Reducing the overheating risk in buildings

Now that we’ve turned the clocks back, watercooler chat inevitably turns to the dark nights drawing in and the onset of a prolonged cold spell.

Those long, hot summer days seem far behind us and stories of Arctic blasts and flash floods have taken over from those of record-breaking highs as the mercury rose to scorching degrees just a matter of weeks ago.

But just because we’re all starting to feel the cold now doesn’t mean we can put issues of heat out of our minds completely.

When it comes to buildings, issues of overheating are a constant consideration for designers.

A wide range of factors contribute to the risk of overheating including a high proportion of glass windows, doors and ceilings, community heating systems and insufficient natural ventilation.

And the health risk are significant for residents who can suffer stress, sleep deprivation and even premature death. The Committee on Climate Change estimates that deaths arising from overheating could rise from 2,000 per year in 2015 to 7,000 per year by the 2050s.

Now CIBSE have produced a new technical memorandum, TM59, to address the complex way buildings respond to external temperatures and present the industry with a standardised methodology to assess the overheating risk.

They hope it will become an essential checklist for all building designers to avert potential future issues.

TM59 requires designers to run simulations based on 24-hour occupancy. ‘Lifestyles change – it is now reasonable to assume that people might be at home during the day, so the design needs to be fit for purpose and acceptable at all times,’ says TM59 co-author Susie Diamond.

In live tests, researchers found the quality of glazing on certain façades needed changing to help reduce overheating, windows opening onto Juliet balconies were fitted to improve ventilation, internal blinds were installed as standard, pipes in corridors were further insulated and ventilated utility cupboards recommended.

Proposed design changes with a solution are usually accepted by architects if they don’t fundamentally change their original spec.

The Greater London Authority (GLA) is currently reviewing its guidance, with a view to adopting TM59 methodology into its energy planning guidance. Other local authorities are expected to follow suit.

The major difference between GLA’s current guidance on overheating i.e. CIBSE TM52 and future guidance of TM59 is the weather files, as TM59 considers the wider impact of adverse summer weather temperatures for a 2020 high emissions scenario as opposed to Design Summer Year (DSY) which is the current practice. This means that the schemes should be designed appropriately to cater for extreme weather conditions and also design a collaborative strategy to mitigate overheating from the space. This includes careful planning on type and size of glazing, ventilation, shading devices, window opening etc.

We welcome this standardised assessment tool and you’ll find our team happily discussing its benefits as they chat in all weathers at our equivalent of the watercooler – the kitchen taps!

TM59 can be downloaded for free on the CIBSE site.