The Fifth Facade: Managing Fire Risk

When Approved Document B (ADB) was updated last year, several changes came into force which affect flat roofs, including the National Classification system being replaced by European standards. While this move has simplified classification by introducing a single BROOF(t4) rating for the UK market. it’s also sparked some confusion in the wider context of fire protection. Will Wigfield, Flat Roof Product Manager at ROCKWOOL, explains the technicalities behind the testing protocols and shares best practice advice on how to minimise fire risk in flat roofs.

The National Classification system (BS 476-3:2004) was the principle determinant of external fire performance in roofs for many years. While the European Classification system previously ran alongside it, the latest changes to ADB saw the National Classification become obsolete, with EN 13501-5 ‘Fire classification of construction products and building elements - Part 5: Classification using data from external fire exposure to roof tests’, now the main reference point for assessing fire penetration and spread of fire in external roof applications.

For roofing contractors, understanding what these changes mean in practice is crucial for ensuring relevant regulation compliance and minimising fire risk, which starts with clarifying what the new classification means in the context of fire performance.

Categorising change

Under the National Class, the highest fire performance which could be achieved was rated as AA, AB or AC - denoting that the use of a flat roof system was unrestricted and could be applied anywhere on the roof.


EN 13501-5 is now the recognised standard for indicating the performance of a flat roof system when exposed to fire from an external source. Applicable to Approved Document B, Test 4 of DD CEN/TS 1187:2012 provides the method for evaluating the performance of a roof under the conditions of thermal attack, which includes external fire spread and penetration by fire.

While the highest possible performance is classified as BROOF (t4), the equivalent of AA, AB or AC under the previous National Classification, it does not determine the reaction to fire of individual components - which means it provides no indication regarding the material’s combustibility.

A simple and straightforward way to determine the combustibility of a building product is by checking its Euroclass reaction-to-fire rating. A non-combustible material is defined by a Euroclass rating of A1 or A2-s1, d0.

Reducing risk The testing protocol of EN 13501-5 does not assess the performance of individual components. It determines how a flat roofing system - the complete build-up - will perform when exposed to an external file.

This means that BROOF (t4) cannot be used to verify the combustibility of products used within the overall system. In fact, roof systems incorporating combustible insulation products as low as Euroclass F can achieve a rating of BROOF (t4).

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