What biomaterials mean for construction

Biomaterials are set to dominate 21st-century construction and energy production. Currently we have little or no experience of these, but three innovations – hempcrete, green walls and algae building technology – will be increasingly adopted in the built environment.

Because conventional concrete has a high level of embodied energy, the construction industry should be considering these alternative materials, where biological principles and engineering are used to create viable building products.

Similarly, green infrastructure such as green roofs, facades or walls, can help mitigate urban temperature increases caused by climate change. These building features can also improve air quality, provide habitat for biodiversity and improve the thermal performance of the envelope.

Questions remain over how far these outcomes are or will be achieved, and whether these technologies can be used together; but research now under way should offer insight into the potential for combining them.

One such biomaterial is hemp lime, also known as hempcrete. It is most commonly used to construct walls, but can also be used for a light, highly energy-efficient form of cladding. This means there are hempcrete products for roofing and subfloor insulation, and others that can be sprayed or formed into blocks or panels.

These systems tend not to be load-bearing, but are effective as insulation or soundproofing. Their breathability also reduces the occurrence of mould in buildings, and has a correspondingly positive effect on indoor air quality.

Compared to conventional construction materials, hempcrete also has a lower density, meaning that it reduces the dead loads on buildings. The building system results in zero waste going to landfill as well.

Furthermore, it can help prevent the spread of fires. Research conducted by the Australian Hemp Masonry Company, for instance, demonstrates that the substance complies with the fire standards of the Building Code of Australia. Tests have confirmed that, subject to an hour of flame or a gas burner, hempcrete walling materials neither ignite nor smoke.

The 2015 UK report Renewable Hempcrete House: Energy Efficiency Monitoring Programme, funded by the Low Carbon Investment Fund, established how far energy consumption and carbon emissions could be reduced by using the proprietary product Hemcrete.

The report demonstrated that its insulating properties, as shown in Table 1, allow for smaller heating equipment to be used, meaning that energy consumption and carbon emissions are correspondingly reduced. This difference could be in the range of 50–80% lower than buildings with conventional brick-and-block construction insulated to the same U value.

The Hemcrete structure also represents potential for carbon sequestration, as the hemp from which it is sourced draws carbon dioxide from the air in the course of growth, as does carbonation of the building material during its service life. This results in a negative embodied carbon footprint of –4.3 tonnes for a two-bedroom, two-storey UK terraced house, compared with a footprint of +10.7 tonnes for a brick-and-block property of the same dimensions.

Where external walls are very thick, they are able to meet the voluntary energy efficiency standards set by Passivhaus. In addition to this effective thermal performance, hempcrete creates a breathable building envelope that helps improve indoor air quality, manage internal humidity and moisture and increase comfort. 

Hempcrete also allows for varying internal finishes, to create different aesthetics suitable for new commercial and residential buildings as well as for retrofitting existing properties to improve energy efficiency. This offers significant opportunities for reducing the carbon footprint of construction.

Further research on the hygrothermal performance of hempcrete buildings, funded by an Australian Research Council Linkage grant, is now being conducted by a partnership between University Technology Sydney (UTS) and Australian Hemp Masonry Company.

Green walls – sometimes also called living walls, green facades, bio-walls or vertical vegetation – refer to plants grown directly on a building's facade or on a separate structural system, which can be free-standing or attached to the facade. Alternatively, vegetation may be grown in planter boxes and trained on a trellis with mechanised watering.

There are generally two types of green wall: soil-less and modular. The former are effectively vertical gardens grown on building surfaces, mimicking conditions found where climbing plants grow up rockfaces naturally.

Modular green walls on the other hand comprise plants, including climbing plants, and soil or growing media in prefabricated modules. The cost is generally about half that of a soil-less wall on a per-square-metre basis.

In 2016, RICS published the Green roofs and walls guidance note, Australia, which outlines considerations for designing and installing such features. It also covers assessing a building for retrofit, and managing water consumption, pests and maintenance inspections.

There is as yet no evidence for the combined performance of green walls and hempcrete. However, it is likely that the environmental benefits of each system would mean they work well together to reduce building energy use.

Significant barriers to adopting green walls remain, given the costs. Maintenance also presents health and safety risks, with workers needing to operate at height using scissor lifts or gondolas, or having to abseil.

To address this, UTS researchers have designed and prototyped a so-called Wallbot, for monitoring and maintaining green walls. Field tests of the Wallbot will be undertaken on prototype hempcrete and green wall structures at UTS.

Current trials of the technology at UTS will demonstrate whether the biomass produced could fulfil energy requirements for Australian housing designed to Passivhaus standards.

Meanwhile, a feasibility study at UTS is investigating the potential for ABT on a range of building types and in various locations. Other possible uses of algae include on-site remediation of grey water, which can then be used to water green walls.

UTS is also commissioning algae prototype panels to assess biomass production potential in Sydney and test control systems for cleaning and maintenance, as a pilot for a larger-scale project. This will improve understanding of ABT performance, including energy production, durability and maintenance requirements.

The research will also enable the development of guidance notes for surveyors involved in the design, specification, costing, repair and maintenance of ABT during its life cycle, as well as decommissioning in line with the principles of the circular economy.

But this knowledge is being extended all the time, and will result in guidance that enables practitioners to specify and work with confidence on buildings using these technologies.

Sara Wilkinson FRICS is professor of sustainable property at the University of Technology, Sydney
Contact Sara: Email

Peter Ralph is professor of marine biology at the University of Technology, Sydney
Contact Peter: Email

Arnaud Castel is professor of civil and environmental engineering at the University of Technology, Sydney
Contact Arnaud: Email

Klara Marosszeky is managing director of Australian Hemp Masonry Company
Contact Klara: Email

Related competencies include: Sustainability

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