CROSS Safety Report
Fire safety concern over green walls
This report discusses how building close down procedures that include isolating automated water systems might result in the drying out of green walls, thus presenting a significant fire hazard in external walls.
Key Learning Outcomes
For building owners, managers and occupants:
- Be aware of the need to maintain water supplies to vegetation that does not have access to groundwater through the roots
For fire risk assessors:
- Risk assessors should be aware of this issue and when assessing buildings with this feature, advise Responsible Persons accordingly
- The Fire Safety Act 2021 clarifies that the external walls and any attachments should be considered as part of the fire risk assessment
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Green roofs and living walls are increasing in popularity. More information can be found on the Royal Horticultural Society website.
Green walls are often irrigated by an automatic timed water feed switch system. Building close down procedures that include isolating electrical/water supplies or branches might close down such a system, resulting in the drying out of the green wall and thus presenting a significant fire hazard in the external wall. If the vegetation is allowed to dry out, it may become a fuel for fire.
Guidance regarding fire safety measures has been published by HM Government and by the NFPA.
Considering external walls in fire risk assessments
External walls are not routinely covered in fire risk assessments and are not considered a separate compartment in structural fire safety terms due to the likelihood of fire spread through window openings and the weak fire performance of standard (non-fire resistant) glazing units.
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Expert Panel Comments
Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.
There is greater pressure through planning for green walls, for reasons of biodiversity, urban heat island effect and wellbeing. Planning will often require the maintenance of the planting, for visual reasons, but when approving for building regulations irrigation is a critical factor.
Any system which is important to safety needs to have appropriate measures in place to allow for maintenance, or for breakdown. It is probably not currently on people's radar that irrigation may fall under the same category as sprinklers or fire alarms, so fire strategies and fire risk assessments need to reflect its importance.