4 CONTEXT 177 : SEPTEMBER 2023 Risks of fast adoption From John Fidler, Marina Del Rey, California I was interested to read John Preston’s rendition of the decisionmaking and impacts of the scheme to clad the lead roofs of Kings College Chapel with photovoltaic cells (‘A world-wide precedent for solar panels?’ Context 176, June 2023). I greatly admire and appreciate John’s dedication and tenacity in the cause of appropriate energy conservation for historic buildings. This case must feel very depressing and issues a challenge to all of us similarly concerned. A few points and queries that follow on from his explanation of the case: 1. The subjectivity in the phrase ‘less than substantial harm’ surely needs to be addressed more aggressively by Historic England and its legal advisers through illustrated guidance and robust argument. This is otherwise a very large loophole for local planning committees to wriggle through to get what their politicians want. It seems that every planning and listed building consent application I have seen recently admits to the concept of harm, but dodges the bullet on substantive or degree of harm. Where is the detailed published weaponry for conservation officers on balancing heritage harm versus other socio-economic benefits? 2. What carbon offset was offered by the applicants with respect to the PV panels themselves? Many forms of PV panel are made via a dipping process, the chemicals from which are ozone-damaging. 3. What will be the physiochemical impacts of the PV arrays standing on top of the leadwork? The arrays will place the lead sheets under them in the shade, out of the sun, and the lead will therefore be colder than previously at night and over winter periods. Rainwater running over the surface will keep sheets wetter for longer without the otherwise hot daytime surface temperature drying them off quickly. What impacts will these circumstances have on new lead patination/corrosion, and condensate issues so far as thermal pumping and underside lead corrosion are concerned? Is anyone investigating these issues? Fast adoption of new technologies can have unforeseen risks. John Fidler Look out for faulty concrete From Charles Shapcott, conservation accredited engineer The civil and structural engineering watchdog CROSS (Collaborative Reporting for Safer Structures) UK has highlighted concerns with precast concrete floors and roofs made of reinforced autoclaved aerated concrete (RAAC). The material was marketed as being good at insulating roofs and floors, being a foamed concrete similar to early Thermalite walling blocks. A paper describes the difficulties experienced in service with RAAC roof planks on structures designed and built from the 1960s and finished before 1980. The units are about 600 mm wide and were dry jointed with smooth soffits, before the application of any surface finishes, sometimes painted direct. The trade Letters names of two manufacturers are Siporex and Durox. The defects prior to a major failure comprise excessive deflections and cracking, also identified in a number of roof planks, and there is evidence of the start of reinforcement corrosion. A roof with minimal falls may experience ponding in the middle of the span, increasing the loading above acceptable levels. Any water that gets into the material, through leaks, will be held there, unable to dry out, corroding the reinforcement. Certain chemicals that were used in the hydration and foaming of the concrete can be enlivened by unintended water being in the final matrix as built. Inspecting architects and others should look out for this type of construction during their quinquennial inspections. There have been more than 900 failures of RAAC planks in schools, hospitals and municipal buildings within the last few years, and this material may well have been used elsewhere. Charles Shapcott Since Context received Charles Shapcott’s letter, the risks of RAAC failure have been prominent in the national media. Proper governance From Richard Griffith RIBA RIAS Local authorities issue over 30,000 listed building consents each year. Those consents directly affect something like £2 billion worth of development. Yet the performance and effectiveness of listed building control are not measured at all. The control lacks even a single measured protection standard. There is no official explanation why listed building protection is not subject to measured regulation. There is no significant reason for its absence, and there are very significant reasons for its introduction. A straightforward framework of measured guardrails could be introduced without difficulty and without incurring any additional burdens at all for local authorities. Isn’t the introduction of proper governance long overdue? Richard Griffith
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