Chapter 27: Siderise cavity barriers

Chapter 27: Siderise cavity barriers

Background

¶27.1 Siderise Insulation Limited ('Siderise') designs and manufactures fire, thermal and acoustic insulation products for use in curtain walling and cladding. It also supplies associated products, such as brackets, sealants and tapes for use with its products.^19571957 Swales {SIL00000306/3} page 3, paragraphs 11 and 13. It sells direct to customers or through distributors.^19581958 Swales {SIL00000306/3} page 3, paragraph 11. It is a member of various industry bodies, including the Centre for Window and Cladding Technology and the Association for Specialist Fire Protection.^19591959 Swales {SIL00000306/4} page 4, paragraph 14. It has contributed to the development of publications and guidance relating to external walls^19601960 Including the ASFP Red Book chapter "Firestopping: Linear Joint seals, penetrations & cavity barriers", Swales {SIL00000306/4} page 4, paragraph 14. and has hosted industry conferences on facades in collaboration with the Building Research Establishment (BRE).^19611961 Swales {SIL00000306/4-5} pages 4-5, paragraph 16. The first was on 1 November 2012 and the second on 13 January 2016.

¶27.2 As well as manufacturing cavity barriers, Siderise provided additional services to its customers,^19621962 Siderise Site Services dated January 2016 {SIL00002589}. including advice on the suitability of its products for particular applications^19631963 Swales {SIL00000306/7} page 7, paragraph 28. and guidance on installation.^19641964 Siderise Site Services dated January 2016 {SIL00002589}.

Product Development and Testing

¶27.3 A cavity barrier is defined in Appendix E of Approved Document B as "a construction, other than a smoke curtain, provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space."^19651965 Approved Document B 2013 {CLG00000224/143}. The guidance in Approved Document B is that cavity barriers should provide 30 minutes' integrity and 15 minutes' insulation when tested to the relevant part of BS 476.^19661966 Approved Document B 2013 {CLG00000224/125} Table A1, Item 15.

¶27.4 According to Siderise's witnesses, cavity barriers were traditionally tested in accordance with the general principles set out in BS 476 Part 20,^19671967 Mort {SIL00000298/10} page 10, paragraph 38; {BSI00001748}. which is the British Standard containing general principles governing the method of determining the fire resistance of elements of construction.^19681968 {BSI00001748/1}. Part 20 was accompanied by supplementary standards for testing specific elements of construction, namely, Part 21 for loadbearing elements, Part 22 for non-loadbearing elements, Part 23 for fire-protecting suspended ceilings and Part 24 for ventilation ducts.^19691969 Part 21 {BSI00001745}; Part 22 {BSI00001743}; Part 23 {BSI00000074}; Part 24 {BSI00000075}. Those supplemental parts did not apply to cavity barriers, which had to be tested in accordance with the general fire resistance principles outlined in BS 476-20.^19701970 Mort {Day102/16:23}-{Day102/18:1}.

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¶27.5 The cavity barriers installed at Grenfell Tower were vertical "full-fill" barriers and horizontal "open-state" barriers. A full-fill barrier consisted of a solid piece of material spanning the entire cavity, thus forming a permanent vertical barrier against the horizontal spread of fire. An open-state barrier had a gap between the face of the barrier and the rainscreen panels to allow the passage of air and moisture. It had an intumescent strip on the outside edge that was designed to expand to fill the gap when exposed to heat in order to restrict the passage of fire vertically.^19711971 Mort {Day102/21:3-16}. The intumescent strip could be effective in sealing the cavity only if the surface against which it expanded remained in place.^19721972 Mort {Day102/22:13-24}. The effectiveness of a "full-fill" cavity barrier also depended on the integrity of the surfaces it abutted, in particular the rainscreen.

¶27.6 Stephen Swales, Chief Commercial Officer at Siderise, explained that from the late 1990s onwards Siderise had begun to develop open-state cavity barriers in response to demands from industry for a product that would leave a gap to allow for ventilation and the passage of moisture behind the rainscreen but which would close the gap in the event of fire.^19731973 Swales {SIL00000306/11-12} pages 11-12, paragraphs 44-46. From around 2002 Siderise began to evaluate a number of different intumescent materials through a programme of testing carried out with the company that later became Exova.^19741974 Swales {SIL00000306/12} page 12, paragraph 45.

¶27.7 Christopher Mort, the Sales and Technical Engineer for Siderise (and from 2011 their Technical Officer for Fire), was responsible for ensuring that the new product complied with the relevant statutory and regulatory requirements.^19751975 {SIL00002586}, {SIL00002587} and Mort {Day102/27:4-13}. At a product development meeting in July 2006 it was agreed that the aim was for the product to meet the requirements of a modified BS 476 Part 20 test.^19761976 {SIL00002587}. Mr Mort told us that it had been accepted within Siderise that testing to the general principles of BS 476 Part 20 was not ideal, as the standard could not be applied directly to open-state cavity barriers.^19771977 Mort {SIL00000298/10} page 10, paragraph 38. (There was no precedent for testing open-state cavity barriers and Siderise was the only company embarking on such testing at the time.)^19781978 Swales {SIL00000306/10} page 10, paragraph 39 and Mort {Day102/43:23}-{Day102/44:8}. The standard test procedure in BS 476 Part 20 was therefore modified following discussions with Exova, in particular to dispense with the requirement that there be no gaps present at the start of the test.^19791979 Mort {Day102/28:24}-{Day102/29:7}. The standard test procedure involved pushing a metal rod into the test specimen. If it was possible to penetrate the full width, the product failed the test.^19801980 Mort {Day102/29:8-13}. All open-state cavity barriers automatically failed that requirement because of the gap that was present in the cold state. Instead, Siderise agreed with Exova that it would monitor and record the closure of the gap and test the integrity of the product at that stage.^19811981 Mort {Day102/29:18}-{Day102/30:12}.

¶27.8 At no stage did Siderise or Exova ask any other industry bodies or anyone in government whether such a test method was appropriate. Siderise relied entirely on the advice it received from Exova.^19821982 Mort {Day102/44:24}-{Day102/45:13}.

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¶27.9 Between 2007 and 2011 Exova carried out four tests on open-state cavity barriers on which it produced reports.^19831983 February 2007 {SIL00000290}; January 2009 {SIL00000223}; August 2010 {SIL00000224}; September 2011 {SIL00000211}. During each of the tests the product was held between two concrete lintels.^19841984 Mort {Day102/63:7-10}; {Day102/65:14-18}; {SIL00000290/12}; {SIL00000223/4}; {SIL00000224/12}; {SIL00000211/5}. Insulation and integrity were measured only after the intumescent strip had closed the gap.^19851985 Mort {Day102/63:21}-{Day102/64:4}; {SIL00000290/28}; {SIL00000223/3}; {SIL00000224/23}; {SIL00000211/8}. All the reports contained important qualifications about the procedure that had been adopted. They stated that the results related only to the behaviour of the specimens under the particular conditions of the test, were not intended to be the sole criteria for assessing the potential performance of the products in use and did not reflect their behaviour in an actual fire. In addition, they stated that the results of the tests might not be applicable to situations in which the width of joints, orientation or supporting construction varied from those of the test. Since no movement was induced during the tests it was not possible to evaluate the products' performance where movement was induced under actual fire conditions.^19861986 {SIL00000290/28}; {SIL00000223/7}; {SIL00000224/24}; {SIL00000211/7}. They were important qualifications, because they set out clear limits on the testing that Exova had undertaken.^19871987 Mort {Day102/68:17-21} and {Day102/69:2-4}. Anyone reading the test reports should have appreciated that they could not be relied on to predict with any accuracy how the products would perform in a fire or, in particular, how they would perform as part of a ventilated rainscreen system. That was made particularly clear in the test report issued in 2011, which included the following paragraph drawing attention to the risk of failure of the rainscreen:

"This report does not consider the fire resistance performance of the rainscreen element or whether fire spread may occur as a consequence of collapse or failure of the rainscreen. The approving authority or regulator should decide whether it is necessary for the rainscreen to be 'fire rated', whether it is of an appropriate construction and whether separate test or assessment evidence is necessary."^19881988 {SIL00000211/4}.

¶27.10 In the test report dated 20 September 2011^19891989 {SIL00000211/7}. Exova combined favourable integrity test results from tests carried out in 2010^19901990 {SIL00000224/3}. with favourable insulation results from tests carried out in 2007^19911991 {SIL00000290/4}. and concluded that Siderise open-state cavity barriers would achieve 60 minutes' integrity and 30 minutes' insulation respectively,^19921992 Mort {Day102/77:25}-{Day102/78:12}. although no one specimen had produced both results.^19931993 Mort {Day102/78:13-16}. Nonetheless, there is no reason to think that the product did not in fact meet those standards.

¶27.11 Siderise considered that successful testing to some, but not all, of the requirements of BS 476 Part 20 would evidence compliance with the guidance in Approved Document B, as it would demonstrate that the open-state cavity barriers met the requirement for 30 minutes' insulation and 15 minutes' integrity.^19941994 Mort {Day102/32:2-7}.

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Testing in accordance with BS 8414

¶27.12 According to Mr Swales, before the Grenfell Tower fire there had been a general reluctance to conduct large-scale tests in accordance with BS 8414 as they were considered too costly.^19951995 Swales {SIL00000306/17} page 17, paragraph 64. However some guidance relating to the use of cavity barriers suggested that it was nevertheless important to consider whether full-scale testing for reaction to fire (as opposed to resistance to fire) might provide important information on whether they could perform effectively as part of a ventilated rainscreen system. For example, Technical Report 31 of the European Organisation for Technical Approvals on "Fire Resistance Tests for Cavity Barriers" dated October 2008^19961996 {INQ00014544}. stated that the method of testing it described was not applicable to horizontal cavity barriers in rainscreen cladding systems because it was difficult, if not impossible, to model the correct thermal exposure and boundary conditions in a test for resistance to fire. It therefore recommended that the fire resistance of horizontal cavity barriers be assessed in the context of a full-scale facade test.^19971997 {INQ00014544/7} section 1, paragraph 4. According to Mr Swales, Siderise was a strong advocate of BS 8414 testing and was keen to test its cavity barriers in that way, having actively sought out partners for such tests in the period before 2017.^19981998 Swales {SIL00000306/17} page 17, paragraph 64.

¶27.13 At the time Siderise cavity barriers were specified for use on Grenfell Tower, Mr Mort was not aware of any testing that had been undertaken by Siderise, or by anyone else using its products, that demonstrated how they would perform in conjunction with metal composite rainscreen panels.^19991999 Mort {Day102/122:10-22}. However, it had taken part in six BS 8414 tests between 2012 and May 2015.^20002000 Swales {SIL00000306/17} page 17, paragraph 63. The cladding used for those tests had been rainscreen boards or terracotta tiles but not aluminium composite material;^20012001 Mort {Day102/136:14-19}. the insulation had been either PIR or phenolic foam boards or mineral wool.^20022002 Swales {SIL00000306/17} page 17, paragraph 63. Not all of the systems tested met the criteria in BR 135. In particular, a test undertaken in conjunction with Celotex RS5000 insulation in February 2014 failed to do so.^20032003 {Day102/135:19}-{Day102/136:2}. For our factual findings in relation to these Celotex tests see Chapter 24. Mr Mort was aware that during the test the Marley Eternit panels had pulled away from the rig and distorted, thereby rendering the cavity barriers ineffective because they had nothing against which they could form a seal.^20042004 Mort {Day102/144:8-12}. Siderise was aware that the effectiveness of its cavity barriers, whether full-fill or open-state, in creating and maintaining a seal depended on the integrity of the rainscreen.^20052005 Mort {Day102/145:8-17}.

Industry Testing

¶27.14 Since it was not possible to test open-state cavity barriers in accordance with BS 476 Part 20,^20062006 Swales {SIL00000306/13} page 13, paragraph 49 and Mort {Day102/80:25}-{Day102/81:3}. Siderise worked with the Association for Specialist Fire Protection, laboratories, certification engineers, manufacturers,^20072007 Including Siderise, Hilti, Rockwool, Firetherm, Firestopit and Promat. members of the Comité Européen de Normalisation and the British Standards Institution to develop a new method of testing entitled "Technical Guidance Document 19" ("TG19").^20082008 Swales {SIL00000306/13} page 13, paragraph 49. The test, which was published by the Association in 2014, required an open-state cavity barrier to close within five minutes of the beginning of the test.^20092009 {SIL00001540/14}. Any failure of integrity before that was to be disregarded unless any part of the surface exhibited sustained flaming above the seal.^20102010 {SIL00001540/15}. In other words, the test standard permitted the response of the product during the first five minutes to be ignored, save in the event of extreme flaming.^20112011 Mort {Day102/123:17}-{Day102/124:1}.

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¶27.15 TG19 was specifically designed for small-scale furnace testing of open-state cavity barriers.^20122012 Mort {SIL00000298/11} page 11, paragraph 40. Small-scale furnace testing was considered appropriate because it demonstrated the performance of the product in isolation.^20132013 Mort {Day102/91:14-24}. The test did not, therefore, extend to assessing the performance of open-state cavity barriers as part of a ventilated rainscreen system.^20142014 Mort {Day102/101:9-21}. TG19 expressly recommended that to evaluate the performance of open-state cavity barriers as part of a cladding system, a large-scale test, such as a BS 8414 test, should be considered.^20152015 {SIL00001540/3}. It also referred to a warning in the second edition of BR 135 that small-scale tests had been found not to reflect the fire hazard associated with full‑scale cladding systems.^20162016 {SIL00001540/17}. Siderise appreciated the importance of that warning before it became involved in the Grenfell Tower refurbishment.^20172017 Mort {Day102/128:1-13}.

¶27.16 Technical Note 17 published by the Centre for Window and Cladding Technology in March 2011^20182018 {CWCT0000019}. also contained a warning that cavity barriers could be tested in accordance with the principles contained in BS 476-20 (and other similar standards), but that their performance in conjunction with rainscreen panels might be different.^20192019 {CWCT0000019/5}. Mr Mort confirmed that he had been aware of that guidance from 2011.^20202020 Mort {Day102/131:7}-{Day102/132:5}.

¶27.17 The recommendation that any proposed system be tested in accordance with BS 8414 was included in TG19 because the two tests served different purposes. The test described in TG19 measured the properties of a cavity barrier, in particular the duration of insulation and integrity, in isolation but, unlike a BS 8414 test, did not measure the performance of an external wall system as a whole.^20212021 Mort {Day102/117:19}-{Day102/118:4}. On the other hand, a BS 8414 test did not measure the performance of individual components.^20222022 {SIL00001540/16}; Mort {Day102/120:3-10}. Siderise was aware before the Grenfell Tower fire that if cavity barriers were used as part of a ventilated rainscreen system, the rainscreen panels might distort or become detached and thus compromise the effectiveness of the cavity barriers.^20232023 Mort {Day102/120:11}-{Day102/121:20}.

¶27.18 On 15 May 2013,^20242024 Swales {SIL00000306/13} page 13, paragraph 50 and {SIL00000212/3}. Siderise again tested open state cavity barriers on 24 April 2014 with Chiltern International {SIL00000288}. Siderise tested an open-state cavity barrier between two concrete lintels^20252025 {SIL00000212/2}; Mort {Day102/92:6-16}. in accordance with a draft version of TG19.^20262026 Entitled "ASFP TG 3 N64, fourth draft February 2013". Exova produced a report on 23 July 2013^20272027 {SIL00000212}. which contained warnings similar to those in the reports mentioned above. In particular, it made it clear that the test results were not to be used as the sole basis for assessing the fire performance of the cavity barriers and that the results were not applicable to situations in which the width of the joints or the depth, orientation or supporting construction was different. It also drew attention to the fact that the test did not induce movement and therefore might not represent conditions that would be encountered in a fire.^20282028 {SIL00000212/32}. The report also made it clear that the results were applicable only to a void of the size tested.^20292029 {SIL00000212/34}. Siderise staff understood those limitations, including the staff in its sales and marketing teams.^20302030 Mort {Day102/100:7-20}.

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¶27.19 As far as Mr Mort was aware, there were no discussions with DCLG about adding a reference to TG19 to Approved Document B.^20312031 Mort {Day102/134:16-23}.

Extended Application Assessments

¶27.20 Siderise also carried out extended application assessments for cavity barriers of the kind that were used at Grenfell Tower. For that purpose, it used data from previous tests to calculate whether the products could be used in situations other than those in which they had been tested.^20322032 Mort {Day102/174:10-16}. That enabled it to assess the ability of its open-state cavity barriers to seal voids of greater width than those that had been used for the tests.^20332033 Swales {SIL00000306/14} page 14, paragraph 52.

¶27.21 All the extended application assessments for the products as used on Grenfell Tower were signed by Christopher Mort and dated 23 June 2017;^20342034 {SIL00000204/22}; {SIL00000204/29}; {SIL00000204/35-6}; and {SIL00000204/42-43}. in other words, they post-dated the fire by a few days.^20352035 Mort {Day102/175:2-18}. No formal assessment had been carried out before that date, or at any rate no reference to one appeared in any document.^20362036 Mort {Day102/178:21}-{Day102/179:13}. Mr Mort said that informal assessments had been carried out, but he accepted that there was nothing in the documents provided to us to support that.^20372037 Mort {Day102/180:13}-{Day102/181:5}. At Grenfell Tower, Siderise supplied cavity barriers for voids of between 326 and 425mm without having tested its products in voids of that width and without having undertaken any formal extended application assessments.^20382038 Mort {Day102/180:13-21}.

¶27.22 Even when Siderise did undertake formal extended application assessments in June 2017, it did not seek any external verification for its conclusions.^20392039 Mort {Day102/177:8-16}. Mr Mort's explanation was that external validation was not required by Siderise or by Approved Document B.^20402040 Mort {Day102/177:20-23}. It did not occur to him that it might be inappropriate for Siderise to certify its own products for use in extended applications without the support of an independent expert.^20412041 Mort {Day102/178:4-8}.

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Marketing material

Datasheet 2110

¶27.23 In mid-2012 Siderise produced datasheet 2110 relating to Lamatherm cavity barriers for rainscreen cladding.^20422042 {SIL00004672}. It gave copies of it to Harley in August 2013 in connection with two projects which required rainscreen cavity fire barriers.^20432043 Richard Kay (Siderise) emailed it to Mark Harris (Harley) in relation to the Wayland House project on 19 August 2013 {SIL00000325/2}. Richard Kay also sent it to Tim Lovell (Harley) in relation to the 10 Trinity Square project on 5 August 2013 {SIL00000327}. The title of the datasheet was "Cavity Barriers for Rainscreen Cladding". In the introduction it stated that rainscreen cladding systems typically incorporated a ventilated air space to allow the drainage of rainwater and that, to accommodate that design feature, Siderise had developed a purpose-made solution, namely, a horizontal cavity barrier with an integral intumescent strip along the edge which "fully closes the ventilated air gap in the event of a fire".

¶27.24 The datasheet referred to the four Exova reports^20442044 As discussed above, February 2007 {SIL00000290}; January 2009 {SIL00000223}; August 2010 {SIL00000224}; September 2011 {SIL00000211}. and said that the product had been tested by Exova and in its opinion represented a practical solution for a particularly demanding condition.^20452045 {SIL00004672} section 'Introduction', second column final paragraph. However, nowhere in any of the reports had Exova expressed that opinion.^20462046 Mort {Day102/197:4-12}. Mr Mort told us that he had reviewed the data sheet to ensure that it was accurate,^20472047 Mort {Day102/193:4-6}. but he was unable to explain how it had included Exova's apparent endorsement.^20482048 Mort {Day102/199:11-16}. He suggested that there might have been conversations with Exova, of which he had been unaware at the time, during which Exova had expressed that opinion,^20492049 Mort {Day102/196:16-20}; {Day102/197:10-21}. but we think that unlikely, since as Sales and Technical Engineer, he had a leading role in arranging and attending the testing with Exova.^20502050 Mort {SIL00000298/2} page 2, paragraph 7(b); Mort {Day102/69:6-17}. Plainly, Siderise should not have relied in its marketing material on an endorsement that was not genuine.

¶27.25 Under the heading "Advantages", the datasheet set out the results achieved in tests conducted by Exova using the principles of BS 476-20 & BS EN 1366-4:2006.^20512051 {SIL00004672/1}. It stated that a technical failure of integrity and insulation was deemed to have occurred at the start of the test due to the passage of flame through the open void, but went on to state that following the rapid expansion of the intumescent strip, the gap had become fully sealed and that the product had achieved the required standards for integrity and insulation.^20522052 {SIL00004672/1} section "Fire Performance".

¶27.26 The datasheet did not describe the nature of the test in detail, nor did it reflect any of the qualifications set out in the test reports, including the warning that the results might not apply to situations in which the supporting construction differed from that of the test. The datasheet also failed to warn the reader that it was not possible to evaluate the product's performance in circumstances where movement of the supporting construction was induced by exposure to fire. Finally, the datasheet did not draw attention to the fact that cavity barriers might be rendered ineffective if the rainscreen became distorted or dislodged in a fire.

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¶27.27 If the construction industry is to function effectively and safely it requires products that do the job expected of them and are marketed honestly. Although there is no evidence to suggest that, unlike Arconic, Kingspan and Celotex, Siderise set out in its marketing literature deliberately to mislead, it was suggested that its datasheet was in fact misleading because it suggested that its cavity barriers were effective when used in rainscreen cladding systems of all kinds, when the tests it had carried out did not support that claim.^20532053 {BSR00000070/31} page 31, paragraph 9.1. We think that the datasheet should have described more fully the nature of the tests it had carried out. The unqualified statement that the horizontal cavity barrier "fully closes the ventilated air gap in the event of a fire" tended to suggest that it would do so regardless of the nature of the rainscreen panel against which it was to form a seal. On the face of it, that was misleading, because no test had been carried out in conjunction with any recognised form of rainscreen panel. However, it is unlikely that any competent designer reading the datasheet would have been misled about the suitability of the product for particular rainscreen applications.

¶27.28 The title of the datasheet, "Cavity Barriers for Rainscreen Cladding", indicated no more than that the product had been designed for use in rainscreen cladding systems, which was indeed the case. Any competent fire engineer should have been aware of the warning in the second edition of BR 135 that small-scale tests on individual products had been found not to reflect the fire hazard associated with full-scale cladding systems^20542054 {SIL00001540/17}. and would have realised that the effectiveness of cavity barriers in any ventilated rainscreen system depends not only on the quality of the product itself but on whether the rainscreen panels remain in place during a fire. A competent fire engineer would also have asked for the underlying fire test data^20552055 Siderise made those available only on request: Mort {Day102/73:8-24}. to obtain a proper understanding of the tests that had been carried out on the product.

¶27.29 We recognise, however, that this kind of marketing literature would also have been read and relied on by a wide range of construction professionals, including architects, cladding designers^20562056 Jonathan Sakula's evidence was that specialist cladding designers would normally have referred to the manufacturer's technical literature Sakula, Façade Expert Report {JOS00000001/49} paragraph 12.1. and building control officers, some of whom might not have been familiar with test method BS 476-20. Although Siderise argued that anyone familiar with BS 476 Part 20 or BS EN 1366-4 would have been aware that tests on cavity barriers are carried out on the product held between concrete lintels,^20572057 {SIL00010048/12}. its marketing literature stated only that the tests had been carried out "using the principles" of those methods.^20582058 {SIL00004672/1}. We do not think that some professionals, for example, reasonably competent cladding contractors, could be expected to be familiar with those fire resistance tests, although they should have appreciated that tests on cavity barriers are generally conducted with the product held between walls of fire resisting construction and that their performance in conjunction with rainscreen panels might be different.^20592059 Sakula {Day125/80:5}-{Day125/81:8}. However, anyone with even a basic understanding of the principles underlying the use of cavity barriers who gave the matter a moment's thought would have realised that, if the rainscreen became distorted or dislodged for whatever reason, no cavity barrier of any kind could continue to be effective.

¶27.30 Although the datasheet was intended to, and did, tell the reader that the intumescent strip would expand effectively to close the gap in a rainscreen system in the event of a fire, the description of the way in which it worked made it clear that the claim was based on an assumption that the rainscreen would retain its integrity and provide a stable surface against which the intumescent strip could expand. It may not have been clear to some readers of the datasheet that the product had been tested between two concrete lintels, but any competent designer should have appreciated that the stability of the rainscreen was essential to its effective operation, as it was to the effectiveness of the vertical full-fill cavity barriers.

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¶27.31 It has been suggested that Siderise ought to have postponed marketing its products for use in rainscreen applications until there was a body of data from BS 8414 tests which demonstrated that they were effective when used in conjunction with particular rainscreen panels, and then only for use in systems of those kinds. In our view that is unrealistic. The BS 8414 test is not designed to test individual products and the behaviour of the rainscreen in response to an actual fire may depend on many factors. It may not accurately reflect its behaviour in a test. The fact is that the cavity barriers sold by Siderise, both full-fill and open-state, met the claims made for them in relation to integrity and insulation and the open-state barriers functioned effectively when tested in accordance with the principles of BS 476-20. Design professionals must take responsibility for ensuring that the choice of rainscreen panel will not render the cavity barriers ineffective. No competent design professional could reasonably have understood the datasheet to mean that the cavity barrier would remain effective even if the rainscreen became seriously distorted or detached and no one claimed to have understood it in that way.

¶27.32 The statement that the ventilated air gap would be fully closed in the event of a fire was therefore subject to the implicit qualification that the rainscreen remained in place and retained its rigidity and integrity. That qualification would have been obvious to a competent designer or cladding contractor but not necessarily to others. Siderise could not assume that everyone who read the datasheet would be competent and would be aware of the implicit qualification. It should therefore have made the qualification explicit.

Sending the datasheet to Harley

¶27.33 When Siderise sent datasheet 2110 to Harley in August 2013 it did not provide Harley with any information about the suitability in general of cavity barriers for use in rainscreen systems or the potential limits on their effectiveness. Nor did it refer to the nature of the tests that it had carried out on its own product. However, it was for Harley and others to determine whether the combination of materials it was using on a particular project, including the external wall at Grenfell Tower, would satisfy the Building Regulations. Siderise was not asked for general advice about the suitability of its products for use at Grenfell Tower nor is there any evidence that Harley relied on datasheet 2110 for the purposes of the design of the external wall. Siderise cannot reasonably be criticised for failing to point out to Harley that if a rainscreen failed, the cavity barriers would cease to be effective.

Postscript

¶27.34 Functional requirement B3(4) of the Building Regulations requires a building to be designed and constructed so that the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited. Functional requirement B4(1) requires that the external wall shall adequately resist the spread of fire over the walls having regard to the height, use and position of the building. Section 9 of the 2013 revision of Approved Document B provided guidance on the use of cavity barriers. It included advice in paragraph 9.15.d^20602060 {CLG00000224/86}. that they should be fixed so that their performance is unlikely to be made ineffective by the failure in a fire of any material or construction which they abut. The risk that cavity barriers in the external wall construction of a building with ventilated rainscreen cladding might become ineffective if the rainscreen failed appears therefore to have been foreseen. Despite that, none of those involved in the design of the refurbishment of Grenfell Tower appears to have considered how the rainscreen was likely to react if exposed to fire or whether its behaviour might undermine the effectiveness of the cavity barriers. In our view, designers should give much more thought to the behaviour in fire of rainscreen panels intended for use in conjunction with cavity barriers in order to comply with functional requirements B3(4) and B4(1).

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