DeepDive: The return of “old” construction materials – bio-based and local

At White Arkitekter, we have set the ambitious goal that by 2030 all our projects will be climate neutral. To achieve this, we need to constantly develop our way of working and find new solutions that can contribute to the goal.

– We have limited resources that we can use in projects to stay within our climate budget. On those occasions when we cannot use reused materials, it is important that we choose new materials that are bio-based and have a low carbon footprint or even a negative footprint. This means materials that store more carbon dioxide than they release, such as lime hemp, where carbon dioxide has been stored as the hemp grows and the lime binds carbon dioxide as it carbonises, says Anna Lisa McSweeney.

One of the world’s oldest building materials, unfired clay can be produced, used, and transformed with low energy and resource consumption. Because unfired clay is bound together by ionic rather than chemical bonds and does not need to be heated during production, no carbon dioxide is emitted during the process. Moreover, because clay is malleable and comes in many colours, it allows for a rich palette of aesthetic expressions. Johan Jönsson is a sustainability specialist and, together with colleague Marja Lundgren, is the initiator of the standard development of unfired clay that we run together with the Swedish Institute for Standards (SIS).

Local materials are essential
Johan Jönsson points out that while clay has a low carbon footprint, transport is a relatively large part of this, so for the whole chain to be sustainable it is crucial to use materials that are available locally. In Dumfries, Scotland, in collaboration with O’DonnellBrown Architects and Ekkist, we are designing The Crichton Project, a cultural centre that uses natural and local materials with low carbon emissions and health benefits. The project is our first in the UK using rammed earth, which is also The Crichton Project’s primary material.

Thick rammed earth walls, made using local soils pigmented with local sandstone and crushed red bricks of the existing building, ties in with the colour tone and hues of the adjacent sandstone buildings. Thanks to the thermal mass of the soil, the material regulates the temperature while its hygroscopic properties absorb moisture, helping to regulate humidity which in turn improves air quality. Rammed earth buildings also allow for good airtightness levels, helping to reduce heat loss in winter and heat gain in summer.

Health benefits
Studies show that people tend to respond more positively to natural materials, many of which have health benefits. As well as being an antiseptic, unfired clay is also reactive to moisture, helping to keep the humidity ratio of a room at an even level. This is good for the skin and mucous membranes, among other things. An even humidity ratio also minimises the risk of mould growth while the material acts as a filter against particles and viruses, which leads to less spread of infection and potentially less need for ventilation.

In Wales, we are currently working on the new Velindre Cancer Centre. The building has been designed to maximise the use of local and natural materials that reduce embodied carbon. Wood and other natural materials such as lime and clay plasters are breathable and flexible, creating a natural and calming environment for patients, their families, visitors, and staff.

Specified timber has been used for the lounge, radiotherapy and waiting areas and some walls use clay plaster. Hemp blocks will also be an important component in the new Velindre Cancer Centre, contributing to a calming environment. Like clay, hemp and lime keep the humidity at an ideal level for the lungs, while lime is also alkaline and thus has natural antibacterial properties.

Challenges and the way forward
Although there are many advantages to unfired clay, there are also some challenges and factors to consider when using it as a building material, Johan Jönsson points out.

Both Anna Lisa and Johan hope and work for the materials to become more common on a larger scale in the future, but for this to become a reality, both believe that knowledge and standards are required.

– Introducing standards creates a basis for guarantees and insurance, which in turn increases the demand and willingness to use the material. The client needs to know that the materials used in the project are compliant with building regulations and the contractors need to be able to manage it. This is something that tests, training and standards can help with, says Johan Jönsson.

CONTACT

Anna Lisa McSweeney

Architect

London

+44 750 751 55 06

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Johan Jönsson

Stockholm

+46 8 402 25 64

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