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Part B or Approved Part B?

Part B or Approved Part B?

That is the question.

Ambiguities in the statutory fire safety Building Regulations Part B and the practical guidance of Approved Document B. 

Authors: Ben Chamberlain, Diales Technical Expert, and Robert Foster, Diales Associate Director.

The fire safety requirements of the Building Regulations are under ever-closer scrutiny, as construction disputes relating to the flammability of external wall cladding and insulation, on high-rise residential buildings, continue to arise following the Grenfell Tower fire in 2017. But should designers bear liability where such products were specified and installed? In England and Wales, the Building Regulations are approved by the Secretary of State pursuant to the Building Act 1984. Within the Building Regulations 2010, the fire safety requirements were described at Schedule 1, Part B. Of particular relevance to insulation in external walls was section B3.(4), which required that: “The building shall be designed and constructed so that unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited.” Additionally, section B4.(1) related to external fire spread and required that: “The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the use and position of the building.” Both statutory requirements had remained unchanged since 1985.

The government also issues practical guidance about how building design and construction may meet the statutory requirements by way of a series of Approved Documents. This guidance is updated periodically. At the time of the Grenfell Tower refurbishment, the relevant fire safety publication for high-rise residential developments was ‘Approved Document B, Volume 2 – Buildings other than dwelling houses, 2006 edition incorporating 2007 and 2010 amendments’ (‘ADB’). Although amendments were made to ADB in 2013, the guidance relevant to insulation and cladding, at sections 12.5 – 12.9, remained unaltered. Changes were also made to ADB in 2018, 2019, and 2020. However, current claims pertaining to external wall insulation and cladding tend to relate to projects begun under ADB 2010 (or earlier revisions). As such, that is our focus here. Arguably, there were ambiguities in sections 12.5 – 12.9 of ADB, which we shall examine below. There is also a question mark regarding the extent that designers can rely on the Approved Documents to discharge the statutory obligations of Schedule 1, Part B, given that the recently produced (July 2020) ‘Manual to the Building Regulations, A code of practice for use in England’, states:

“...simply following the guidance does not guarantee that your building work will comply with the legal requirements of the Building Regulations.” 

So, whilst the requirement at section 12.7 of ADB that: “In a building with a storey 18m or more above ground level any insulation product … used in the external wall construction should be of limited combustibility …”, is unequivocal, the arguments around cladding specifications are more nuanced, however. Since the Grenfell fire, much of the ensuing debate has understandably centred around Aluminium Composite Material (‘ACM’) cladding systems.

In hindsight, it is tragically apparent that non-fire rated ACM cladding panels did not meet the requirements of section B4.(1) of the Building Regulations. Despite the product’s evident failure to meet this statutory minimum, Paul Hyett, an architect, and former president of the Royal Institute of British Architects (‘RIBA’), does not believe that the designer’s specification of the ACM cladding, of itself, was unreasonable. In expert evidence to the Grenfell Inquiry, Mr Hyett argued that the cladding system that was installed was subject to a test certificate from the renowned British Board of Agrément (‘BBA’) affirming that: “… the [ACM] panels maybe regarded as having a Class 0 surface ...”.

Independently verified certificates published by the BBA are intended to give specifiers peace of mind that products are fit-for-purpose, safe, and comply with regulations and best practice guidelines. ‘Class 0’ is the external wall surface classification for the spread of flame, which is a prerequisite for materials used on residential buildings 18m or higher, (or closer than 1m from the boundary) under section 12.6 and Diagram 40 (see Figure 1) of ADB.

 Mr Hyett’s argument rests on the basis that the architectural profession should be able to rely on manufacturers’ published data and, particularly, BBA Certificates. Without confidence in such technical information, the profession would be ‘fumbling in the dark’ and, if the elements of each and every project had to be independently tested and certified, the construction industry would effectively grind to a halt.

Mr Hyett attested to the Inquiry that, although more detailed information of the cladding’s behaviour in relation to fire was contained at section 6 of the BBA Certificate, the designer’s acceptance of the ‘Class 0’ designation at face value was reasonable. However, section 6 of the BBA Certificate was less clear-cut. It stated that the ‘Class 0’ classification only applied to specific colours, and that alternative hues would require testing in line with ADB. Further, section 6.5 stated that: “For resistance to fire, the performance of a wall incorporating the product, can only be determined by test from a suitably accredited laboratory, and is not covered by this Certificate.” Also, can a designer simply accept a satisfactory surface spread of flame test result, which points to compliance with ADB section 12.6, without regard to ADB sections 12.5, 12.7 and the overarching requirement to comply with the Building Regulation B4.(1). Surely not!

External wall cladding is a significant cost and design element of both new build and refurbishment projects. Additionally, commonly used RIBA appointment contracts usually include the requirements for architects to exercise reasonable skill, care, and diligence in the discharge of their services.

Whilst the ‘Architects Code: Standards of Conduct and Practice’, published by the Architects Registration Board, enshrines “competence” as an expectation of the profession. As such, it is arguable that a competent designer, exercising reasonable skill, care, and diligence, should take more than a cursory glance at key technical data. So, should inconsistencies in BBA Certificates, such as those highlighted in the previous paragraph, prompt further technical probing of products and materials with manufacturers?

This point aside, there has also been considerable examination of the flammable polyethylene core sandwiched between the two sheets of 0.5mm thick aluminium that make up ACM cladding panels. The ‘Class 0’ rating, stated in the aforementioned BBA Certificate, only applied to the aluminium face of the composite panel and not to the plastic core. So, was it necessary to interrogate the complete makeup of the product prior to specifying it?

In Mr Hyett’s opinion, it was reasonable for designers to assume that the ‘Class 0’ classification of the Reynobond ACM applied to the product as a whole, including the core. Therefore, it was reasonable for designers to specify such products on high-rise buildings; notwithstanding any shortcomings in the technical data, where responsibility rested with manufacturers and/or certifying bodies.

However, section 12.5 of ADB also advises that: “The use of combustible materials in the cladding system … may present such a risk [for fire spread] in tall buildings.” This appears to refer to the system as a whole, suggesting that designers needed to take a holistic review of cladding systems, which, it could be argued, would include the make-up of composite materials, in order to discharge statutory obligations under the Building Regulations.

There has also been much debate regarding the nomenclature of the ACM polyethylene core and whether it falls within the definition of “filler material” under section 12.7 of ADB: “Insulation Materials/Products”, which requires the materials used to be of limited combustibility. In the immediate aftermath of the Grenfell fire, the government was quick to clarify its own position on this matter and wrote to local authority and housing association chief executives declaring that: “For the avoidance of doubt; the core (filler) within an Aluminium Composite Material (ACM) is an “insulation material/product”, “insulation product”, and/or “filler material” as referred to in Paragraph 12.7 …”.

Dr. Barbara Lane, a fire engineering expert, disputes this definition, however. In her own evidence to the Grenfell Inquiry, Dr. Lane asserted that: “… an ACP [ACM] rainscreen cladding layer is not an insulation material or product ….

It could be said that this point of view supported by British Standard 8298-4’s recommendation that rainscreen cladding, separated by an air gap, should be disregarded from thermal heat loss calculations. But is this an adequate differentiation, as to whether or not the core is helping prevent heat loss, it is often formed using a combustible insulation material?

Although the term “filler” is used commonly in the construction industry, Dr Lane also asserted that the polyethylene core of ACM panels was never termed thus, prior to the Grenfell fire. Her view was supported by Mr Hyett. In this context, his reading of “filler material” was that it “… relates to a product or material such as mineral wool, or PIR insulation – that is something consisting of the same material …throughout its make up.” Following this logic, there would have been no requirement for the ACM core to meet the limited combustibility requirements of 12.7 of ADB; but should the general warning at section 12.5 regarding: “…combustible materials in the cladding system…” have been heeded? Or was it sufficient to ensure that the cladding surface had ‘Class 0’ designation, as required by section 12.6?

The historic use of products such as ACM cladding in high-rise buildings is often attributed to these alleged ambiguities within ADB; confusion over ADB’s practical guidance status against the statutory requirements of Schedule 1, Part B of the Building Regulations, as well as certification that blurred the distinction between compliance with sections 12.6 and 12.7 of ADB, which left designers operating within a somewhat grey, and sometimes confusing, framework. Whilst the question of whether compliance with ADB itself is sufficient to comply with Schedule 1, Part B of the Building Regulations remains open for debate.

Had the Grenfell fire not occurred, and its immediate lessons been learnt, it is quite probable that non-fire rated ACM cladding would still be used on high-rise residential buildings today. However, since the fire, the practical guidance within ADB has been updated and clarified, and now precludes the use of combustible materials in the construction of external walls for high-rise residential buildings.

Originally written as part of the Driver Trett Digest, issue 24. To view the publication, please visit: www.driver-group.com/digest-compendium


Articles  /  Digest  /  Europe  /  Global

Articles  /  Digest  /  Europe  /  Global

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