Rethinking retrofitting for historic buildings
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On Sunday, I joined a team of AECOM employees cycling from London to Glasgow for the 2021 United Nations Climate Change Conference, also known as COP26. This awareness-raising ride began in central London, at the Palace of Westminster, the seat of both British Houses of Parliament and a historic building dear to many of us in the UK. It had been rebuilt after being devastated by the Great Fire of London in 1834 and has been subject to several renovation projects since. Shortly afterwards, we rode past Buckingham Palace. The official residence of the British Monarchy since 1837 has been extended, refaced and refurbished many times since and is currently undergoing a complete overhaul of key infrastructure.
This got me thinking about the challenge of making storied buildings like these energy efficient – and whether we need to rethink our approach given the magnitude of the climate crisis.
The UK has the oldest housing stock in Europe, according to The BRE Trust, a charity dedicated to improving the built environment, possibly the world. Heritage buildings are challenging to retrofit because of the need to preserve their heritage features. and due to their traditional construction, standard retrofitting approaches also aren’t sufficient.
The first challenge is often the energy rating measured by a U-value, which scores how easily heat can pass through materials, and by a g-value, which assesses how much solar heat is allowed through. Due to the heritage of the building, it isn’t always possible to put insulation on the outside, which is the ideal place, without affecting its distinct façade. Insulation can be installed on the inside, but this reduces the building’s footprint and can lead to issues with condensation.
Another challenge is how to reduce the air leakage of the heritage building, which requires significant renovation to reach a standard similar to new ones. There are also issues with how the buildings are heated and cooled. Heritage buildings generally have limited floor to ceiling heights, so it can be difficult to fit the required equipment, such as heat pumps. There are also often limited locations for heat pumps to be located externally due to the need to preserve the building’s external appearance.
Power to the building also needs to be considered. New buildings are now installing photovoltaic (PV) panels on the roof to provide renewable electricity to the building – but this is almost impossible without impacting the heritage look.
Now I’m a huge fan of heritage buildings, visiting many in my spare time. Going forward, however, we need to rethink our approach in favor of making them more energy efficient. Heritage glass in windows, for example, could be replaced with slim line double glazing so it still has the appearance of a single glazed window. High performing insulation can be used to minimize the reduction in building footprint. District heating systems could be used instead of heat pumps, and PV panels sourced that can be integrated into the roof to reduce the visual impact – such things do exist!
Of course, it’s often much more expensive to retrofit old buildings because of the need to preserve the traditional appearance, which involves significant costs to owners. Given that 20 percent of UK housing stock was built over 100 years ago, financial incentives may be required if we are to meet our net zero carbon goals. Heritage bodies should also reflect on their approach to allow a little more flexibility, preserving the integrity of these heritage buildings while making them also a part of the solution towards reaching net zero.