Fibre Reinforced Facade Encyclopedia: Testing and standards
Limited combustibility is a United Kingdom building regulations category for materials that are not quite non-combustible but come close, defined in Approved Document B by a set of alternative routes involving density, furnace test performance and core thickness, or by achieving Class A2-s3,d2 or better under BS EN 13501-1. It is a UK term with no equivalent in the National Construction Code, and it is regularly and wrongly used as a general description for products that are simply combustible.
Non-combustible and limited combustibility are two different categories with two different definitions, and Approved Document B uses each in different places. A material of limited combustibility is permitted where the guidance asks for limited combustibility, and is not permitted where it asks for non-combustible.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Jurisdiction | England, with equivalents in the devolved administrations | Approved Document B guidance |
| Defining document | Approved Document B, Appendix B tables of non-combustible materials and materials of limited combustibility | |
| European route | Class A2-s3,d2 or better under BS EN 13501-1 | The modern and most commonly used route |
| Density route | Material of density 1,000 kg/m³ or more meeting a BS 476-11 furnace criterion | No flaming and limited temperature rise |
| Core route | Non-combustible core at least 8 mm thick with combustible facings not more than 0.5 mm thick | Surface rating still applies where used as a lining |
| Low density route | Material below 300 kg/m³ meeting a relaxed BS 476-11 criterion | Covers mineral wool insulation |
| Non-combustible category | Class A1 under BS EN 13501-1, or the stricter BS 476-11 criterion | A separate and higher category |
| Regulation 7(2) | Requires A2-s1,d0 or A1 in external walls of relevant buildings above 18 m | Limited combustibility is not the test there |
| Australian equivalent | None | The NCC has non-combustible and nothing between |
What the category actually covers
Approved Document B sets out two tables in its appendix on performance of materials. The first defines non-combustible materials, by Class A1 to BS EN 13501-1 or by a strict BS 476-11 furnace criterion of no flaming and a temperature rise of not more than 20 degrees. The second defines materials of limited combustibility, and it is deliberately broader.
Anything already in the non-combustible table qualifies. Beyond that, a material of density 1,000 kg/m³ or more that shows no flaming and a temperature rise within the same limit when tested to BS 476-11 qualifies; so does a material below 300 kg/m³ meeting a relaxed version of that criterion, which is the route that brings mineral wool insulation into the category. A composite with a non-combustible core at least 8 millimetres thick and combustible facings not more than 0.5 millimetres thick also qualifies, though where it is used as a lining its surface rating still has to be satisfied separately. Finally, and now most commonly, a Class A2-s3,d2 or better classification under BS EN 13501-1 qualifies.
The practical content of the category is therefore materials with a small amount of organic content: plasterboard, some mineral fibre products, certain cement bonded boards and a few faced composites. It is not a home for polymers.
How it differs from non-combustible
A non-combustible material contributes no significant heat at all. A material of limited combustibility may contain organic content and may make a small contribution, bounded by the criteria above. Class A2 under EN 13501-1 captures this precisely: A1 materials are tested to EN ISO 1182 and EN ISO 1716 and must show essentially no contribution, while A2 materials are permitted a small calorific potential and are additionally tested under EN 13823, the single burning item test, to bound their contribution to a developing fire.
The consequence for a specifier is that the two terms are not synonyms and cannot be swapped in a specification. Approved Document B asks for non-combustible in some places, such as certain elements of structure and specific cavity barrier situations, and for limited combustibility in others, such as some insulation and lining applications. Writing limited combustibility into a clause that the guidance requires to be non-combustible downgrades the specification.
How the term is misused
- As a marketing phrase. Products described as of limited combustibility in sales material are frequently Class B or worse, which places them outside the category entirely.
- As a claim without a route. The category has defined routes. A claim should name one: a Class A2-s3,d2 classification with the report number, or a BS 476-11 result with the density.
- As an Australian term. The NCC has no such category. A material is non-combustible if it is Not Deemed Combustible under AS 1530.1 or on the Code’s deemed list, and otherwise it is not, whatever adjective is attached.
- As a substitute for Regulation 7(2) compliance. A2-s1,d0 is narrower than A2-s3,d2, and the smoke and droplet suffixes are not optional.
- As a system property. Limited combustibility is a material category. An external wall is an assembly, and its performance is assessed at full scale under BS 8414 against BR 135, or in Australia under AS 5113.
What this means for facade materials
A cementitious panel is the class of product that reaches the top of this hierarchy. ShapeShell-RC, the ShapeShift GRC system, carries an AS/NZS 1530.1 result of Not Deemed Combustible from Ignis Labs, which is the Australian non-combustibility classification; a UK project would need the corresponding EN 13501-1 classification from a European test.
A fibre reinforced polymer panel is neither non-combustible nor of limited combustibility. ShapeShell-RT is an FRP system, classified B-s2,d0 under EN 13501-1 by Intertek Testing Services, which places it below the A2 threshold and therefore outside both UK categories. Its route on a relevant UK building is governed by Regulation 7(2), and on buildings outside that ban by the full-scale BS 8414 route assessed against BR 135. ShapeShell-RT passed the full-scale BS 8414 and AS 5113 facade test at BRE Global, meeting all AS 5113 criteria, and holds an AS 5637 Group 1 classification from AWTA Product Testing.
Standards and references
- Approved Document B (Fire safety), England, Appendix B: non-combustible materials and materials of limited combustibility
- Regulation 7(2) of the Building Regulations 2010 (England), as amended
- BS EN 13501-1 Fire classification of construction products and building elements, Classes A1 and A2
- BS 476-11 Method for assessing the heat emission from building materials
- BS 8414 and BR 135 for full-scale external wall performance
- AS 1530.1 and NCC 2022 Volume One C2D10 for the Australian position (check the edition adopted in your jurisdiction)
Related terms
Questions specifiers ask
Is limited combustibility the same as non-combustible?
No. They are two separate Approved Document B categories with different definitions. Non-combustible is the higher category, corresponding to Class A1 or the stricter BS 476-11 criterion.
What EN class counts as limited combustibility?
Class A2-s3,d2 or better under BS EN 13501-1. Note that Regulation 7(2) for external walls of relevant buildings above 18 m requires the tighter A2-s1,d0 or Class A1.
Does the NCC recognise limited combustibility?
No. The National Construction Code has only non-combustible, evidenced by a Not Deemed Combustible result to AS 1530.1 or by the Code’s list of deemed materials.
Can FRP be of limited combustibility?
No. Fibre reinforced polymer has an organic resin matrix and cannot reach Class A2 or satisfy the BS 476-11 routes. It is classified in the B to E range under EN 13501-1.
Is mineral wool insulation a material of limited combustibility?
Typically yes, through the low density route or through a Class A1 or A2 classification, but the classification belongs to the specific product and should be evidenced by a report.
ShapeShell-RC is Not Deemed Combustible under AS/NZS 1530.1, tested by Ignis Labs; ShapeShell-RT is classified B-s2,d0 by Intertek Testing Services. See ShapeShell fire test data
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.