As this week’s heat builds across the South East – England has just recorded its warmest June on record, and we’re now into the third official heatwave of the year – it’s worth pausing to look at what’s actually happening inside the new homes being built and occupied right now. Many of them were designed under Approved Document O (AD-O), the overheating regulation that came into force in 2022. Fewer of them, we’d argue, were designed with proper thought given to what that regulation does to the acoustic environment inside.
What Approved Document O actually asks for
Part O requires new residential buildings to limit unwanted solar gains and provide ways to remove excess heat. In practice, most schemes discharge this obligation one of two ways: the simplified method, which caps glazing areas and demands a minimum amount of openable area for cross-ventilation or single-sided ventilation; or dynamic thermal modelling, which allows more design flexibility but still, in the overwhelming majority of cases, relies on openable windows as the primary heat-removal strategy.
That’s the crux of the issue. Overheating strategy and natural ventilation strategy are, in most current designs, the same strategy. The regulation assumes people will open their windows when it’s hot.
Why that collides with acoustics
Most housebuilding in England is happening in locations that are not acoustically quiet: alongside busy roads, near railway corridors, under flight paths, in dense urban infill sites, next to industrial or leisure noise sources. Facades on these sites are typically designed – under Building Regulations Part O and Part F, and under planning conditions informed by BS 8233 and the WHO guidelines on environmental noise – on the assumption that windows will be closed, with background ventilation coming through acoustic trickle vents and internal noise levels controlled by the glazing specification.
Approved Document O effectively asks for the opposite assumption in hot weather: windows open, often fully, often for extended periods, sometimes overnight to purge heat before the next day’s solar gain begins. On exactly the nights when people most need to keep a window open to stay cool and get some sleep, external noise levels from traffic and other sources are often at their least forgiving, because the alternative is discomfort or worse, heat-related sleep disruption and health risk.
Put simply: the mitigation for one Part of the Building Regulations can create the failure condition for another.
Where our scope of work sits
This is the specific problem our consultancy is set up to solve, and it needs to happen early, ideally at the same time as or before the overheating strategy is being developed rather than as a retrofit once a scheme has already been designed around a particular glazing and ventilation approach. Our work typically covers:
- Facade and glazing acoustic design that accounts for a realistic proportion of open-window hours during warm weather, not just the closed-window baseline case
- Assessment of external noise levels at openable elements, including night-time train and road traffic profiles, so that overheating-driven ventilation strategies are tested against real acoustic exposure, not assumed away
- Acoustic ventilator and trickle vent specification sized to deliver the free area Part O’s dynamic modelling or simplified method requires, without undoing the sound insulation the facade has been designed to achieve
- Mechanical ventilation and cooling alternatives where openable-window strategies simply cannot deliver both thermal comfort and acceptable internal noise levels – increasingly relevant on the noisiest sites, where MVHR or comfort cooling may be the only way to satisfy both regulations simultaneously
- Joint thermal-acoustic reporting for planning submissions, so that overheating strategies and noise assessments are presented as a coordinated position rather than two separate documents that quietly contradict each other
Why this matters commercially, not just technically
For architects and developers, the risk here isn’t abstract. Overheating and noise complaints are two of the fastest-growing categories of post-occupancy dispute in new residential stock, and building control, planning authorities and NHBC-style warranty providers are increasingly alert to schemes where the two haven’t been considered together. A dwelling that technically discharges both conditions on paper but leaves occupants choosing between a hot bedroom and a noisy one is a dwelling that generates complaints, remedial costs, and reputational damage – often years after practical completion, when it’s far more expensive to fix.
Getting this right at RIBA Stage 2–3, when glazing ratios, ventilation strategy and facade buildup are still being decided, costs very little relative to the alternative. Getting it wrong means retrofitting acoustic ventilators, secondary glazing or unsustainable mechanical cooling into completed buildings, usually under pressure, usually at the developer’s expense.
The moment to act is now, not just in a heatwave
It’s tempting to treat this as a talking point only when the mercury climbs, as it has done three times already this year. But the design decisions that determine whether a home is liveable in a heatwave – and quiet enough to sleep in when the windows are open – are made months or years before anyone feels the heat. Every scheme currently at design stage will, at some point in its life, face a week like this one. The question worth asking now is whether it’s been designed to cope with both problems at once, or just one of them.
That’s the conversation we’d encourage architects, housebuilders and developers to have earlier in the process. It’s a more straightforward one to have at the drawing board than it is on site, or in a residents’ meeting, the next time the temperature hits 34 degrees.
