Why the development trade wants hemp and fungi

Bio-based construction materials are already on the market. What will it take to scale them? 

From 2020, the world can emit only 350 gigatonnes of carbon for a chance to stay within 1.5 degrees of warming. Maintaining the carbon budget will require a radical overhaul of how we make our buildings. Currently, manufacturing construction materials emits around 11 percent of global greenhouse gases per year globally. Around 5 percent of global GHG emissions come from cement alone and we are set to produce 3.5 billion metric tons of it by 2050.

The carbon intensity of the construction sector owes to its near-total reliance on metal and mineral-based materials. By adopting bio-alternatives to cement, steel, brick, and concrete, the industry could make massive sustainability savings. Because plants absorb atmospheric carbon as they grow, components made from biomass are much more likely to be carbon-neutral.

Although wood has been the traditional plant-based construction material, it cannot meet address the sustainability needs of the industry alone. Timber forests fluctuate in their carbon storage capacity since felled trees take a long time to regrow. This lag between timber harvest and regrowth also makes it difficult to supply the amounts of biomass needed by the global industry without destroying natural ecosystems for new plantations.

Timber is no longer the only option when it comes to organic building materials, however. Insulation and structural components made from straw, hemp, and mycelium are now hitting the market.  Unlike wood, these crops regenerate quickly, offering plentiful bio-feedstocks and sustained levels of carbon storage. A 2019 study showed that hemp and straw can help achieve carbon-negative buildings – something near impossible with clay bricks or concrete.

Hemp insulation and building blocks

Switching to bio-based insulation is an easy route to low-carbon buildings. Over its entire life cycle, one kilo of bio-based insulation requires between 0.24 and 39.5 megajoules to manufacture. Compare this to 15.7 – 54 megajoules per kilo for mineral insulation and between 95 and 108 for oil-derived versions.

Hemp wool is a leading bio-based insulation alternative. This material is made by blending hemp fibres with polyester, potato starch, or sodium carbonate to produce a lightweight fleece-like material that matches fibreglass or foam equivalents on performance. Because it contains few synthetic ingredients, it poses lower health risks than mineral or metal-based versions which have been associated with skin and lung abnormalities. Hempitecture, a US company that makes hempwool that is 90 percent natural fibre, claims their products are “safe to touch and handle without gloves”.

Hemp can also be used in walls, roofs, and floors in the form of ‘hempcrete’. Like concrete, hempcrete can be bought in prefab blocks or be moulded on-site. This biocomposite is created by blending hemp shiv (the woody core of the hemp plant) with lime binder (hydrated lime and either natural hydraulic lime and Portland cement) or a pozzolanic binder like metakaolin. On average, hempcrete weighs an eighth of concrete, saving on transportation emissions.

A 2021 study that tested a hempcrete wall for eight months at high humidity found that Hempcrete is insulating and mould-resistant, highly suited to the wet climate of Northern Europe. France recently created a 380 square metre sports centre near Paris made from the material, the country’s first public hempcrete building.

Many natural building companies now offer hempcrete, including Hempitecture, US-based Americhanvre and the UK company Hempcrete. The Belgian company IsoHemp produces more than one million hempcrete blocks per year and claims that one pallet of their hempcrete blocks stores 100 kg of carbon dioxide.

Hempcrete offers benefits beyond its carbon mitigation properties. Unlike conventional structural materials like brick or cement, it offers excellent natural insulation. This cuts back the need for additional heat-retaining fillers. The material also naturally regulates indoor air quality. Its pores collect water molecules until the water content of the material balances that of the air surrounding it.

Hemp-based building materials have been a major focus for EU R&D in sustainable construction. In 2018, the EU-funded ISOBIO project came up with a new formulation for hempcrete, replacing the mineral lime binder with bio-based alternatives. ISOBIO’s 100 percent bio-based hempcrete has better thermal conductivity and strength than hemp line blends.

Circular buildings from fungus

GHG emissions are not the only problem with today’s building materials. Recyclability is also an issue. At the end of its life, concrete is crushed and sent to landfills. This linear model intensifies virgin resource extraction and carbon-intensive manufacturing to replace the lost material.

Mycelium building blocks provide an answer. Mycelium is the long, threadlike vegetative and root structure of a fungus. When a substrate like shredded bamboo or straw is inoculated with its spawn, the growing mycelium winds its way around the pieces to create a dense network of threads. To deactivate mycelium growth, the substance is heated to high temperatures. The texture and colour of the final product resemble a block of hard cheese. Different cultivation methods produce blocks that vary in durability, stiffness, and density.

The world’s first large-scale fungi building was the Mushroom Tower pavilion at the Museum of Modern Art in New York installed in 2014. This 13 metre structure, made using mushroom and corn stalk waste, was built to showcase the possibilities of the material. Within six weeks the bricks were returned to high quality soil for the local gardens.

Lightweight, naturally fire resistant and free of the toxic volatile compounds that emanate from some treated timber, this fungal block is an exciting new candidate for organic construction. In addition, the carbon savings are immense. Producing a 1 m3 block of mycelium- based material releases 31 kg of CO compared to 410 kg for the same amount of concrete containing 14 percent cement.

Under stable climatic conditions, these blocks can retain their integrity for 20 years. However, under normal conditions, the material naturally decomposes in 60 days. This is because the water resistance of mycelium decreases rapidly. This characteristic makes mycelium suited to temporary structures rather than heavy construction. Mycelium could find its niche in the events sector, allowing accommodation and venue space to be built and dismantled in a short period.

Most mycelium production occurs at a small scale. The largest scale producer today is the New York-baesd startup Ecovative, the first commercial producer of mycelium construction materials. Their fully-automated labs create 215 m3 of mycelium-based materials per hour. Vital research into how cultivation methods can influence the properties of mycelium is being conducted at the Centre of Expertise Biobased Economy. There, they are focusing on ways to improve the strength, insulating capacity, and, crucially, the moisture resistance of fungi building blocks.

What will it take to scale bio-based building materials? 

1.51 million metres squared worth of new buildings are expected in Europe alone by 2050. Yet the challenge of scaling sustainable bio-alternatives to meet this demand is immense.

The higher cost of bio-based building materials is the major factor limiting their uptake. To solve this, companies need to create products from feedstock that is widely available locally. The Dutch bio-construction company Holland Houtland has identified enough material from horticultural waste streams to scale without destroying natural habitats.

Selecting land-efficient biomass is essential so that cultivating feedstock for the construction industry does not compete with agriculture. This means that the biomaterials that will scale in one region or country may not in another.  For example, hemp shiv is a byproduct created when hemp oil is extracted. Legal limits on hemp cultivation mean that currently, Europe has only 1 percent of the total land that would be needed to comfortably supply the construction sector. France may be an exception to this, coming third in terms of worldwide hemp cultivation. In other major hemp-producing nations like Canada, China, and the USA, there is huge potential for a non-land intensive bio-materials sector.

Emphasising the full benefits of bio is also key. In 2021, a research paper on scaling bio-based circular construction in the UK found that industry respondents who had switched to bio-based materials dramatically reduced their building maintenance costs. One reported that a hempcrete building costs two-thirds less to run than a traditional building. Another reported that a warehouse built with sustainable materials saved six figures in energy costs. Shifting the way businesses think about financial risk is an important determinant of whether bio-based materials can become a widescale solution to the energy transition.

Customers who adopt bio-based materials are quickly dispelled of the notion that they cannot perform as well as conventional materials. However, overcoming mainstream perceptions about physical performance remains a major obstacle to increasing demand. There needs to be a greater push on educating the industry about advances in bio-materials engineering and making them aware of the options available on the market.

The bio-based construction industry must also underline its importance in national net zero policies at every turn. “If politicians want to build one million new houses in the next ten years AND stay within the 1.5 degrees of the Paris Agreement, they have to do it right the first time and use the right materials.” Says Sandra Nap of Holland Houtland, a bio-based construction materials company.

Obtaining government contracts to build green social housing is a crucial way to boost demand and will kickstart scaling. Holland Houtland has recently received funding from the Bult by Nature Accelerator Fund to develop bio-based social housing and conduct value assessments on buildings with bio. The first successful green social housing project would go a long way to proving that bio-based buildings can simultaneously meet economic and sustainability challenges.