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28 May 2020

Considerations when designing fire resistant cladding systems

Fire protection measures are classified as either active or passive. Active fire protection measures respond to the presence of a fire and includes items such as fire alarms and sprinkler systems. Passive fire protection gives protection and resistance to the building structure and the compartments within it to prevent the spread of fire.  It is the passive resistance provided by external walls that we will be discussing in this blog.

The purpose of fire resistance performance with building structures is to prevent rapid fire spread and growth that could trap occupants of the building, allow a safe means of escape and to stop spread to adjacent buildings.

Through the application of UK Building Regulations, compartmentation is seen as an integral design feature of a building so as to protect life in the event of a fire.

Almost all buildings require some compartmentation, in the form of fire-resisting walls, doors, floors, ceilings and other structural elements. Generally, however, the compartment will suppress the spread of fire only for a limited period.

When considering an external wall fire resistance depends on its distance from the relevant boundary. Separation distances are measured to boundaries to ensure that the location and design of buildings on adjoining sites have no influence on the building under construction.

The boundary that a wall faces is the relevant boundary (Diagram 13.2 in Approved Document B, below). It may be one of the following:

  1. The site boundary.
  2. The centre line of a space where further development is unlikely, such as a road, railway, canal or river.
  3. An assumed notional boundary between two buildings on the same site (Diagram 13.3 in Approved Document B, below) where either of the following conditions is met.
  1. One or both of the buildings are in the ‘residential’ or ‘assembly and recreation’ purpose groups (purpose group 1 or 5).
  2. The buildings will be operated/managed by different organisations.

fire graph1.jpg

fire graph2.jpg

Diagram reproduced from Fire Safety: Approved Document B - Building regulation in England covering fire safety matters within and around buildings.

Note: All systems above do not require internal or external lap stitching

When one or more elevations of a new building fall into the site boundary criteria above, the required design to attain the performance needed can sometimes be costly and require constructions that do not allow the external appearance of the wall in question to fit against unaffected elevations. 

The site assembled Trisobuild® systems from Tata Steel have been designed and tested independently to BS 476 part 22 to provide the specifier with fire resistance solutions to these problems.  These offer s options that provide 15, 30 and 60 minutes fire insulation resistance all with 240 minute fire integrity resistance.  These performances have been achieved through independent testing and have been optimised to provide performance levels with standard construction methods, that are not only cost effective but provide the option of many Tata Steel external profiles giving the specifier design flexibility.  See below for a summary of systems available.

fire table 3.jpg

fire build up 1.jpg


Please contact our Technical Department for further details or use our online specification tool to help you create the right specification for the performance that suits the needs of your project. Doing this will give you peace of mind that cladding components are compatible and perform together as a system.

Download our technical brochure for more information on our Trisobuild® systems

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