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

3. Methodology

18. To meet the aims and objectives outlined above, Building Warrant applications were reviewed with regards external wall systems to identify the assessment approach in the current process. The brief was to review eight Building Warrant applications from six local authority verifiers where the guidance in the technical handbooks recommended non-combustible external wall systems or the system has been tested in accordance with BS/ 8414 and met the performance criteria in BR/ 135. As the Building Regulations guidance changed on 1 October 2019, the intention was to review four building warrant applications with a top storey height over 18m between 1 May 2005 and 30 September 2019, and four building warrant applications with a top storey height over 11m from 1 October 2019 onwards. Six local authorities were initially approached as per the brief, three local authorities responded with suitable case study candidates. The actual number of case studies reviewed was reduced to three building warrant applications with a top storey height over 18m between 1 May 2005 and 30 September 2019, and two building warrant applications with a top storey height over 11m from 1 October 2019 onwards. It transpired during the course of reviewing one of the post-October 2019 case studies that the building top storey height is actually 9m.

19. Since 1 May 2005 the basis of compliance would expect to have been via the use of non-combustible materials, or systems compliant with BS/8414 / BR/135 or a fire engineered solution for over 18 m domestic buildings. Since 1 October 2019 this would extend to any building over 11 m. Any other route other than via non-combustible materials or BS/8414 / BR/135 would need to be fully justified.

20. The authors used their external wall systems experience to create a Guidance Tool (see Section 4) that was applied to the five case studies reviewed as part of this research to identify where there were gaps in the Guidance Tool for each case study. The outcomes of this were analysed to provide recommendations to Scottish Government/BSD/.

21. 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.

22. Interviews were held with the local authority case officers for these five building warrant applications. The intention was to understand how the local authority verifier arrived at the decisions taken specific to that case study in their own words. To obtain a broad range of responses, the same questions were put to all of the case officers for the case studies undertaken. The questions were derived from common themes in multiple case studies and/or to describe any processes that are routinely undertaken but perhaps not recorded, specifically relating to scrutinising the design of the external wall systems at both the design and construction stages. The findings of the interviews were analysed to provide recommendations to Scottish Government/BSD/. In order to inform the research and encourage open feedback, the project address and local authority have been anonymised. Data Protection legislation and copyright will be adhered to at all times.