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CROSS Safety Report

Composite deck boards in common access balconies

Report ID: 1048 Published: 13 August 2021 Region: CROSS-UK

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A reporter informs CROSS that decking boards formed of a composite material contributed to external fire development in a block of flats and rendered the means of escape and firefighting access unusable.

The report relates to buildings where the access to flats is by means of an external walkway, often referred to as a common access balcony, common balcony, or a balcony/deck approach. 

Key Learning Outcomes

For designers, architects and fire engineers:

  • External walkways providing access to flats should not contribute to fire spread over an external wall and should also be protected to maintain safe escape and firefighting access
  • They must be constructed from materials that will resist fire spread, have imperforate floors, and provide at least the same fire resistance for loadbearing capacity as floors in the rest of the building to ensure stability in a fire for sufficient time to allow the safe egress of flat occupiers and access for firefighters
  • Further recommendations, including measures to control smoke spread along external walkways, are provided in BS9991:2015
  • External walkways in such buildings are also referred to as common access balconies or decks

Full Report

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The Full Report below has been submitted to CROSS and describes the reporter’s experience. The text has been edited for clarity and to ensure anonymity and confidentiality by removing any identifiable details. If you would like to know more about our secure reporting process or submit a report yourself, please visit the reporting to CROSS-UK page.


A reporter has shared information regarding a fire in a block of flats expressing concern about the use of composite decking to form the floor of the external, open sided, walkways.

Access to individual flats via a shared, external, open sided walkway is a common arrangement. In most instances the external walkway is the only means of access to a final exit, therefore the risk of fire, heat or smoke affecting the use of the walkway must be minimised. 

In the instance covered by this report, the floor of the external walkway was constructed from composite decking material. This material became involved in the fire, contributing to the spread of fire, which removed the sole means of escape for occupants of flats opening onto the walkway and the floors above and also created difficulties for firefighter access. 

Expert Panel Comments

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This is of concern as current statutory and additional guidance is very clear as to what is required when providing a common balcony or external approach, also referred to as a walkway and access balcony or deck. This is provided in Approved Document B, British Standard (BS) 9991 Fire safety in the design, management and use of residential buildings – Code of practice and supported with additional information in BS 8579:2020 Guide to the design of balconies and terraces. Section 7.3 of BS 9991 gives guidance on the design of an external balcony/deck approach to flats. Item a) states that 'the structure, including the floor, should be protected by 30 min fire-resisting construction (integrity and insulation).' Whatever type of floor construction is used for the balcony should therefore meet that standard.

It is imperative that a common balcony or external approach which provides a means of access from one part of a building to another has an appropriate level of fire resistance. This route may be required as a means of escape for occupants and access for firefighters. This is fundamental to the generally adopted stay put strategy for blocks of flats and highlights the interaction of the functional requirements of the Building Regulations (as amended), and the aforementioned guidance in support of meeting those requirements.

It is imperative that a common balcony or external approach which provides a means of access from one part of a building to another has an appropriate level of fire resistance. This route may be required as a means of escape for occupants and access for firefighters.

In this instance the reporter has not shared the actual composition of the boards, however any materials proposed to be used to form part of a common balcony or external approach, need to be confirmed as appropriate for use to meet the above requirements. For existing premises that will be in scope of The Regulatory Reform (Fire Safety) Order 2005 as clarified through the Fire Safety Act 2021, the risk posed by any such common balcony will need to be assessed as part of the premises fire risk assessment, where any doubt exists regarding applicability of the legislation then independent legal advice should be obtained.

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