Last edited 13 Jan 2019


The term ‘combustibility’ refers to the tendency of a substance to burn as a result of fire or chemical reaction. It is can be expressed as a property that is a measure of how easily a substance will ignite or burn, an important consideration when materials are being used or stored for construction purposes.

The term ‘flammable’ may be used to describe substances that ignite more easily, whilst substances that are harder to ignite or that burn less intensely may be referred to as combustible.

Less combustible materials may be described as 'materials of limited combustibility'. Approved document B of the building regulations defines limited combustibility as: 'a material performance specification that includes non-combustible materials, and for which the relevant test criteria are set out in Appendix A, paragraph 9.'

Approved document J, Combustion appliances and fuel storage systems defines ‘non-combustible materials’ as:

‘…the highest level of reaction to fire performance. Non-combustible materials include:

Following the Grenfell Tower Fire, a decision was taken to ban combustible materials in the cladding for buildings over 18m in height. The following change to approved document 7 came into force on 21 December 2018.

The Building Regulations restrict the use of combustible materials in the external walls of certain buildings over 18m in height. Refer to regulation 7(2) of the Building Regulations and to Approved Document B: volume 2, part B4 for details.

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