An Overview Of BRoofT4


Flat Roofing – An overview of BRoof(T4)

Fire safety and performance of materials in relation to fire has always been of upmost importance when designing and constructing any building project, however, following the Grenfell disaster in 2017, both the government and the construction industry have put an increased focus on fire safety, including the fire risks present in flat roof build ups.

In 2019 (and subsequently updated in 2020 and 2022) ‘Fire Safety-Approved Document B’ (AD B) was put into force with the help of multiple trade bodies (LWRA, SPRA & NFRC) working closely with the government. Alongside the changes, the construction industry seen an increased awareness of fire compliance.

Within this document, the requirements for roofs of a building are set out to ensure the areas are constructed to adequately resist the spread of fire, including the spread from one building to another. One important change from the previous editions of the document, is that the European Classification system set out in BS EN 13501-5, that has run alongside the National Classification system (BS 476-3:2004) for many years, is now the main reference for external fire performance of roofs in the UK. This classification system has five ratings, stated below.

  • BRoof(T4)
  • CRoof(T4)
  • DRoof(T4)
  • ERoof(T4)
  • FRoof(T4)

This classification system refers to four separate tests designed to establish the performance of a roofs resistance to fire. These four test standards were required to cover the legislation in place within the various members of Europe at the time. As such, the TS 1187 has four tests for roof covering systems: t1 for Germany, t2 for Scandinavia, t3 for France and t4 for the UK (and used in the Republic of Ireland), hence the suffix ‘(t4)’ shown above. These tests measure the fire penetration and spread if such material like a burning tree branch were to fall on the roof. The result highest rating deemed as “Unrestricted and can be used anywhere on the roof” is Broof(T4). FRoof(T4) is the lowest rating of the classification.

To meet the Building Regulations for fire, the entire ‘as installed’ system must have a valid test certificate, which means that the layers within the system cannot be readily substituted with another ‘alternative’ material of different properties. The most common example we see, is the substitution of a PIR achieving a ‘E’ euroclass rating being replaced by ‘F’ rated material. For this reason, late product substitution has a risk of not achieving the results outlined in a fire certificate. If substitution needs to be made, such as dual sourcing certain insulants, this will need to be discussed with the fire certification body.

Although it is important to test as many scenarios and insulation thickness ranges as possible, there has been a lot of multiple trade body work to establish the worst-case decking for the test, with an aim to reduce the number of permutations safely. The conclusion from the multiple of bodies is that OSB is worst case decking for the test, therefore if a test is performed with OSB decking, other deck type should perform no worst.

Test 4 is very thorough and is the key test that determines a roofs performance when exposed to fire. There will be an initial test which will examine one specific sample, then three further samples will be accessed in the penetration test. The penetration test will also access a sample which includes any joint details from each layer of the roof system. The results of the test will determine which rating the tests receive, which are defined further below.

This is the highest rating of roof classification. During this test there will be no penetration of the roof system within 60 minutes. In addition, during the preliminary test, after withdrawal of the test flame, the selected specimens will burn for less than 5 minutes, and the flame spread will be less than 0.38 m across the area of burning.

During this test there will be no penetration of the roof system within 30 minutes. During the preliminary test, after withdrawal of the test flame, the specimens will burn for less than 5 minutes, and the flame spread will be less than 0.38 m across the burning region.

During the test, this roof system will be penetrated within 30 minutes, but this does not occur in the preliminary test. Instead, the specimens will burn for less than 5 minutes and have a flame spread of less than 0.38 m across the region of burning.

EROOF (t4)
During the test, this roof system is penetrated within 30 minutes but is not penetrated in the preliminary test. However, the flame spread is not controlled.

FROOF (t4)
This is the lowest rating of roof classification. No performance determined.

Referring back to Approved Document B (AD B), a balcony is referred to as a “specified attachment” and therefore requires non combustible materials throughout (with some small material exceptions such as membranes). Some confusion arose from this as the document, which is enforced by law, as it does not offer a definition between the difference between a balcony and a terrace. Therefore, some believed that all usable external roof space was classed as a balcony and therefore would be required to meet the non-combustible requirements.  Subsequently, the British standard guidance document BS 8579:2020 was created to help define the difference the two and in blunt terms, a terrace has a habitable space below it and would only need to achieve BRoof(T4) rather than having to made of non-combustible materials.

Here at TaperedPlus, we are often asked if our insulants meet BRoofT4, so that our product is suitable to be used on a usable roof or terrace. Even though TaperedPlus work in partnership with our partners to aid their testing regimes, this data would be typically held by the waterproofing manufacturer / system supplier due to the nature of the test. As described above, the test is for external fire penetration and spread of flame with the membrane being the first element in contact with the fire and the most important layer effecting the outcome of the system test.

If you would like any further guidance or information about BRoofT4, or any other technical help, please get in touch with TaperedPlus’s technical department at