Material of limited combustibility

Approved document B of the building regulations 'Fire Safety', 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.

Paragraph 9 states :

Materials of limited combustibility are defined in Table A7: a. (National classes) by reference to the method specified in BS476: Part 11:1982; or

b. (European classes) in terms of performance

When classified as class A2-S3, d2 in accordance with BS EN 13501-1:2007, Fire classification of construction products and building elements, Part 1 - Classification using data from reaction to fire tests when tested to BS EN ISO 1182:2002, Reaction to fire tests for building products - Noncombustibility test or BS EN ISO 1716:2002 Reaction to fire tests for building products - Determination of the gross calorific value and BS EN 13823:2002, Reaction to fire tests for building products - Building products excluding floorings exposed to the thermal attack by a single burning item.

Table A7 also includes composite products (such as plasterboard) which are considered acceptable and where these are exposed as linings they should also meet any appropriate flame spread rating.

Table A7 is shown below:

PAS 9980:2022, Fire risk appraisal of external wall construction and cladding of existing blocks of flats – Code of practice, published by BSI Standards Limited in 2022, defines a material of limited combustibility as either:

a) a noncombustible material or product; or
b) any material or homogenous product of density 300 kg/m3 or more, which, when tested in accordance with BS 47611, does not flame and the rise in temperature on the furnace thermocouple is not more than 20 °C; or
c) any product with a noncombustible core of 8 mm thick or more, having combustible facings (on one or both sides) not more than 0.5 mm thick; or
d) a material or product classified as Class A2s3, d2 in accordance with BS EN 135011:2018, when tested in accordance with BS EN ISO 1182 or BS EN ISO 1716 and BS EN 13823

NOTE This term is included here given its use in relation to materials used in, and standards applicable to, existing buildings. It is derived from guidance in previous versions of ADB ([10], [11], [12], [13], [14]), but this term is no longer in use in the current version of ADB ([8], [9]).