In this series of articles, we first set out the plant-based model and how its principles can be applied to both the construction and operation of buildings. The power of such a framework is not only that it informs the choice of materials, but also that it leads to significant benefits for both the environment and people. We highlighted these benefits in the subsequent two pieces, examining how a plant-based approach can help deliver net zero carbon buildings that are simultaneously healthy for people.
Here we return to the issue of materials. We evaluate current and forthcoming plant-based products that are likely to alter what and how we build. We also look at plant-based options and the opportunities and benefits they present. We then explore the likely winners as plant-based materials further enter the market.
We believe successful plant-based materials will mimic the qualities of conventional products (in terms of strength, functionality, etc.) while providing sustainable benefits. Over time, as sustainability concerns mount, they will become increasingly attractive, not as alternatives but as products of choice.
Three key messages
Although it can be difficult to predict which materials will succeed, especially in such a rapidly evolving market, three messages are clear:
- More plant-based materials are beginning to find their way into construction projects. The reasons for this are many. Plant-based materials tend to have lower embodied carbon at a time when net zero carbon is the dominant ESG issue - they promote health and wellbeing, which is an important occupier expectation and they satisfy a variety of other sustainability criteria (circular economy and waste considerations, local products, etc).
- The materials themselves are becoming more diverse, advanced and commercially viable. Plant-based mainstays like timber and bamboo continue to grow in popularity, but other more exotic materials like fungi and algae are becoming attractive options, albeit in earlier stages of development.
- Some barriers to wider adoption remain. Entrenched ideas and practices, not to mention regulation, can dampen the uptake of alternative materials. But there are signs that this is changing, as evidenced by the growth of timber building in the UK and recent regulation in France that mandates bio-based materials in new construction. Such actions are the first indicators of much wider changes in industry and government.
Why plant-based materials, and why now?
The perceived viability of plant-based materials has changed over the last few years. One important reason for this is how easily such materials can address climate change.
Unlike carbon-capture technologies and innovative new materials that need significant money and time to develop, plant-based materials represent an existing, practical and low-cost solution.
Historically, concrete and steel have been used almost exclusively to build the world’s tall, modern structures. Plant-based materials are typically confined to lighter and lower buildings. This is changing. Plant-based materials are beginning to form the backbone of buildings, including high-rise structures. Advances in materials, new drivers (such as embodied carbon) and changing practices and attitudes are all encouraging a more bio-based approach.
For many, timber is the first and most natural choice for a plant-based alternative to more carbon-intensive construction products like steel and concrete. The use of timber is an essential element of any net zero carbon strategy, including its incorporation as part of the building structure.
The growth of mass timber in the last few years as a low carbon solution is undeniable. Historically, buildings built with timber were confined to less than 10 storeys, but the height of timber-based structures has increased substantially. Engineered timbers have added strength, allowing them to be used in place of more energy-intensive materials like steel. These products can often be cut to measure offsite before being transported and erected at greater speed. The potential benefits are three-fold: less embodied carbon, faster programme and lower construction costs.
Some engineered woods, such as cross-laminated timber (CLT), can be stronger than steel, with the same carbon-saving advantages as standard timber. This has created opportunities to build structures approaching 100 metres in height. For a good overview of mass-timber opportunities and its potential, see the G&T Modern Methods of Construction section on our website.
Despite the growing popularity of timber, it still faces some challenges, particularly in finding acceptance from insurers. However, this appears to be changing. There is little question that in the UK and globally, the use of timber – in structure, internally and even as a façade material – will continue to increase. This will be both a response to net zero considerations but also for aesthetic factors, as the use of timber “signals” sustainability in a way few material choices do.
Bamboo is a fast-growing and renewable plant that has proven to be a viable alternative to other conventional materials in construction. It is available in most locations globally and grows much faster and sequesters more carbon than timber. This makes it a top choice among plant-based materials.
A growing body of research shows that certain bamboo species have impressive and efficient mechanical properties, including possessing a strength-to-weight ratio equal to or better than that of steel and lumber. Certain bamboos also have the compressive strength of concrete. In recent years, the bamboo skyscraper idea has achieved recognition, although demonstration of the concept remains to be proven.
At the same time, the strength of bamboo could make it a sustainable substitute for traditional rebars. Although not as accepted as mass timber or regular timber in Europe, there are indications that bamboo structures may be as strong, or stronger than, engineered timber with lighter weight. Therefore, the possibility of its use in much taller structures remains a tantalising idea.
Interiors and finishes
There are many interior applications for wood and bamboo - these are well known and widely used. But there are many other bio-based materials available and new applications for these materials are emerging all the time. While it is true that that the structure and superstructure require the most embodied carbon (in a whole life carbon analysis), there are still many ways that clients can use plant-based materials to lower construction carbon and improve the quality of the indoor environment.
Hemp provides a woody stalk used in innovative building materials, most notably hempcrete. Hempcrete mixes natural fibres with lime to produce a concrete-like substance and finish (although without the load-bearing capabilities of concreate). Bricks can be made with hemp, water and lime-based binder and are suitable for walls, floor slabs or insulation. Hemp flooring tiles can be made by combining hemp stalks with soy-based adhesive. Hemp is also used as a natural insulation.
Hemp is naturally fire, mould and pest resistant and has excellent acoustic thermal insulation properties. It is lightweight, strong, and breathable and comes from a rapidly renewable resource.
Construction panels made from straw represent an elegant, practical, inexpensive and low carbon option. Straw, which is an agricultural by-product of wheat and other cereals, is 45-50% atmospheric carbon by mass, meaning that buildings that use this material can effectively become a carbon “sink.” Straw is created from renewable energy (the sun) and effectively stores carbon over its lifetime in the building.
Bio-based modular systems have begun to be championed by green buildings councils, including the UKGBC, although to date applications have been on smaller scale residential projects. However, there is no reason why the same technology and materials could not be used on larger buildings. Indeed, this is beginning to become more commonplace.
Straw panels tend to be tightly packed and rendered on the exterior, which reduces their flammability. Nevertheless, there are concerns about the associated risk of fire to overcome and regulatory limitations on where straw can be used.
Other examples: existing products
The range of other plant-based materials currently available is extensive. There are plant-based paints and finishes, plant-based floor and wall coverings, insulation and so on. In the last couple of years, companies have begun to understand and market products using the “plant-based” moniker, no doubt due to its popularity in other industries.
Other plant-based alternatives are more at the prototype stage, although they are no less exciting. Two particularly important examples are algae and mycelium. Their capacity to work with other plant-based products, particularly waste streams, is especially important, as it extenuates the credentials across the entire product – produced by renewable energy, acting as a sequester, non-toxic, biodegradable, etc.
Algae produces a cement-like substance that is capable of bonding together sand with gravel or stone to make concrete. This “biogenic limestone” is what produces strong structures like coral reefs. By using biogenic limestone instead of quarried limestone as the filler, cement could become not only net neutral, but also carbon negative by pulling carbon dioxide out of the atmosphere and storing it permanently in the structure.
Companies have already used this process to produce bricks of comparable strength and durability to conventional bricks but which only use 1/10 of the carbon to manufacture. Algae can also be used to make a variety of other construction products, including tiles and façades.
Algae’s appeal goes beyond its carbon properties. Algae has also been used as part of buildings to actively purify the air. When incorporated into structures and activated by sunlight, the algae generates oxygen and “eats” carbon dioxide – a perfect example of a plant-based material also demonstrating plant-based principles.
Mycelium, which is essentially the root of a mushroom, is another versatile material with wide range of potential use cases. Mycelium is a fast-growing binding element that can fuse with other materials to produce industrial-strength products, including bricks and other structural materials.
Products with mycelium are “'grown” rather than chemically 'manufactured', making it a future option with low-embodied carbon characteristics. Mycelium is compostable and biodegradable, durable and resistant to water, mould, and fire. What sets mycelium apart from other materials is its ability to regenerate at a quick rate.
Mycelium is typically combined with local agricultural waste and water in pre-made growing moulds, where the mycelium takes shape over several days before being heated and dried to create a stable material that can be used to make a variety of products. As with algae, mycelium is particularly useful for its binding properties that occur naturally and do not require as much energy to produce.
Challenges to great uptake
Whether it is questions about flammability and durability, or simply familiarity with conventional products, the adoption of plant-based materials will take time. It is understandable, given concerns about health and safety – not to mention regulatory compliance – that the route to market would be a slow one. The consequences of not being 100% correct about construction products and practices are too severe not to be cautious. Hence, some of the limitations placed on these products by building regulations.
In the next article in this series, we will look at regulatory and industry barriers, including funding, insurance and underwriting. There has been, and continues to be, a reluctance to fund and insure plant-based buildings and the generally risk-averse construction industry has yet to embrace plant-based materials on a large scale. There are many more hurdles to mortgaging and financing bio-based projects than those constructed with conventional building materials.
Having said that, the ramifications of climate change and its simultaneous impact on health and wellbeing are also critical. That is why more products are coming to market and many of them are matching – or exceeding – the performance of conventional products, with the added benefit of being good for the environment.
More acceptance of these materials is being reflected in regulation, where lawmakers are beginning to express a preference for bio-based products and practices. France, for example, has recently passed regulation requiring new buildings to contain 50% bio-based products. This is likely the direction of change for more countries, especially as plant-based products demonstrate that they can meet the certifications required for construction products.
New products take time not only to develop, but also to gain industry and (later) mainstream acceptance. If the last few years are any indication, we can expect a variety of products to emerge, albeit with less mature routes to market. The supply chain for plant-based products is not as well-developed or extensive as for conventional products, and there are lingering questions about supply, quality, liabilities, insurance, compliance and the like. Most suppliers of bio-based materials are smaller than conventional competitors and do not have the economies of scale, marketing budgets or large-scale manufacturing capabilities. All of these will slow the adoption of plant-based materials in predictable ways, at least in the short term.
Nevertheless, there are countless opportunities for plant-based products. It is not a question of if these products enter the market, but when and to what extent. Given the diversity of products, their ability to match the performance of conventional items and the demand for low carbon and healthy alternatives, the answer appears clear.
Plant-based options in other industries have outpaced conventional products as concerns about environmental and personal health have dominated consumer preferences. Given the availability of plant-based construction products, it is not hard to see why the same demands are beginning to similarly transform construction and real estate.
How we can help
Through its creation of – and ongoing work with - the Mass Timber Forum, G&T continues to provide expert advice and practical guidance on emerging bio-based materials. Many of our projects are incorporating a bio-based approach to net zero carbon and healthy buildings, including innovative projects like 2 Copper Square and Hardman Square Pavilion. We therefore understand the cost, programme and other implications of introducing plant-based materials into buildings.
If you have any questions, or would like further guidance, please get in touch with the team.