Chapter 49: Industry guidance on the construction of external walls

¶49.1 In this chapter we describe the industry guidance relevant to the refurbishment of the external wall of Grenfell Tower that was publicly available from reputable sources at and around the time of the refurbishment. In addition to the guidance contained in Approved Document B, certain bodies within the construction industry published guidance on the various aspects of the construction of external walls, particularly the walls of high-rise buildings. There were important developments in that guidance, particularly between 2012 and 2017, as more became known about the performance of certain products and materials in response to fire. In some respects the guidance contained in Approved Document B was overtaken by guidance published by the industry which suggested more rigorous requirements for the fire performance of each element of any external wall. According to Dr Lane²⁹²⁹ Lane {Day61/195:1}-{Day61/197:19}.}. and Mr Sakula,³⁰³⁰ Jonathan Sakula, Report of Facade Expert {JOS00000001/34} paragraphs 8.1.1-8.1.2; {JOS00000001/35-37} paragraphs 9.2-9.4; {JOS00000001/60-61} paragraphs 17.6-17.12, Sakula {Day125/29:13-20}; {Day125/94:15}-{Day125/96:12}; {Day125/101:25}-{Day125/102:22}; {Day125/108:1-5}. knowledge of the dangers posed by the use of combustible materials was developing rapidly during that time, partly as the result of a series of fires in high-rise buildings in various countries whose external walls contained insulation made from organic materials and aluminium composite material rainscreen panels with a polyethylene core ("ACM PE panels"). Those fires and the information readily available about them are discussed in more detail in Chapter 11 of this report.

Building Research Establishment: BR 135

¶49.2 In 1988 the Building Research Establishment (BRE) published guidance entitled Fire performance of external thermal insulation for walls of multi-storey buildings.³¹³¹ See introduction to BR 135, 3rd Edition {CEL00003364/4}. It is generally known as "BR 135". The document was revised in 1999 and a second edition was published in 2003 following the fire at Garnock Court, Irvine in 1999.³²³² {BRE00005554/7}. A third edition was published in 2013.³³³³ {CEL00003364/4}. The second and third editions are relevant to the refurbishment of Grenfell Tower. BR 135 is expressly referred to in paragraph 12.5 of Approved Document B, which adopts its performance criteria using full scale test data derived from a BS 8414 test as providing one way of demonstrating compliance with functional requirement B4(1) of the Building Regulations.³⁴³⁴ {CLG00000224/95}. The history of BR 135 and the test methods contained in BS 8414‑1 (2002) and 2 (2005) are described in Chapter 5 of this report.

¶49.3 The second edition of BR 135 (2003) contained a series of important warnings about the risks posed by combustible external cladding systems. For example, Figure 2 illustrated the way in which fire may spread rapidly up through the building envelope itself to create secondary fires in compartments at many levels.³⁵³⁵ {BRE00005554/9}.

¶49.4 The guidance contained further warnings about the risks posed by external cladding systems, in particular, the risk that the existence of cavities may cause flames to become elongated and drawn up the building, possibly unseen,³⁶³⁶ {BRE00005554/10}. to affect several stories simultaneously and how fire can spread unseen through cavities,³⁷³⁷ {BRE00005554/17}. thus making firefighting more difficult.³⁸³⁸ {BRE00005554/10}. The guidance also referred to the fact that non-combustible materials were typically used in such systems as it was difficult to prevent fire entering the cavity and spreading through the insulating material.³⁹³⁹ {BRE00005554/17}. It also warned that, if exposed directly to the sustained flame envelope, metal panels, such as aluminium, might melt, generating molten debris.⁴⁰⁴⁰ {BRE00005554/17-18}.

¶49.5 The third edition of BR 135 (2013) repeated the warnings given in the second edition⁴¹⁴¹ {CEL00003364} see e.g. paragraphs 3.3.2 and 3.5. and contained further warnings about external fire spread and the use of certain materials in cladding systems. In particular, it drew attention to the rapid development of the market for cladding systems, driven by the need to construct more energy-efficient and sustainable buildings, which had resulted in increased volumes of potentially combustible materials being used in external cladding applications.⁴²⁴² {CEL00003364/11} paragraph 2.1. There were further important warnings about the proper use of cavity barriers and fire-stopping. The warnings about insulation and cladding panels were also more detailed. In particular, on the subject of cladding panels it said:

"These products generally have good surface spread of flame characteristics to prevent rapid fire spread across the surface of the system, but once the panels become involved in the fire, they have the potential to generate falling debris, add to the overall fire load, and provide a route for fire to propagate up the outside of the building"⁴³⁴³ {CEL00003364/22} paragraph 6.4.1.

Building Control Alliance

¶49.6 The Building Control Alliance ('BCA') was formed in 2008 to represent the interests of those involved in carrying out building control functions, both local authorities and approved inspectors, and to promote consistency in the interpretation of the Building Regulations and statutory guidance. From time to time its Technical Group published guidance notes intended to assist building control officers in carrying out their functions.

¶49.7 In June 2014 BCA produced version 0 of its Technical Guidance Note 18 entitled Use of Combustible Cladding Materials on Residential Buildings (TGN 18).⁴⁴⁴⁴ {CEP00057294} The purpose of the note is described as follows: "BCA technical guidance notes are for the benefits of its members and the construction industry, to provide information, promote good practice and encourage consistency of interpretation for the benefit of our clients. They are advisory in nature, and in all cases the responsibility for determining compliance with the Building Regulations remains with the building control body concerned."Show full note The introduction to TGN 18 stated that the note outlined the procedures referred to in paragraph 12.5 of Approved Document B for demonstrating compliance with functional requirement B4(1) and set out to address common misconceptions relating to combustibility and surface spread of flame ratings.⁴⁵⁴⁵ {CEP00057294/1}.

¶49.8 Under the heading "Key Issues", TGN 18 stated that the spread of fire by way of the external wall is exacerbated by the use of combustible materials and extensive cavities. It warned that within the confines of a cavity, flames can elongate up to ten times in search of oxygen, meaning that there is a need for robust cavity barriers, restricted combustibility of key components and the use of materials with a low spread of flame rating.⁴⁶⁴⁶ {CEP00057294/1}.

¶49.9 Importantly, TGN18 made it clear that a surface spread of flame classification does not indicate that the material is not combustible. It went on to state that:

"Thermosetting insulants (rigid polyurethane foam boards) do not meet the limited combustibility requirements of AD B2 Table A7 and so should not be accepted as meeting AD B2 paragraph 12.7. However, if they are included as part of a cladding system being tested to BR135 & BS8414, the complete assembly may ultimately prove to be acceptable. The BR135 / BS8414 tests deal solely with the spread of fire once it has entered the cavity. Hence, the requirements for cavity barriers in accordance with Section 9 of AD B2 are required in all cases including around openings in the façade."⁴⁷⁴⁷ {CEP00057294/1}.

¶49.10 TGN 18 went on to recommend three options for demonstrating compliance with paragraph 12.7 of Approved Document B.⁴⁸⁴⁸ {CEP00057294/2}. Option 1 was the use of materials of limited combustibility for all elements of the cladding system both above and below 18 metres. Option 2 was to demonstrate that the entire system met the performance criteria in BR 135 when tested in accordance with BS 8414. Option 3 was to submit a desktop study report from "a suitable independent UKAS accredited testing body" based on test data already in its possession stating whether, in its opinion, the proposed system would meet the criteria in BR 135. As far as we are aware, that was the first occasion on which it had been formally suggested that a desktop study could provide a means of demonstrating compliance with functional requirement B4(1). It was not referred to in Approved Document B and was not the method adopted in connection with the refurbishment of Grenfell Tower.

¶49.11 A further edition of TGN 18 (version 1) published in July 2015 contained similar warnings about external fire spread.⁴⁹⁴⁹ {CEL00002347}. This revised guidance made it clear that a wider group of thermosetting insulants did not meet the limited combustibility requirements of Approved Document B Table A7, including polyisocyanurate and polystyrene foam boards. When dealing with desktop study reports the guidance now said that a report from a "suitably qualified fire specialist" based on test data from a suitable independent UKAS accredited testing body was acceptable, without indicating what qualifications might be required for the purpose. The effect of that change was to increase the number of persons who might be considered suitable to carry out such a study. This version also introduced a fourth option in the form of a "holistic fire-engineered approach" taking into account "the building geometry, ignition risk and factors restricting fire spread etc."⁵⁰⁵⁰ {CEL00002347/2}. That method was not adopted in connection with the refurbishment of Grenfell Tower.

Centre for Windows and Cladding Technology

¶49.12 The Centre for Windows and Cladding Technology (CWCT) is an industry body comprising a broad spectrum of clients, architects, consultants, contractors, manufacturers and researchers which exists to assist its members in the construction of building envelopes and glazing.⁵¹⁵¹ https://www.cwct.co.uk/pages/about-us. From time to time it publishes recommended standards and guidance for the benefit of its members and hosts meetings to discuss matters of interest to the industry. In the period 1996 to 2018, CWCT produced five documents of relevance to the Inquiry's investigations: Guide to Good Practice for Facades, 1996;⁵²⁵² {CWCT0000055}. Standard for Walls with Ventilated Rainscreens, 1998;⁵³⁵³ {CWCT0000053}. Standard for Systematised Building Envelopes, 2008 ("the CWCT Standard");⁵⁴⁵⁴ {CWCT0000046}. Technical Note 73, Fire performance of curtain walls and rainscreens, March 2011;⁵⁵⁵⁵ {CWCT0000019}. and Technical Note 98, Fire performance of facades – Guide to the requirements of UK Building Regulations, 2017.⁵⁶⁵⁶ {CWCT0000024}.

¶49.13 The CWCT's Guide to Good Practice for Facades (1996) stated that thermal insulation should be inert and drew attention to the fire performance of some insulating materials.⁵⁷⁵⁷ {CWCT0000055/13} paragraph 4.10.1. The Standard for Walls with Ventilated Rainscreens (1998) made clear that any cavity behind rainscreens should not include materials which could significantly promote flame spread within the unseen cavity and therefore recommended non-combustible insulation.⁵⁸⁵⁸ {CWCT0000053/45} paragraph 2.20.4; {CWCT0000053/46} paragraph 2.20.8. It warned that the use of any combustible material for the cladding framework and insulation needed to be carefully considered as the height of the building increased.⁵⁹⁵⁹ {CWCT0000053/45} in the notes to the right of paragraph 2.20.4. Both of those CWCT standards were referred to in the structural performance specification for Grenfell Tower.⁶⁰⁶⁰ Curtins Consulting, the structural engineer appointed by the TMO, wrote a specification entitled 'Structural Performance Specification for the Design, Supply and Application of Overcladding Systems to Grenfell Tower' dated March 2013 {CCL00002347}, in which section 7.0 addressed 'Overcladding' and included reference to these standards.

¶49.14 The CWCT Standard (2008) gave guidance on a range of aspects of the construction of the external envelopes of buildings⁶¹⁶¹ {CWCT0000046/10}. Including, but not limited to, rainscreen cladding., with part 6 focusing on fire performance.⁶²⁶² {CWCT0000046/10-16}. Within part 6 the standard provided that the building envelope should not be composed of materials which readily support combustion, add significantly to the fire load, or give off toxic fumes.⁶³⁶³ {CWCT0000046/11} section 6.2. It emphasised the importance of test evidence supporting fire performance requirements, as follows:

"In all cases, products or elements of construction requiring a fire resistance or spread of flame performance should have the appropriate evidence of performance test based on test information. The final installation should follow the applicable test evidence in all respects."⁶⁴⁶⁴ {CWCT0000046/11} section 6.2. It also stated in blue italic text: "The suitability of materials should be judged in relation to their conditions of use. For example, combustible insulation may give acceptable performance when used with a metal facing…" The black text in the CWCT Standard was prescriptive, while the blue italic text gave background information or guidance on interpretation of the clause which it followed, see {CWCT0000046/6}.Show full note

¶49.15 The CWCT Standard stated that aluminium envelope systems do not normally have significant resistance to fire and that most unmodified aluminium building envelopes would provide only 10–20 minutes stability and integrity resistance.⁶⁵⁶⁵ {CWCT0000046/11} section 6.3. Under the heading "Insulation materials" it contained the same guidance as in paragraph 12.7 of Approved Document B, namely, that insulation in walls of buildings with a storey more than 18 metres above ground level should be of limited combustibility.⁶⁶⁶⁶ {CWCT0000046/15} section 6.6.2. It also made clear that cavity barriers needed to be provided to close any cavity around penetrations through the rainscreen for windows.⁶⁷⁶⁷ {CWCT0000046/14} section 6.4.4.2 (ii) under the heading "Cavities in rainscreen walls". The standard also expressly addressed "Composite components", providing:

"When one of the cladding elements is a composite of two or more materials (mechanically jointed, bonded or fused together) the elements as a whole must demonstrate the appropriate fire performance. Similarly it must be demonstrated that the composite will remain reasonably whole and not become prematurely separated from the building or framework."⁶⁸⁶⁸ {CWCT0000046/16} section 6.6.3.

¶49.16 The CWCT Standard (2008) was expressly referred to in the NBS specification for the refurbishment works at Grenfell Tower (see Chapter 56).⁶⁹⁶⁹ NBS Specification prepared by Studio E {SEA00000169/68-69} NBS Specification clauses 220/310.

¶49.17 Technical Note 73, Fire performance of curtain walls and rainscreens, was published by CWCT in March 2011.⁷⁰⁷⁰ {CWCT0000019}. It contained warnings about fire and smoke spread within cavities and out of the top of cavities and highlighted the importance of cavity barriers to close the edges of cavities, including around window openings.⁷¹⁷¹ {CWCT0000019/4-5}. Under the heading "Use of combustible material" it made it clear that "the only commonly used insulation material that will satisfy the definition of limited combustibility is mineral wool".⁷²⁷² {CWCT0000019/6}. It also emphasised that where testing was carried out in accordance with BS 8414, the test applied to the complete cladding system including insulation, rainscreen and cavity barriers⁷³⁷³ {CWCT0000019/6} under the heading "Alternative approaches". and that changing any of those components might affect the ability of the walls to resist the spread of fire.⁷⁴⁷⁴ {CWCT0000019/6}.

¶49.18 Technical Note 98 Fire performance of facades – Guide to the requirements of UK Building Regulations was published in April 2017. Although it was published too late to be taken into account in the design and construction of the refurbishment of Grenfell Tower, it provides a useful picture of the state of knowledge in the industry in the months before the fire. In particular, in the introductory section the note warnsː

"Strict compliance with ADB does not necessarily guarantee adequate performance of a given façade in a fire. It is incumbent on the building designer to ensure that the guidance given in ADB is relevant to their building and what additional measures (if any) are required to ensure the façade achieves the required performance standard."⁷⁵⁷⁵ {CWCT0000024/1}.

¶49.19 Technical Note 98 also stated that combustible materials may have non-combustible facings which restrict the spread of flame over the surface. It warned that combustible materials with non-combustible facings rely on the facings remaining intact and that the materials should be checked for damage.⁷⁶⁷⁶ {CWCT0000024/3}. Appendix C of Technical Note 98 dealt with the combustibility of materials and paragraph 12.7 of Approved Document B. It stated:

"Clause 12.7 specifically refers to insulation materials and filler materials but is now being interpreted more generally (see BCA Guidance note 18). Therefore, where a building has a storey 18m or more above ground level all significant materials should be of limited combustibility (Class A2 in accordance with EN 13501). This includes but is not limited toː Rainscreen panels • Standard ACM panels do not meet these requirements. Limited combustibility ACM panels are available. Insulation materials • The only commonly used insulation material that will satisfy the definition of limited combustibility is mineral wool. …"⁷⁷⁷⁷ {CWCT0000024/13}.

Booth Muirie Technical Guidance Note 1

¶49.20 Booth Muirie Ltd is a company which provides specialist architectural cladding services, including design, manufacturing and distribution. In March 2016 it published a guide to designing multi-layered walls using ACM rainscreen panels.⁷⁸⁷⁸ {ARC00000559}. Like the BCA Technical Guidance Notes it set out various options for complying with the fire safety requirements for external walls of buildings over 18 metres in height. Option 1, which was described as "the most straightforward" was to restrict all the significant elements of each layer to non-combustible materials or materials of limited combustibility. Options 2, 3 and 4 were the same as those contained in Issue 1 of the BCA's TGN 18. Reynobond ACM with a polyethylene core, Celotex RS5000 and Kingspan K15 were all identified as being neither non-combustible nor of limited combustibility.