Building standards - managing fire risks associated with use of external wall systems: research

7. Discussion

185. The reviews of the Case Studies were intended to gain a better understanding of the existing verification process to inform any potential solutions to provide appropriate, effective, and robust verification and compliance processes with regards to the design and construction of external wall systems. The observations in Section 5 therefore focus on identifying potential gaps in the verification processes applied to the Case Studies to improve future verification and compliance processes.

186. It is clear from the interviews that local authority verifiers in all case studies engaged in dialogue with Building Warrant applicants regarding external wall systems. There is evidence of this within the material provided for this research, but this was limited in quantity.

187. Differences were observed between the fire testing provided for the external wall systems components and/or materials in Case Studies 1 and 2, and there is no record of the local verifiers having contacted the manufacturer or testing house to confirm the validity of the proposed replacement products. During the interviews for all case studies it was noted that often decisions are made by experienced local authority verifiers where it is clear to them that minor changes will not impact the intended fire performance. Whilst this may be appropriate, it is the authors’ opinion that it would have been useful for a record to have been kept on file to allow the local authority verifiers to consider any future building changes against the basis of the original Building Warrant approval. Interviewees advised that if they contact manufacturers or testing houses for comments this will be saved to the project file, but this is not standard practice for decisions reached internally. The proposed Guidance Tool would assist here by identifying the differences in materials used and establishing the fire performance.

188. Data sheets that contain fire performance classification in accordance with the relevant British or European Standards were not available for all products in Case Studies 1, 2, 3, 4, and 5. During the interviews, it was noted for all five Case Studies that data sheets are not routinely requested where the local authority verifier has knowledge of the proposed products. Whilst this is valid, it is the authors’ opinion that since products are constantly evolving it would be prudent to keep a record of data sheets for the proposed materials, particularly as external wall cladding fire performance is specific to the materials used and therefore sensitive to any changes. During the interviews, local authority verifiers in all Case Studies noted that the list in the Guidance Tool would make clear to applicants what is expected of them, which should assist in avoiding instances of data sheets not being provided in the future.

189. Fire barrier products are specific to the materials and cavities they are installed in. Fire barriers and external wall types detail drawings were not provided for Case Studies 2, 3, and 4. It is the authors’ expectation that these details would have been provided to the local authority verifier as part of the Building Warrant application process for their review, but have not been made available to the authors for this research.

190. Fire barriers were shown with a lower fire resistance period than the internal walls that they are installed in line with in Case Study 2. The decision to approve these fire barriers is not recorded in the literature provided to the authors to review for this research, and such decisions should be recorded so that any fire safety features that the arrangement relies on are clearly understood. For example, the authors note that the internal wall construction achieves 60 minutes fire resistance from the inside; it is possible that this was a factor in the local authority verifier’s decision to approve this arrangement and this would have been useful to have been recorded and communicated with the design team so that building owners are aware of this prior to making future decisions of building changes.

191. In Case Study 4, the fire barrier product data sheet provided noted that they are applicable to timber frame or masonry/concrete construction types, which doesn’t reflect the building construction materials. The decision to approve these fire barriers is not recorded in the literature provided to the authors to review for this research, and such decisions would have been useful to have been recorded so that any fire safety features that the arrangement relies on are clearly understood.

192. In Case Study 4, a rigid insulation board is present as part of the external wall systems, and timber decking is noted on the external terraces of Case Study 4. The decision to approve these is not recorded in the literature provided to the authors to review for this research. Such decisions would have been useful to have been recorded so that any fire safety features that the arrangement relies on are clearly understood.

193. Fire barriers were not shown on the elevation drawings around services, doors, and window penetrations through the external wall systems for Case Studies 2, 3, and 4, and at the edges of the SFS/ systems at windows/doors for Case Study 4. The Case Study 5 elevation drawings do not show any fire/cavity barriers. There is no evidence in the literature provided for review that drawings showing barriers in the warrant plans were requested by the local authority verifiers, but the authors infer from the interview responses that this would have been captured on site by the local authority verifier team. However, it is the authors’ opinion that this should have been captured at the Building Warrant stage to ensure that the site agent allowed for cavity barriers in their costing and ordering.

194. A fire barrier was missed on the elevation drawing between two flats in Case Study 4. There is no evidence in the literature provided for review that this was captured by the local authority verifiers, but based on the responses in the interviews, the authors infer that this would have been captured on site by the local authority verifier. However, it is the authors’ opinion that this should have been captured at the Building Warrant stage.

195. In Case Study 5, the cladding materials included untreated timber cladding on treated softwood framing. The outline specification provided by the project architect referred to the BRE/ Fire Note 9 (BRE/ 1999). It is not clear how the local authority decided that this arrangement met the BRE/ fire note, and the decision to approve this is not recorded in the literature provided to the authors to review for this research. The authors infer from the interview that the local authority verifier used their experience of similar arrangements, but the specifics of the decision would have been useful to have been recorded so that any fire safety features that the arrangement relies on are clearly understood.

196. In the literature review, there was little information on the site inspections carried out by the local authority verifiers for Case Studies 1, 2, 3, 4, and 5 regarding external wall systems. At first glance this may seem as though limited inspections have been carried out by the local authority verifier, but the interviewees advised that in reality the local authority verifier are regularly on site for an extended period during the construction process. Therefore, the limited information is due to the fluid nature of construction sites requiring immediate resolution of issues. During the interviews, local authority verifiers advised that issues they observed on site are communicated verbally with the expectation that the site agent will resolve the issues prior to the next site visit by the local authority verifier. This is sometimes accompanied by photos as evidence of issues being resolved if they are closed up prior to the next site inspection, although this was not provided for review for this research. The interviewees also advised that there is no specific site visits exclusively for external wall systems, and that indeed all site visits are intended to be a general walk-around to raise any issues identified on the day. This aligns with the responsibility for construction quality sitting with the site agent, who should as a matter of good practice be recording completed installations (including photos) to prove compliance where required. However, the authors’ experience is that construction quality is frequently below the level expected, particularly regarding cavity/fire barrier installations even when photographic records are provided by site agents; the issues may be visible in the photographic records (e.g. gaps around closed-state barriers) or may only be apparent during the site inspection (e.g. missing brackets which would not be observed via photos only). Therefore, the authors’ view is that a more robust site inspection process is needed, which is presented in the Guidance Tool. Based on the feedback in the interviews, asking local authority verifiers to carry out this function would result in a significant uplift in their workload and would not be consistent with their responsibilities. It is therefore most appropriate for the responsibility for site inspections to lie with a suitably qualified third party acting on behalf of the site agent. In order to align with the current Building Warrant process, the third party inspector would need to prepare a site inspection report to present to the local authority verifier for their approval and records. This may assist in identifying specific items that the local authority verifier may wish to check on site as part of a spot-check approach under “reasonable inquiries”.

197. It is the authors’ view that applying the Guidance Tool would have addressed most of the items discussed above. From the interviews conducted, the local authority verifiers for all Case Studies were supportive of the Guidance Tool, on the basis that it would serve to both improve the quality of Building Warrant submissions pertaining to external wall systems and be a useful aide memoir to local authority verifiers. It was also identified that there may be improved consistency in terms of information requested by local authority verifiers on a project to project basis and throughout Scotland.

198. In the interviews, local authority verifier case officers for Case Studies 2 and 3 requested a tick-box style form to accompany the Guidance Tool to expedite the process of checking through the information for each wall type. As that is outside the scope of this research project, this should be reviewed as part of a separate exercise by the BSD/.

199. In the interview with the local authority verifier in Case Studies 2, 4, and 5 the initial impression of the Guidance Tool is that it seems complex, however it was recognised that the Guidance Tool formalises the process that case officers must carry out intrinsically. On this basis, the Guidance Tool will serve as an aide memoir to limit the potential for items being overlooked or missed. It is anticipated that with time and usage the Guidance Tool will be fully understood.

200. For the items that would have been addressed by more thorough recording of the decision making process by the local authority verifiers; there is no specific process suggested here. Each local authority will have their own range of experience and internal processes. The recently published guidance in PAS/ 9980 was reviewed for insight into a risk-based approach, however as PAS/ 9980 is not aligned with Building Regulations benchmarks its use in Scotland would be limited to potentially using its principles as part of the technical justification to support any non-standard external wall designs. However, this would need to be approved by the local authority verifier and would be subject to the verifier being comfortable with using PAS/ 9980 as a method of justifying departures from the Technical Handbook’s recommendations.

201. The interviewees felt that the local authority verifier case officers within their department are suitably skilled to carry out site inspections of external wall systems. However, most would be willing to rely on an appropriately accredited third party for the majority of the site inspection work for external wall systems. The local authority verifier case officer would still carry out at least one site visit as a spot-check for their own piece of mind. A means of establishing an accreditation scheme for this will need to be reviewed as part of a separate research project.