he says.

To achieve the levels of insulation needed for sustainable house construction and to achieve National Construction Code compliance across most of Australia, it is often necessary to add insulation to mudbrick homes.

‘We are very glad to be living in a mudbrick house. It is a home that is entirely of place and embedded in the landscape… the walls have literally come out of the ground,’ Sam says.

‘I think people who are attracted to this style of home understand it as a way of life, and are not inclined to the overly comfortable, climate-controlled environment of conventional homes. Our mudbrick dwelling functions well enough for us in winter with a single wood heater and no air conditioner is needed in summer.’

Concrete

Pros: High thermal mass, accessible, usually recyclable, and durable
Cons: High embodied energy, poor insulator, and labour intensive to recycle

Concrete is the most widely used construction material in the world. Its sustainable properties are complex, as it’s a material that provides great thermal mass and is highly durable, but it is high in embodied energy.

The chemical and thermal combustion processes involved in the production of cement are a large source of carbon dioxide (CO2) emissions. Each year, more than 4 billion tonnes of cement are produced, accounting for around 8 per cent of global CO2 emissions.

‘It has high levels of embodied energy due to the mining and processing of natural resources to manufacturing, transport and product delivery,’ says Nick Walters of Altereco Design.

‘This is still low compared to MDF or glass, and very low compared to plastics, rubber, aluminium, steel and copper.

‘Concrete companies are also offering lower-carbon intensity cement mixes, which definitely make the material less carbon intensive — but still far from eradicating its intensity.’

While concrete is technically recyclable, it can be difficult to process, and currently accounts for a huge portion of construction waste.