87 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 MASONRY 3.2 MASONRY and CLIMATE CHANGE CAMILLA FINLAY ALL OF those working within the heritage sector are acutely aware of the increasing challenge we face maintaining our built heritage and ensuring it is passed on to the next generation in better condition and better understood than it was received. More recently though it has become clear that climate change is becoming a major factor in this challenge. The UK declared a climate emergency in 2019. Historic England describes climate change as a ‘risk multiplier’ when considering the impact of changing weather patterns and more frequent and extreme weather events on built fabric. Climate change is causing the earth to warm, rainfall patterns to change and sea levels to rise: these changes increase the risk of heatwaves, floods and storm events. The Met Office has compared the UK’s 1990 climate to that projected to 2070 and they predict the following: • Winters will be between 1 and 4.5 degrees Celsius warmer • Winters will be up to 30% wetter • Winter intensity of rainfall will increase up to 25% • Summers will be between 1 and 6 degrees Celsius warmer • Summers will be up to 60% drier • Summer intensity of rainfall will increase up to 20% Extreme weather events are already more frequent and each year there is an increase in flash flood alerts when the threshold of 30 mm of rainfall per hour is achieved and storms are ‘named’. In November 2021, Storm Arwen with sustained wind and gusts of more than 90 mph from the north-east was the trigger for a 3.5 tonne pinnacle to fall from the tower at Worcester Cathedral, one of many significant fabric failures to historic buildings during storm events. Stone decays and begins to change from the moment a quarry face is exposed. The rate of that decay depends on the wider environmental conditions and the local setting of the stone. The rate of change to stone structures is generally slow, almost imperceptible if the masonry is in a sheltered location, away from pollutants and the pointing is intact and appropriate. Exposure to the weather is a known accelerator to the rate of stone decay. The acid content in rain together with cycles of wetting and drying impact on the nature of the stone. Limestones exposed to the weather soften and roughen causing the surface to become unstable and friable. Sandstones will become friable or crusts form over the surface with weak fabric behind leading to greater material loss at the point of delamination. Open joints in the masonry and friable decayed surfaces to stone allow the weather much greater purchase and result in more loss of historic fabric. Air movement plays a part in driving moisture deeper into the fabric and in the cycle of drying out, as does relative humidity, temperature and solar gain. The impact of decay to masonry structures varies from graceful uniform loss across a whole to deep pockets of acute decay punctuating the surface. Weathering stones such as hood moulds, cills and copings are designed to shed water and play a really important role in maintaining the whole structure; their decay accelerates damage to the fabric below. The most vulnerable stones are often in the most exposed positions at considerable height with ornate carved architectural delights having a lot of stone surface area, such as a crocketed pinnacle to a tower. More radical deterioration of stone structures is usually due to triggers. These Debris from a finial embedded in the roof after storm Arwen hit Worcester Cathedral (All photos: Camilla Finlay) Emergency work to restrain a finial at Worcester Cathedral weakened by storm Arwen
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