Living walls guidance and fire testing is “inconsistent and inappropriate” says leading fire engineering academic

While outdoor so called ‘living walls’ can improve air quality and public wellbeing, Professor Ed Galea, Fire Safety Engineering Group Director at the University of Greenwich, says that the current guidance is inconsistent and not fit for purpose.

To define living walls – also known as green walls or vertical gardens – these are structures covered in living plants that can be installed onto building walls.

Speaking at the Tall Buildings Conference held alongside FIREX in May, Galea said that although external living walls undoubtedly provide improve public health and wellbeing, and introduce biodiversity to our cities, their fire safety implications mustn’t be ignored.

Credit: Chris Jones/AlamyStock

He set out examples of living wall fires, which include:

• A beer garden in Sydney in 2012 where a living wall caught fire in a semi-enclosed beer garden. When a customer used a candle to light a cigarette and one of the ferns caught fire, resulting in fire spread across the wall in a few seconds
• The Mandarin Oriental hotel in London in 2018, believed to have been caused by a by-product of arc welding landing on the felt lining of the planting façade
• A block of flats in Ealing, west London in 2018, which destroyed a living wall and decking on the 7^th floor and entered the building, damaging parts of the 7^th and 8^th floor corridors.

However, Galea said reports of living wall fires are relatively rare. It’s not clear whether this is because of the limited number of living walls around the world, the incidence of fires in living walls being rare, or the under-reporting of living wall fires because they are not treated as significant.

The risk factors of living wall components include:

• Individual materials such as plants, growth media, plastics for modules, backing layers and wood – all of which are combustible
• The spatial arrangements of materials, including gaps and air pockets in the system itself and supporting structures
• Façade designs, where, for example, the living wall abuts windows or wall penetrations and fire can spread from within to the living wall, and from the living wall to the interior of the building
• The design of the system – such as the design of the irrigation network – can affect fire spread
• A lack of maintenance leading to dry matter increasing flammability and fire spread risk
• Environmental factors such as wind and climate change

Regulatory landscape for living walls fire safety guidance

The main regulatory guidance for England on reaction to fire performance of external surfaces of walls is contained in Table 12.1 of Approved Document B (2022), where wall materials are classified in terms of reaction to fire in accordance with BS EN 13501-1:2018, the standard for reaction to fire classification of construction products.

There’s also the test for fire performance of external cladding systems, BS 8414-1, but that’s not recommended for living walls.

Best practice guidance for living walls can be found in a 2013 guidance document, Fire Performance of Green Roofs and Walls, published by the Department for Communities and Local Government.

The guidance states that living walls must comply with the requirements of Diagram 40 of Approved Document B 2013, and yet the materials must be of limited combustibility. These requirements are contradictory and were so even in 2013, said Galea. Diagram 40 suggests Class B or better, whereas page 27 of Fire Performance of Green Roofs and Walls refers to “limited combustibility” i.e. Class A2 or better.

Another issue is applying living walls to the current SBI (single burning item test under EN 13823) testing regime. Problems with SBI testing of living walls include:

• The small heat source of 30kw
• Small specimen size – the standard SBI test requires that specimen surfaces are flat or regularly corrugated, with a thickness of no more than 0.2m
• Consistency of samples of living wall – the test sample may not be representative of the original, as plants are usually trimmed to fit the test facility
• Moisture levels, as SBI testing requires certain temperature and humidity parameters

Galea said it’s also possible to ‘game’ the system by, for example, saturating the living wall before a sample is tested. “I would argue that you cannot give a Euro classification to a living thing. The alternative is a BS 8414 test which consists of a larger fire, a larger sample, and a test of the whole system.”

Galea summarised his presentation, saying:

• The fire guidance for living walls in the UK published in 2013 is outdated, inappropriate and confusing
• The current reaction to fire testing methodology using the SBI test for wet living wall systems is inappropriate
• CFD modelling has the potential to be more cost-effective than BS8414 testing but is challenging, given the complexity of living wall systems

He therefore recommended:

• The urgent update of the 2013 best practice guidance. Until the guidance document is updated, it should be removed from Approved Document B
• A modified BS 8414 test could be introduced for living walls
• To reduce the costs of BS 8414 testing, a pre-testing of living wall samples using CFD fire modelling, or a modified SBI test (with dry growth medium excluding plants and irrigation) to identify products likely to pass BS 8414 testing

Finally, said Galea, given the inherent variable nature of living walls and their associated fire properties, regular maintenance must be considered an essential component for compliance with fire safety requirements.

See Professor Galea’s full presentation here.

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