Timber is one of the oldest building materials and it is key to the future of sustainable construction. However, this natural material is flammable. We are often asked if yakisugi charring, the Japanese preservation technique we use to create Shou Sugi Ban® cladding results in fire-rated timbers. We explain the answer in this article.
Historic & Contemporary Wooden Buildings
Around the world, there are examples of centuries-old, historic wooden buildings and many award-winning contemporary architecture featuring timber cladding and structures. Architects and carpenters have learnt the right types of timber and techniques to use to create simple to spectacular wooden constructions.
However, timber is hygroscopic, which means it expands and contracts in response to moisture content. It is also an ideal home for insects and can be susceptible to mould and fungi growth. Therefore, timbers need to be treated to protect the strength, durability and lifespan of this building material.
There are many chemical applications including oils, paints and varnishes which offer a protective surface finish. Yet, in Japan, the controlled charring of timber has been widely used as a preservation technique. One advantage is that the treatment is long lasting and doesn’t require annual re-application of finishes to maintain protection.
Impact of Carbonisation on Timber
The process of charring wood in a controlled manner, at the right temperature and to a specific depth alters the cell structure. It releases natural resins, which help to protect and preserve the timbers. The yakisugi charring process increases biological resistance which includes:
- Minimising the effect of UV light, which causes weathering and fading in untreated timbers
- Limiting water ingress to reduce expansion, contraction and warping
- Preventing deterioration caused by insects, mould and fungi
There are also claims that yakisugi, can reduce thermal conductivity and that the resins in the charred layer protect the residual wood from flame. Some research claims the process has minimal impact on fire retardancy, others have evidenced a slower ignition time. As there is no conclusive answer, we are often asked if Shou Sugi Ban® charred timbers are fire rated.
Is Shou Sugi Ban® Fire Rated?
Whether the yakisugi preservation technique reduces flammability or not, charring does not provide sufficient fire protection to be compliant with UK or EU building regulations.
Firstly, it is important to note that not all timbers are suitable for charred cladding or construction. In Japan, where we learnt this skill, Red Cedar is widely used. We have researched, tried and tested a range of sustainably sourced hardwoods and softwoods to select those which are sufficiently strong and durable for habitable buildings.
Each timber is handcrafted by our on-site team, who are experienced in using the traditional controlled charring process. Then, they apply an additional treatment to all ShouSugi Ban® timbers that are used for construction or cladding. Our certified fire rated timbers are independently tested to ensure they meet or exceed building regulation standards.
In providing a compliant solution, we have satisfied architects, building developers and homeowners to embrace the aesthetic beauty and natural preservation of Shou Sugi Ban®. They have specified our charred timbers to provide the desired finish to a wide range of projects including:
- Inspired Contemporary Homes
- Ambitious Public Spaces
- Expansive Barn conversions
- Stylish Garden Offices
- Impactful Building Renovations
Fire retardancy is just one of a range of coating and finishing options to maximise performance and minimise the maintenance of Shou Sugi Ban®. Our job is to ensure that our premium charred timbers are suitable for external and internal applications and can stand the test of time.
If you need fire rated Shou Sugi Ban® or would like to discuss other finish options, please get in touch 01494 711800 and talk to us. We are happy to advise on the suitability of different timbers, finishes and applications for your project.
The Importance of Professional Installation
We do all we can to supply premium timber cladding, however, the wider integrity & longevity of cladding also depend on professional installation. We strongly advise that Shou Sugi Ban® is handled and fitted by a fully qualified and experienced installation team.
We provide storage, handling and installation advice to help minimise surface damage and provide appropriate drainage and ventilation. In addition, we supply professional finishes to treat sawn edges.
Regular maintenance also supports the long term durability and visual impact of charred timbers. We recommend an annual brush to remove dirt and cobwebs. A reapplication of coatings or finishes is also required, we will advise on the frequency based on the timbers selected for your project.
When installation and maintenance advice is followed and the work is completed to a high standard, Shou Sugi Ban® timbers provide a long lasting and stunning finish to any building.
Research into the flammability of pre-charred timbers: https://www.sciencedirect.com/science/article/abs/pii/S0379711223000139