Are Living Walls a Fire Risk?
Living walls are becoming an increasingly important part of green infrastructure, helping to boost biodiversity in our cities, reduce air pollution, promote well-being, and lay the foundations for a more sustainable future. However, there is a concern about whether they pose a fire risk if not maintained correctly.
On June 1, 2022, the government introduced a package of measures to further strengthen and clarify building regulations and fire safety guidance as part of wider reforms to building safety. The update to Approved Document B sets clearer, stronger standards, which in turn sets limits on the combustibility of materials used in the external walls of buildings. The June 2022 update was the culmination of a series of events regarding fire safety compliance requirements for external cladding.
Numerous scientific studies confirm that living walls help to clean the air by removing significant amounts of nitrogen dioxide and trapping particulate matter, including black carbon. This can help mitigate climate change and reduce the risk of serious cardiovascular disease. Living walls can also reduce flooding by attenuating stormwater, enriching our environment through biodiversity gain, and improving the thermal performance of buildings through insulation and shading, helping to reduce the urban heat island effect. However, it’s important to consider whether this green cladding could pose a serious fire hazard if not managed It has been suggested that living walls may pose a fire hazard. Regarding fire performance, the general consensus is that as long as the green roof or wall is kept moist (typically the case to sustain the roof), it is likely to be highly resistant to ignition. However, concerns have been raised that if the green roof or wall dries out (such as during a drought without irrigation), it might present more of a fire risk. There has been limited fire testing of green roofs historically (conducted in Germany), but this does not necessarily address all potential concerns. Additionally, there is no significant fire testing of living wall systems.
The main factors to be considered in terms of fire risk are:
– How easily can the organic material ignite?
– What is the likelihood and speed of fire spreading through the organic material?
– What is the likelihood, speed, and consequences of fire spreading back into the building?
Regarding internal fire spread within a structure, there is a possibility of fire spreading over a compartment wall or across a roof into a compartment (stepped facade). Additionally, there is a risk of fire spreading across a wall facade, which could compromise compartmentation.
To comply with building regulations for green walls, the wall and ceiling linings must meet the classifications outlined in Table 10 of Approved Document B. These classifications are based on tests conducted following various parts of BS 476, which covers fire tests on building materials and structures. If a living wall system is being considered, it must be accompanied by test evidence demonstrating that it meets the relevant classification for its location within the building.
In conclusion
Best Practice Guidance states that a Living Wall used as external cladding should:
- Comply with the relevant requirements of Approved Document B; June 2022 update by undergoing independent third-party testing of the whole system including plants through whole system Engineering Assessments.
- Only include materials and plants that have undergone destructive third-party Engineering Assessments or that are demonstrably similar in nature in reaction to fire to those that have been part of full system Engineering Assessment tests as stated in the guidance.
- Include an irrigation system that has been designed, installed, and operated according to the Best Practice Guidance.
- Always have a proactive maintenance contract with a proven supplier who can demonstrate experience in ensuring continued compliance for Fire Safety.