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Green Walls Fire Safety Guidance

Published on: 05/04/2024

This note gives guidance on considerations to be made when assessing compliance with Requirements B1 – B5 for both external and internal green walls.

Planning Policy is dictating the inclusion of green walls in urban locations; under the Building Regulations the compliance of approved elevational treatments under planning needs careful consideration under B4 and its potential implications under B1, B3 and B5

It is also becoming more common for internal green walls to be specified and care needs to be taken in considering their compliance with requirement B2.


Relevant Buildings Regulation 7(2)

Regulation 7(2) is prescriptive so a green wall would not be permitted in a relevant building. From 1st December 2022 hotels will be included in the definition of relevant buildings with the transition commenced by 1st June 2023 – clients with existing planning permission(s) for a Hotel(s) may wish to be made aware of this.

Other Uses

The use of Green Walls in other building types needs consideration from the design team in terms of meeting the requirements of:

  • B4
  • Fire spread over the surface of the wall
  • Impact on space separation
  • B3 – Potential bypass of compartmentation externally
  • B1 – Means of Escape – Impact on final exits
  • B5 – Fire Fighting – Impact on firefighting access

A green wall, due to its organic content and sometimes because of the planting medium used cannot achieve an A1 or A2 rating.

The Single Burn Test (EN 13823) calls for a relative humidity in the test specimen and the surface to be flat or of a regular corrugation. It is not possible for a green wall to comply to the ENs specification.  However, it is possible to carry out tests using the general EN 13823 rig and fire size. A competent fire engineer should be able to prepare an Engineered Assessment of the systems performance that can be used in assessing its compliance under the Building Regulations. (An example of an Engineered Assessment is attached; this should not be shared outside of Sweco Building Standards). These reports cannot be “extended“. Consequently, every system should be tested individually for a specific Engineered Assessment to be undertaken.

It is feasible for a system to perform at a level that would be reasonable in terms of limiting spread of fire over the surface. Surveyors should be clear that the test is not an indication of incombustibility, but how the system would react when subject to a source of ignition of 30,7 ± 2,0 kW for 20 minutes. This means substantiation would also need to consider potential sources of ignition both internal and external.

The consideration may include:

  • If the building has suppression the likelihood of the wall being subject to a breakout fire can be discounted.
  • If the building is not suppressed what would be the consequence of the wall being subject to a breakout fire which is likely to be far more intense than the 30kW fire used in the Single Burn test?
  • In these circumstances and where the building is horizontally compartmented could the green wall increase the likelihood of external fire bypassing of horizontal compartmentation?
  • In terms of external ignition, consideration should be made as to whether any green walls are vulnerable to arson due to the location/use of the building. In all cases direct pedestrian access to the wall would increase this risk of an external fire starting. Another consideration is what is the refuse storage/collection strategy for the building/area; is there a potential for volumes of refuse to be stored near the wall?

The other consideration with regards to B4 is space separation; if the narrative guidance is followed, half the area of the green wall should be counted as unprotected area. If this is the chosen design criteria by the “Fire Engineer” it can present difficulties in urban locations.  Our view is where test data is available for the proposed system a competent Fire Engineer may substantiate that the narrative guidance is too onerous.

Consideration should also be given to the green wall’s proximity to final exits/firefighting entry points; could the walls reaction to fire prejudice the exits/entries use either through propagation of the wall or falling products of combustion inhibiting their safe use?

If the proposed use of a Green Wall is considered as meeting Part B requirements, the final issue is to ensure that the “Responsible Person” is aware of the importance to maintain the wall so that it performs as tested. This acknowledgement is best sort in principle as early in the design process as possible and the “as built” and maintenance information included in the Regulation 38 pack.

Internal use

The Engineered Assessment methodology above can be used to establish the likely performance of the wall in terms of compliance with the guidance in B2. Once again if the report indicates a satisfactory level of performance, it is likely to be dependent on the maintenance of the Green Wall through out the lifetime of the building. The involvement and understanding of the “Responsible Person” through out the design process is key.

The contents of this Guidance Note are confidential to Sweco and the intended recipient and are subject to copyright in favour of Sweco. The content of this Guidance Note must not be reproduced by any person (including the intended recipient) without the prior written consent of Sweco.

The Guidance Note does not constitute professional advice and Sweco hereby offers no reliance and accepts no liability (in contract, tort (including negligence) or otherwise) for parties acting on the content of this Guidance Note without taking specific professional advice from Sweco. The Guidance Note is provided as generic guidance only and any opinion, views or advice expressed in this Guidance Note are made without any representations or provide any assurances or warranties as to the content.  If you require specific advice with respect to your own project or circumstances, please contact Neil Badley.


Example Engineered Assessment

Fire Performance of Green Roof and Walls