[Building Surveying] Did the Performance-Based Fire Code Cause the Grenfell Fire?

8 min readDec 28, 2024

One of the root causes of the Grenfell Fire 2017 was the use of a combustible external cladding system, specifically aluminium composite material (ACM) panels with a polyethylene core, which was highly flammable and acted as a primary fuel for the rapid spread of the fire. However, the cladding of the Tower was certified to Class 0 by the British Board of Agrément, which was an accepted solution to the fire performance requirements. Thus, the question is why would the UK regulations allow the use of combustible materials for external wall cladding?

It is related to the complications introduced by the performance-based fire code, even if it wasn’t solely to blame (Grenfell Tower Inquiry, 2024).

Introduction of Performance-Based Fire Code

In 1985, the UK introduced the Building Regulations 1985, marking a shift from fully prescriptive rules to a performance-based fire code, allowing alternative methods to meet fire safety objectives. The 1991 revisions to Approved Document B expanded this approach, enabling greater flexibility by permitting compliance through fire engineering solutions and testing standards like Class 0 and BS 8414. By the 2000s, deregulation further reduced oversight, increasing reliance on self-certification and creating opportunities for cost-cutting and misinterpretation of fire safety requirements.

Section B4 of Approved Document B (ADB) of the Building Regulations 2010 for England and Wales addressed the external fire spread of buildings. Appendix A of ADB outlined the requirements for fire performance of materials. It required external cladding materials to demonstrate compliance either through:

Achieving Class 0 certification under the UK standards (BS 476), or
Meeting the requirements of limited combustibility via European or British fire testing standards.

However, the two compliance routes are not equivalent. Many stakeholders opted for the easier and cheaper Class 0 route, bypassing rigorous fire performance testing required for materials deemed “limited combustibility.”

Two Incompatible Compliance Routes

In the earliest version of ADB (2002), there was no such incompatibility issue as Para. 13.7 of the ADB (2002) required “limited combustibility” of external wall construction, and explicitly warned that satisfying the provisions in Diagram 40 could not be accepted as satisfying “limited combustibility”:

“External wall construction
The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials for cladding framework, or of combustible thermal insulation as an overcladding or in ventilated cavities, may present such a risk in tall buildings, even though the provisions for external surfaces in Diagram 40 may have been satisfied.
In a building with a storey 18m or more above ground level, insulation material used in ventilated cavities in the external wall construction should be of limited combustibility (see Appendix A). …” (7.123, Grenfell Tower Inquiry, 2024)

However, the 2006 version of ADB re-worded Para. 13.7 to Para. 12.7 to the effect that the warning was removed:

“Insulation Materials/Products
In a building with a storey 18m or more above ground level any insulation product, filler material (not including gaskets, sealants and similar) etc. used in the external wall construction should be of limited combustibility (see Appendix A).” (7.129, Grenfell Tower Inquiry, 2024)

This simplified version introduced the incompatibility. First, it removed the warning of satisfying Diagram 40. Second, it required “limited combustibility” for insulation product, filler material etc. used in the external wall construction.

Diagram 40 and the incompatibility

The previous ADB said, “the external surfaces of walls should meet the provisions in Diagram 40.” Diagram 40 in Approved Document B (ADB) showed in the legends that Class 0 or Class B or better as the applicable standard for external surfaces or walls of any buildings taller than or equal to 18m :

Class 0 (National class) or Class B-s3, d2 or better (European class)

It seems that the two routes were considered equivalent by the authority before the Grenfell fire, but in fact they are completely different.

Class 0 (National class): Refers to the British standard BS 476, where Class 0 is a national classification, meaning a material has passed BS 476 Part 6 (Fire propagation) and BS 476 Part 7 (Surface spread of flame).
Class B-s3, d2 or better (European class): Refers to the European standard EN 13501–1, which classifies materials based on their reaction to fire.

Rockpanel (nd.) highlights the key differences between Class 0 and Euroclass B as follows:

All too often, Class 0 is being compared to Euroclass B, because both are mentioned in existing regulations. However, Class 0 is not, and can never be, comparable to a Euroclass system Class B. Two different conditions are measured here: National Class 0 measures the spread of flame and the amount of heat release from the surface of a product.
The Euroclass system measures (via sbi-tests, Single Burning Item) flame spread, ignitability, amount of heat, smoke & toxic gas release, whether the product melts, drips or chars. This is more important, because the Euroclass system focuses on the combustibility of materials, not (just) the spread of flames. It is possible that a product, classified as Euroclass B, also has the characteristics of a Class 0 product, but never the other way around.

ADB Updated to Require Class A2

The Class 0 route was not removed until one year after the Grenfell fire, even though “the government was told to update ADB” after an earlier fire, the Lakanal House fire in 2009, that killed six people (Apps, 2018). Finally, on 19 July 2018, a new draft version of ADB, that removed Class 0 route and upgraded to Class A2, was released:

The new document drops a previous paragraph which permitted materials with a fire rating of ‘Class B’ or ‘Class 0’ to be used on the ‘external surface’ of tall buildings. Instead, it now says that all materials used on the external walls of high rises should meet the higher standard of ‘Class A2’ or better.

Findings of the Grenfell Tower Inquiry

The combustibility of ACM has been known to the government not later than 2002.

‘One of the four products that did achieve Class 0 in BRE’s tests was a panel described in its report as an “aluminium sheet”, …When subjected to a full-scale test, a system incorporating panels of that kind reached the failure criteria in Fire Note 9 at a very early stage, exceeding the external temperature limits within three minutes of the start and the internal limits after 4.34 minutes’ (7.79, Grenfell Tower Inquiry, 2024)
‘Nonetheless, in its report dated 16 September 2002 BRE said only that the aluminium sheet product had satisfied Class 0 but had proved to be one of the worst performing products in the intermediate scale and Single Burning Item tests. It concluded by saying that, as the current guidance in Approved Document B asked for Class 0 performance in Diagram 40, those matters might require further consideration. That was as far as the report went.’ (7.82, Grenfell Tower Inquiry, 2024)

This event clearly implied that the authority (BRE) obtained first-hand data, not later than 2002, of the incompatibility between the Class 0 requirement in Diagram 40 and the ‘limited combustibility’ requirement in the Class B requirement. Unfortunately, they did not remove the Class 0 equivalence until after the Grenfell fire.

“There is no evidence of any discussions within the department about withdrawing Diagram 40 (and thus Class 0) as a relevant standard for the fire performance of the external surfaces of high-rise buildings” (7.89, Grenfell Tower Inquiry, 2024)
“One might reasonably question whether Mr Burd or anyone else in the department, including Mr Martin, studied the BRE report in any detail or really gave any thought to the implications of the results of the full-scale test using the ACM product. If they had done so, they would surely have realised that although it had a Class 0 surface, it was highly combustible and entirely unsuitable for use on the external walls of buildings, particularly high-rise buildings.” (7.90, Grenfell Tower Inquiry, 2024)

The crux is when a conflict is resulted between the regulations (functional requirements) and the Approved Document B (guidance of acceptable solutions), then which one should prevail?

The Inquiry found that the authority tended to argue that the functional requirements prevail:

“Mr Burd’s view at the time was that the use of ACM panels on buildings over 18 metres in height did not comply with functional requirement B4(1) of the Building Regulations. In his view, the general warning in paragraph 13.7 of Approved Document B against the use of combustible materials and the existence of functional requirement B4(1) were sufficient to prevent the use of such products on high-rise buildings.” (7.90, Grenfell Tower Inquiry, 2024)
“Brian Martin also thought that, although Diagram 40 allowed the use of ACM panels with a Class 0 surface to be used on buildings over 18 metres in height, their use would contravene functional requirement B4(1) of the Building Regulations, but he could not explain why Approved Document B contained guidance that appeared to allow the use of a product that would result in a breach of the Building Regulations.” (7.91, Grenfell Tower Inquiry, 2024)

However, the Inquiry Panel did not seem to agree with the arguments. The ADB contents provide prescriptive-based acceptable solutions that the designs would be accepted:

“On any view, that created a deeply unsatisfactory position for at least two reasons: first, because following the guidance is evidence of compliance with the requirements of the Building Regulations and, secondly, because although the contents of Approved Document B are no more than guidance, their detailed nature encourages people in the construction industry to treat them as prescriptive and not to pay sufficient attention to the functional requirements themselves. If the department thought that the use of some cladding panels with Class 0 surfaces did not comply with the Building Regulations, it should have given urgent thought to withdrawing Class 0 as a standard or at least to including in Approved Document B an explicit warning about the use of composite products, substantial parts of which were combustible.” (7.91, Grenfell Tower Inquiry, 2024)

Conclusions

The performance-based fire code required demonstration of the fire safety of external cladding by a full scale fire test such as BS 8414. Yet, the ADB provides two incompatible prescriptive-based acceptable solutions, namely, (a) Class 0 national class or (b) Class B Euroclass. That was one of the major causes of the Grenfell fire established by the Grenfell Tower Inquiry (2024). Combustible materials of Class 0 were used for the refurbishment of the Grenfell Tower. Unfortunately, the inquiry could not identify the reasons why Class 0 was mistakenly considered equivalent to Class B.

One year after the Grenfell fire, the ADB has been updated to require Class A2 materials for external cladding.

References:

Apps, P. (2018). Government removes passage blamed for cladding crisis from new draft guidance. Inside Housing, 19 July. https://www.insidehousing.co.uk/news/government-removes-passage-blamed-for-cladding-crisis-from-new-draft-guidance-57282

Rockpanel (nd.) Class 0 is a no-go for fire safety of high-rise buildings. https://www.rockpanel.co.uk/product-benefits/firesafety/class-0/

Grenfell Tower Inquiry (2024) Grenfell Fire Report — Stage 2. https://www.grenfelltowerinquiry.org.uk/phase-2-report