Chapter 6: Regulations and guidance relating to external walls

Introduction

¶6.1 Legislative involvement in the construction of external walls has its origin in the Great Fire of London, 1666. For many years prescriptive rules contained in local Acts of Parliament and byelaws determined the kinds of materials and methods of construction that could be used, but during the latter half of the last century there was a move towards reliance on functional requirements of a kind that were capable of being applied in accordance with the nature, location and use of the particular building. The regulations were supported by statutory guidance contained in a series of approved documents.

¶6.2 Our survey of the development of the regulatory framework relating to the construction of external walls reveals the extent to which restrictions on the use of non-combustible materials were relaxed by degrees to permit the use of combustible materials in certain circumstances. The relaxation of the requirements was accompanied by an increasing lack of clarity in the language of the regulations and associated guidance. Over time, certain definitions (including the definition of national Class 0) were altered in a way that rendered them unclear. Both developments are important in explaining the environment in which the building profession was operating when the refurbishment of Grenfell Tower was undertaken between 2012 and 2016.

¶6.3 In the chapters that follow we have sought to put the most important of those changes into context and to explain the reasons why they were made, insofar as the evidence permits us to do so. We have begun our survey with the fire at Knowsley Heights in Liverpool in 1991 because it seems to us that the events that followed laid the ground for the tragedy which occurred at Grenfell Tower in June 2017.

The London Building (Constructional) By-laws

¶6.4 At the time Grenfell Tower was built London had its own system of building legislation, principally the London Building Acts 1930–39 and associated byelaws. The London Building (Constructional) Amending By-laws (No. 1) 1964 provided that all elements of construction were to be non-combustible, but a specific byelaw permitted external cladding to be made of such materials, of such thicknesses and fixed and supported in such a manner as the District Surveyor might approve.

¶6.5 In March 1973 all existing byelaws were revoked by the London Building (Constructional) By-laws 1972. The 1972 byelaws required the construction to be non-combustible, but any external cladding could either satisfy the requirements of the District Surveyor or comprise 1mm of combustible material applied to a non-combustible backing, such that the composite material would achieve a Class 1 surface spread of flame if tested in accordance with BS 476-7.²⁴⁶²⁴⁶ Todd {CTAR00000001/28} paragraph 4.1.16.

¶6.6 It is clear, therefore, that by 1973 the London byelaws not only drew a distinction between the construction of the external wall and external cladding but also permitted a thin layer of combustible material to be used as the surface of any external cladding provided that the composite product met certain requirements in relation to the surface spread of flame.

The 1965 Building Regulations

¶6.7 A similar approach was taken in the Building Regulations 1965 (which did not apply to Inner London). The 1965 Regulations provided that any external wall of a building exceeding 50 feet in height should not include any combustible material except any external cladding not required by paragraph (3) to be non-combustible.²⁴⁷²⁴⁷ Regulation E7(2)(b)(i) {INQ00015096/42}; Lane, Expert witness presentation - 10 November 2020: https://www. grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10-november-2020, Part 2, page 103

¶6.8 By paragraph (3), any cladding on an external wall situated more than three feet from a relevant boundary, if the building was more than 50 feet²⁴⁸²⁴⁸ 50 feet is 15.24 metres. in height, was required to have a surface complying with the requirements for Class 0, save that cladding below 50 feet could consist of timber of 3/8in finished thickness. That was the first time that Class 0 had been introduced into the regulatory regime in England and Wales. By regulation E14, in order for the surface to be of Class 0 the material had to be non-combustible throughout or

"comprise a base or background which is non-combustible with the addition of a surface not exceeding 1/32 inch thick so that the spread of flame rating of the combined product is not lower than Class 1 in clause 7 of … [BS 476:7]; or comprise a base or background which is combustible but with any exposed face finished with a layer not less than 1/8 inch [3.175mm] thick of non-combustible material and with the other face not exposed to air."²⁴⁹²⁴⁹ Regulation E14 {INQ00015096/50-51}; Lane, Expert witness presentation - 10 November 2020: https://www. grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10-november-2020, Part 2, page 104; Bisby, Regulatory Testing and the Path to Grenfell Report {LBYP20000001/69-71} paragraphs 325-335.

¶6.9 It is apparent, therefore, that the 1965 Regulations drew a distinction between the external wall and "cladding". They also permitted the use of external cladding with a very thin surface layer of combustible material, provided the panel as a whole achieved a Class 1 surface spread of flame rating when tested in accordance with what is now BS 476-7. The regulations also permitted cladding which consisted of a combustible "base or background", provided that any exposed face was finished with a 1/8in thick layer of non‑combustible material.

¶6.10 The 1965 Building Regulations also expressly provided that any reference to the "surface of a wall" should be construed as a reference to that surface excluding any door, door frame, window or window frame.²⁵⁰²⁵⁰ Regulation 14(4)(e) {INQ00015096/51}. Taken together with the Class 0 definition, there was no room for doubt about what constituted the "surface" for the purposes of the external cladding requirements, and specific thicknesses and descriptions were prescribed for external cladding so that there was no ambiguity about what type of cladding was permitted and what was not. As we will see, that clarity was lost in later guidance provided in Approved Document B.

The Building Regulations 1972

¶6.11 The Building Regulations 1972 retained the requirement for the external wall of a building over 15 metres²⁵¹²⁵¹ Metric units of height replaced imperial. in height to be non-combustible and any external cladding to be classified Class 0.²⁵²²⁵² Regulation E7(2)(a)(i) of the Building Regulations 1972; Lane, Expert witness presentation - 10 November 2020: https://www.grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10-november-2020, Part 2, page 107. However the definition of Class 0 was changed to refer to materials which were non-combustible "throughout" or which had a surface material which, when tested in accordance with BS 476-6, achieved a fire propagation index (I) not exceeding 12 and a sub-index (i) not exceeding 6.²⁵³²⁵³ Regulation E15(1)(e) of the Building Regulations 1972.

¶6.12 The 1972 Regulations also made it clear that if the surface material were bonded to a substrate, the surface material in conjunction with the substrate had to achieve that level of performance.²⁵⁴²⁵⁴ Regulation E15(1)(e)(ii) of the Building Regulations 1972. The definition of "surface" remained the same as in the 1965 Regulations.²⁵⁵²⁵⁵ In Regulation E15(b). The provision in the 1965 Regulations that a combustible substrate with a non-combustible surface could be rated Class 0 was not retained in the 1972 Regulations.

¶6.13 As Professor Bisby has explained, those who developed the BS 476-6 method to test fire propagation appear to have been satisfied, based on the (limited) experimental data they had at the time, that a fire propagation index (I) of less than 12 indicated a lower hazard, whilst a fire propagation index above 20 indicated the highest possible hazard.²⁵⁶²⁵⁶ Bisby, Regulatory Testing and the Path to Grenfell Report {LBYP20000001/78} paragraph 375. That was based on comparing the performance of products in the BS 476-6 test with how they performed in small-scale compartment fire tests.²⁵⁷²⁵⁷ Bisby, Regulatory Testing and the Path to Grenfell Report {LBYP20000001/77} paragraphs 373-374.

The Building Regulations 1976

¶6.14 In the Building Regulations 1976 the position remained the same,²⁵⁸²⁵⁸ Regulation E7(3)(a) and (4) of the Building Regulations 1976; Lane, Expert witness presentation - 10 November 2020: https://www.grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10-november-2020, Part 2, page 120. save that the definition of Class 0 was changed again. Class 0 was defined either as non-combustible throughout, or by reference to a surface material which was tested both to BS 476-7 on surface spread of flame and BS 476-6 on fire propagation.²⁵⁹²⁵⁹ Regulation E15 (1)(e)(ii) of the Building Regulations 1976; Lane, Expert witness presentation - 10 November 2020: https://www.grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10- november-2020, Part 2, page 120; Bisby, Regulatory Testing and the Path to Grenfell Report {LBYP20000001/79} paragraphs 380-383. Again, the regulations made clear that if the surface material was bonded to a substrate, the surface material in conjunction with the substrate had to achieve that level of performance.²⁶⁰²⁶⁰ Regulation E15(1)(e)(ii).

¶6.15 This reliance on tests according to both BS 476-7 and BS 476-6 to establish Class 0 remained essentially unchanged until the Grenfell Tower fire in 2017.

Building Regulations 1985 and Approved Document B 1985

¶6.16 Following the introduction of the Building Act 1984 and the Building Regulations 1985, all technical requirements were eliminated from the regulations themselves. Instead the regulations were cast in the form of functional requirements supported by approved documents which gave practical guidance on the means by which the functional requirements could be achieved.²⁶¹²⁶¹ See Chapter 4.

¶6.17 Section 7(1) of the Building Act 1984 provides that, in any civil or criminal proceedings, if it is alleged that a person contravened a provision of the Building Regulations, proof of compliance with an Approved Document may be relied on as tending to negative liability and a failure to comply with an Approved Document may be relied on as tending to establish liability. Its effect has been greater than may have originally been envisaged, because it has led many involved in the construction industry, including designers, contractors and building control officers, to treat the guidance in the Approved Documents as prescriptive, thereby making it unnecessary to worry about the functional requirement itself. As we shall see when we come to the history of Approved Document B, some designers and contractors set out not to satisfy the functional requirements themselves but simply to follow the Approved Documents. Some of those who acted in that way may have been motivated by a cynical desire to obtain the benefit of section 7(1), regardless of whether the functional requirement was in fact satisfied, but we suspect that many more, including many building control officers, simply felt more comfortable working within a prescriptive regime and regarded the Approved Documents as providing it.

¶6.18 Whatever the reason may have been, contractors, designers and consultants generally soon began to regard compliance with the Approved Documents as tantamount to compliance with the Building Regulations themselves.²⁶²²⁶² Todd {CTAR00000001/52} paragraph 5.2.5(ii). Section 7 thus encouraged the industry generally to place more importance on complying with the Approved Documents, and thereby obtain the benefit of section 7(1), than on compliance with the Building Regulations themselves. The Approved Documents thus became a de facto prescriptive code.

¶6.19 Functional requirement B4(1) of the Building Regulations 1985 relating to the spread of fire over external walls provided that "The external walls of the building shall offer adequate resistance to the spread of fire over the walls…"²⁶³²⁶³ {INQ00015097/13}.

¶6.20 In Approved Document B 1985 dealing with fire safety, the longstanding requirement in the Building Regulations that external walls should be non-combustible was changed to provide that all external walls should be constructed of materials of limited combustibility if the building was more than 15 metres in height²⁶⁴²⁶⁴ {CLG10002325/15} paragraph 2.7; Lane, Expert witness presentation - 10 November 2020: https://www. grenfelltowerinquiry.org.uk/hearings/expert-witness-presentation-dr-barbara-lane-10-november-2020, Part 2, page 109; Todd {CTAR00000001/52} paragraph 5.2.5(ii). and the BS 476-11 test was introduced as a method of testing to that standard.²⁶⁵²⁶⁵ Under "Materials of limited combustibility" Appendix A, paragraph A13 {CLG10002325/50} and Table A7 at {CLG10002325/51}; Bisby, Regulatory Testing and the Path to Grenfell Report {LBYP20000001/86} paragraph 413.

¶6.21 In addition, in the case of buildings over 15 metres in height, any cladding at a height of 15 metres or more above the ground could be combustible if it was not being relied on to contribute to the fire resistance of the wall and satisfied Class 0.²⁶⁶²⁶⁶ {CLG10002325/15} paragraphs 2.9, 2.13 and Table 2.2. However the definition of Class 0, which was now also set out in the Approved Document, was changed again. The description of Class 0 to be found in Appendix A of the Approved Document B under the heading "Walls and Ceiling Linings (etc)", was as follows:

"Class 0 which restricts both the spread of flame across a surface and also the rate at which heat is released from it, imposes a more strict control than Class 1. Class 0 is not a classification identified in a British standard test, and is considered a higher class than Class 1. A Class 0 material or the surface of a composite product is either: (a) composed throughout of materials of limited combustibility, or (b) a Class 1 material which has a fire propagation index (I) of no more than 12, and (i) of not more than 6."²⁶⁷²⁶⁷ {CLG10002325/49} Appendix A at paragraphs A7 and A8.

¶6.22 The definition of Class 0 therefore changed in two important ways when Approved Document B was first introduced. First, a requirement that materials or surfaces of materials should be of limited combustibility was introduced in place of the requirement that they be composed of non-combustible materials; secondly, the requirement to consider the substrate and the surface of a composite product together was removed. As a result, the definition of Class 0 no longer made it clear that any test of a composite product had to be carried out on the surface in conjunction with its substrate. To many that might have appeared self-evident, but in the absence of any clear statement to that effect the reader might be led to think that a composite product with a combustible core could be rated Class 0 provided that its surface was a material of limited combustibility, regardless of whether or how the composite product had been tested.

¶6.23 However, the reference in the alternative requirements to testing in accordance with both BS 476-6 and BS 476-7 remained unchanged.

¶6.24 A summary of the guidance given in Approved Document B 1985 on the construction of external walls is set out in the following chart taken from Dr Lane's presentation.

¶Figure 6.1: Chart showing guidance on construction of external walls in ADB 1985

The Building Regulations 1991

¶6.25 The Building Regulations 1991 contained some minor amendments to the wording of the functional requirements, including functional requirement B4(1), which was amended to remove the word "adequate" so that it read "The external walls of the building shall resist the spread of fire…".²⁶⁸²⁶⁸ Todd {CTAR00000001/43-44} paragraph 5.1.28.

Approved Document B 1992

¶6.26 In the 1992 version of Approved Document B a separate performance standard for insulation was introduced for the first time. It provided that in a building with a storey at more than 20 metres above ground level, any insulation material used in the external wall construction should be of limited combustibility.²⁶⁹²⁶⁹ {BLA00005482/74} paragraph 12.7, second paragraph.

¶6.27 A general warning about the risk of fire spreading in the external envelope was also included. It provided as follows:

"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 36 may have been satisfied."²⁷⁰²⁷⁰ {BLA00005482/74} paragraph 12.7, first paragraph.

¶6.28 Diagram 36²⁷¹²⁷¹ {BLA00005482/75}. set out guidance on the construction of external walls. (It became Diagram 40 in later editions of Approved Document B.) Diagram 36 indicated that the surface of external walls of buildings over 20 metres in height (an increase from the previous 15 metres) should be Class 0. Reading the document as a whole, therefore, the reader was warned that the use of combustible materials for cladding might present a risk even though the external surface of the cladding was rated Class 0.

¶6.29 The definition of Class 0 was unchanged and again appeared under the heading "Internal linings".²⁷²²⁷² At paragraph A12 of Appendix A {BLA00005482/96}. The definition was introduced with the words "The highest product performance classification for lining materials is Class 0." Anyone reading that definition should therefore have appreciated that the primary purpose of the classification was as a performance standard for lining materials and might have questioned why that classification was being used in relation to the external surface of a building. Anthony Burd, at the time an official in DCLG, could not explain why it had been decided that a standard devised for internal lining materials had been considered appropriate for assessing the suitability of the surface of an external wall. He agreed that it was not the most suitable standard and as a result we are unable to understand how it could have been considered appropriate.²⁷³²⁷³ Burd {Day238/158:24}-{Day238/161:15}.

¶6.30 A summary of the guidance given in Approved Document B 1992 on the construction of external walls is set out in the following chart taken from Dr Lane's presentation.

¶Figure 6.2: Chart showing guidance on construction of external walls in ADB 1992

The Building Regulations (Amendment) No. 2 Regulations 1999

¶6.31 The Building Regulations (Amendment) No. 2 Regulations 1999 amended functional requirements B2, B3 and B4 by the re-introduction of the word "adequate". Functional requirement B4(1) therefore provided that external walls were adequately to resist the spread of fire over the walls.²⁷⁴²⁷⁴ Todd {CTAR00000001/45-46} paragraph 5.1.35 (iii).

Building Regulations 2000 and Approved Document B 2000

¶6.32 In the Building Regulations 2000 functional requirement B4 was unchanged, but a number of changes were made to the guidance in Approved Document B 2000.

¶6.33 First, it introduced an alternative to meeting the external wall surface classification (shown now in Diagram 40) by reference to Fire Note 9: Assessing the fire performance of external cladding systems: a test method published by BRE in 1999.²⁷⁵²⁷⁵ {INQ00014107/89} paragraph 13.5. Fire Note 9 contained a large‑scale test method which had been developed by BRE in the late 1990s as an alternative method of assessing the fire performance of an external wall.

¶6.34 Secondly, the guidance changed in a way that, if it were followed, the requirement of limited combustibility applied only to insulation used in ventilated cavities and not insulation generally.²⁷⁶²⁷⁶ {INQ00014107/89} paragraph 13.7 second paragraph. (The restriction did not apply to insulation used in a masonry cavity wall construction). The guidance also provided that advice on the use of insulation in external walls could be found in the BRE report Fire Performance of external thermal insulation for walls of multi-storey buildings BR 135 1988 (first edition).

¶6.35 Thirdly, the definition of a high-rise building was changed from 20 metres to 18 metres, for the purposes of the performance of both external surfaces and insulation.²⁷⁷²⁷⁷ {INQ00014107/89-90} paragraph 13.7 second paragraph and Diagram 40(e).

¶6.36 Importantly, the introductory text to paragraph 13.7 of Approved Document B continued to warn, in reasonably clear terms, that the use of combustible materials in the external wall might present a risk in tall buildings, even though the guidance in Diagram 40 had been satisfied.²⁷⁸²⁷⁸ {INQ00014107/89} paragraph 13.7 first paragraph. The reader should have understood, therefore, that the fact that the surface of a cladding material was rated Class 0 might not exclude the risk posed by the use of combustible materials. In other words, following the guidance in Approved Document B might not amount to compliance with the functional requirement.

¶6.37 A summary of the guidance given in Approved Document B 2000 on the construction of external walls is set out in the following chart taken from Dr Lane's presentation.

¶Figure 6.3: Chart showing guidance on construction of external walls in ADB 2000

Approved Document B 2000 with 2002 amendments

¶6.38 In Approved Document B 2000 with 2002 amendments,²⁷⁹²⁷⁹ {CLG10000740}. introduced after and as a result of the RADAR (Research on Approved Document B and Revision) project and the harmonisation exercise conducted by the government with the assistance of BRE in 2000 and 2001,²⁸⁰²⁸⁰ See Chapter 7 for the detailed analysis. the guidance on the construction of external walls was unchanged, save that the European classification system of fire performance was added as an alternative to the national system. Thus, the guidance contained in Diagram 40 was that any surface over 18 metres from the ground should be national Class 0 or European Class B-s3, d2 or better.²⁸¹²⁸¹ {CLG10000740/91}. (The references to s3, d2 mean that no limits were set for the production of smoke or flaming droplets.)

Approved Document B 2006

¶6.39 In Approved Document B 2006²⁸²²⁸² {CLG10000007}. a number of important structural and textual changes were introduced to the guidance on the construction of external walls. Paragraph 12.5 read as follows²⁸³²⁸³ {CLG10000007/95}.:

"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 in the cladding system and extensive cavities may present such a risk in tall buildings. External walls should either meet the guidance given in paragraphs 12.6 to 12.9 or meet the performance criteria given in the BRE Report Fire performance of external thermal insulation for walls of multi storey buildings (BR 135) for cladding systems using full scale test data from BS 8414-1:2002 or BS 8414-2:2005."

¶6.40 The general warning contained in the first paragraph was similar to that which had appeared in the 1992 and 2000 versions of Approved Document B, but there was now no mention of the fact that the use of combustible materials might present a risk, even though the provisions for external surfaces in Diagram 40 had been satisfied. That important warning had disappeared.

¶6.41 The second paragraph introduced an alternative way in which functional requirement B4(1) might be satisfied. Either the external wall could be constructed in accordance with the guidance set out in paragraphs 12.6-12.9 (sometimes called "the linear route"), or it could be the subject of a large-scale test in accordance with BS 8414, its performance being judged by reference to the criteria set out in BR 135 (2003, 2nd edition). In practice, that meant that combustible materials could be used in an external wall system only if the system intended to be constructed had been tested and met the performance criteria set out in BR 135.

¶6.42 The performance requirement for insulation was also changed so that it read:

"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). This restriction does not apply to masonry cavity wall construction which complies with Diagram 34 in Section 9."²⁸⁴²⁸⁴ {CLG10000007/96} paragraph 12.7.

¶6.43 In Chapter 7 below we have explained how the words "filler material…etc." found their way into this part of the guidance. We have also explained our interpretation of that wording, including our conclusion that it did not apply to the polyethylene core of the composite aluminium panels used at Grenfell Tower.

¶6.44 A summary of the guidance in Approved Document B 2006 on the construction of external walls is set out in the following chart taken from Dr Lane's presentation.

¶Figure 6.4: Chart showing guidance on construction of external walls in ADB 2006

Approved Document B 2007, 2010 and 2013

¶6.45 The guidance on the construction of external walls performance in the 2006 version of Approved Document B remained unchanged in the 2007,²⁸⁵²⁸⁵ {CLG10000005}. 2010,²⁸⁶²⁸⁶ {CLG00000161}. and 2013²⁸⁷²⁸⁷ {CLG00000224}. versions.

¶6.46 A summary of the guidance given in Approved Document B 2013 on the construction of external walls is set out in the following chart taken from Dr Lane's presentation.

¶Figure 6.5: Chart showing guidance on construction of external walls in ADB 2013

Summary of the external wall requirement/guidance changes over time

¶6.47 Dr Lane helpfully included the following table in her presentation which shows the changes in the external wall requirements as defined in the Building Regulations and subsequently in ADB through time.

¶Figure 6.6: Chart showing changes in the external wall requirements as defined in the Building Regulations and subsequently in ADB through time.