Dangerous concrete - what Cardiff Council knew and when
Cardiff council have just released papers which shed more light on what they knew and when about dangerous concrete in St David’s Hall.
Following a complaint by Cardiff Civic Society to the Information Commissioner’s Office, the council have released previously confidential papers about the building’s condition. The papers were presented to Cardiff council’s cabinet in December 2022 but kept secret from the public. To obtain this information, the Society followed advice from the excellent WhatDoTheyKnow.com service. You can read the redacted documents in full below.
The Information Commissioner rejected Cardiff council’s view that these documents should be kept secret. The Commissioner said:
“St David's Hall is a significant cultural asset and there is a strong and legitimate public interest in information regarding how it is being maintained by the Council. There is also a strong public interest in disclosure of information relating to the safety of the building.”
You can download the Commissioner’s full findings below.
On the dangerous concrete, known as RAAC, the papers contain the following information:
From Dec 2021 report: BUILDING CONDITION SURVEY (updated May 2022)
4.2.1.b. In light of the recent SCOSS Alert (see section 3.2.1 ) the condition and robustness of the RAAC roof planks should be established and a risk assessment undertaken. This may require:
a thorough visual inspection to identify cracking and evidence of corrosion of the reinforcement;
a level survey to establish whether plank deflections are within acceptable limits;
assessment using non-intrusive techniques, possibly verified by localised intrusive inspection, to establish the adequacy and robustness of the bearing offered to the planks and position and arrangement of reinforcement.
Access onto the roof should be controlled and limited as far as practicable until the condition and robustness is established.
The assessment may determine the need for strengthening or other remedial works, e.g. to enhance the robustness at the bearings. The design life of RAAC planks has likely been exceeded, and this should be borne in mind when considering implementation of the recommendations of the assessment.
c) The condition of the lead roof and other roof panels should be reviewed by a specialist to advise on suitable repairs and improvements to reduce the risk of water ingress and injury / damage to persons / property below.
ST DAVID'S HALL REFURBISHMENT - STAGE 1 BUDGET COST ESTIMATE (May 2022)
It was identified in May 2022 that there was need to replace the RAAC in St David’s Hall with composite steel lightweight concrete and a specialist design quotation was required. The work was coded red for essential.
St David’s Hall building management summary (Dec 2022)
Roof Planks
Description: St David’s Hall roof structure is constructed from a combination of steel roof trusses and Reinforced Autoclaved Aerated Concrete (RAAC) planks (923 planks in total). It is generally recognised that RAAC has a serviceable life span of 30 years (under normal conditions). Recent construction safety alerts have reinforced the safety issues relating to RAAC, highlighting circumstances where they have failed and caused the collapse of a roof and/or structure without warning. Therefore, since St David’s Hall was constructed between 1977 to 1982, the RAAC planks are a cause for concern, as they are outside their intended design life span.
Risks: It is highly likely that different batches of planks (with different ages) have been used in the construction of the roof with varying manufacture quality control (that is often poor) over their construction and the dispositions of the reinforcement relative to the short bearing lengths typically used which significantly increases the shear risk. Therefore, these issues along with the RAAC planks being outside their serviceable life span increases the risk of failure and collapse of the planks.
Management arrangements: Included in the property condition and engineers report from WSP (dated 9 December 2021) is a deflection survey of the RAAC planks to establish whether plank deflections are within acceptable limits. Due to obstructions and access constraints, data was captured, and deflections calculated for 618 of the 923 planks (67% of the total number of planks). No excessive deflections (exceeding span/200) were noted in the 618 planks where data had been captured. The report suggested that as the plank deflections captured were all less (better) than span/200, that the next deflection inspection be carried out in five years i.e. on or before 9th December 2026 (provided no deterioration in condition becomes apparent).
An internal visual inspection of the roof RAAC planks is carried out (by a competent structural engineer) after the roof has been exposed to severe weather conditions e.g. extremely high temperatures, extremely low temperatures, extreme winds, snow or where water ingress has been identified.
Maintenance staff regularly carry out inspection and unblocking of roof drainage/water outlets to ensure they are clear and allow free drainage of water from roof areas.
Regular inspection of all roof waterproof membranes to ensure they are maintained in good condition.
Regular inspections will continue to be undertaken by WSP (The Institution of Structural Engineers (IStructE) have created a list of professionally registered structural engineers who have experience of providing solutions for managing RAAC planks, which WSP are represented on) and following extreme weather events and recorded on the Council’s electronic database (RAMIS).
Urgency / Timescales: ASAP
WSP in their report propose (as a medium-term solution) that remedial works be undertaken to install steel supplementary purlins to overcome the risk of failure of the RAAC planks. However, this work would be hampered by acoustic and air conditioning ducting within the roof space that may be problematic. These works would require a significant amount of scaffolding to be erected to work from, and would require the venue to be closed for the period that the scaffolding were erected, and the works carried out (likely to take in excess of 9 months).
Based on costs calculated in December 2021 WSP estimated these works to cost in the region of [redacted] plus the associated services alteration costs.