The LWF Blog

Fire Safety for Facilities Management Personnel – Structural Fire Protection – Part 162

August 8, 2022 11:35 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 161, LWF looked at protection against flame spread over linings. In part 162, we will discuss protecting against fire spread beyond the building of fire origin.

Working to avoid the passage of fire from one building to its neighbour is one of the oldest objectives of the building regulations, following ‘great fires’ in many cities in England and Wales. Fire spread has meant the complete destruction of large areas as fire passed from an unprotected building to the next without pause.

Official records for the great fire of London in 1666 show only 6 fatalities, however, it is likely there were hundreds and possibly thousands of victims as there are various factors likely to have contributed. For instance, to record a death in those days, a body was required and judging by the melted metal and pottery found and examined, the fire would have been hotter than a crematorium. Other factors include the terrible conditions left behind which people were living in, leading to deaths after the event but caused by it.

Given the level of destruction, it is unsurprising that methods for preventing such disasters were sought out and put into law.

In England and Wales there are two performance requirements relevant to fire spread between buildings, contained in B4 of Schedule 1 to the building regulations –

  1. The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use of and position of the building;
  2. The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building.

The first requirement requires external walls in certain circumstances to be fire-resisting and the associated external surfaces to be resistant to ignition and fire spread. Approved Document B (ADB) contains detailed recommendations for external walls, such as limits on openings and other unprotected areas to limit fire spread by radiated heat. ADB also gives recommendations for separation between buildings.

The second requirement is reflected in the detailed recommendations of ADB for roof performance construction in terms of tests carried out for British Standards to gauge the ability of the roof to resist fire penetration when its external surface is exposed to radiant heat and flame. These measurements allow classification with AA being designated for roofs with the best performance level and DD being the worst.

In part 163 of this series, LWF will begin to look at Emergency Escape Lighting. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.

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