Fire safety and design  

Naturally fire-proof materials: hemp, seaweed and charred timber

Addressing the importance of fireproofing a building, architects are increasingly incorporating sustainable materials into their projects (such as wood and stone wool), which are not only fire-proof, antibacterial and breathable but also are easily recyclable.

Here we look at three naturally fire-proof materials that have a long-standing architectural history: charred timber, hemp and seaweed.

Charred Timber

An effective method of making wood fire-proof is to use fire. Charring is the process of applying heat to a wooden exterior for a short period of time which alters the thermodynamic conductivity of the material and its cellular structure. Burning the cellulose later leaves a blackened lignin behind (via pyrolysis) which when faced with fire again, can handle much higher temperatures and longer contact with the flame source. The char decreases the rate of burning as it acts as an insulative material, protecting the wood underneath and increasing the depth of the charring makes the material increasingly fire resistant.

A charred timber building called ‘7th Room’ is the latest addition to Treehotel- a 10-metre tall construction which stands above the Swedish forest floor. Designed by Scandinavian architectural practice Snøhetta, the outside is covered in charred timber and the inside is aligned with light-coloured wood. The building is supported by 12 columns, weighs 40 tonnes, and has a stargazing net to allow a view out to the Swedish Lapland, the Lule River and the aurora borealis. The charred timber not only blends into the Swedish forest but acts as an effective fire-proof material.

7th Room. Image credit: Johan Jansson 

7th Room. Image credit: Johan Jansson 


Hempcrete, also known as hemplime, is a bio-composite material that has been used in Europe for decades, and as part of an emerging trend in the west, many architects are incorporating hempcrete into sustainable architectural designs.

Hemp provides insulation, contributes to a warm indoor environment, and is fire-proof. The tightly packed cellular structure and the thickness and of the walls contribute to the material’s fire resistance whilst its porous structure allows a fire retardant chemical to seep into it. Also a vapour-permeable hygroscopic material, hemp absorbs moisture from the air when humidity is high (releasing it again when the outside levels decrease).

Hempcrete is constructed by mixing industrial hemp with sand, water and lime which creates a low-density carbon negative material. Hemp's porous structure also gives it excellent conductivity and hygrothermal qualities and it is also impervious to mould and pests (e.g. mice and cockroaches). 

An example of the use of hemp is Ein Hod, an eco home for artists, designed by Halfia-based studio Tav Group. Situated on a hillside in a rural Israeli village, Elin Hod is a fire-proof construction with solar panels, minimising the amount of energy needed to run the building. Ein Hod is constructed with hempcrete, timber and rammed earth, making it a naturally non-toxic space. Tav Group architects chose hempcrete for its fire-resistance and carbon sequestration benefits and having lime coated the material, the building has antifungal qualities.

Ein Hod. Image credit: Yaeli Gavrieli and Tav Group.

Ein Hod . Image credit: Yaeli Gavrieli and Tav Group.


Seaweed is a fibrous, malleable and tightly cellularly packaged material, historically used for wall insulation by the Ancient Greeks. With its tightly packed cellular structure, seaweed is not only insulative but also fireproof. 

Built on the small island of Læsø in Denmark in 2013, The Modern Seaweed House is an example of seaweed performing as an efficient construction material. Developed by Realdania Byg and designed by Vandkunsten Architects, the building is constructed with timber and insulated with seaweed.

Seaweed houses are an established part of Danish architecture, and the traditionally used for roof and ceiling insulation. However, The Modern Seaweed House uses seaweed slightly differently, stuffing the material into nets which are attached to the roof and facade, allowing the building to keep a constant temperature throughout the winter, absorbing water particles, and acting as a fire deterrent due to its packed compression.

The Modern Seaweed House.  Image credit: Helene Høyer Mikkelsen.

The Modern Seaweed House.  Image credit: Helene Høyer Mikkelsen