I sat down recently with BBC London's Alice Bhandhukravi to talk about a problem that's quietly shaping homes across the capital: overheating. Only a small part of that conversation made the broadcast, but we spent the best part of an hour on why so many London homes are now too hot in summer, and what architecture can do about it.
It's something we think about constantly at RISE, and not as a problem to solve with expensive kit. Most of the answer is in climate-responsive design: the decisions about orientation, shading and ventilation that make a house comfortable without leaning on mechanical cooling.
Sean Ronnie Hill of RISE Design Studio, interviewed by BBC London on how better design can reduce the risk of overheating in the capital's homes. RISE Design Studio.
Much of London's housing was never built for the climate we now have. Victorian and Georgian houses were made to breathe: open fireplaces kept air moving, single glazing leaked heat, and high ceilings let warmth rise away from the rooms people used. They were inefficient in winter, but surprisingly tolerant of heat in summer.
Over the last twenty years, a lot of those houses have been sealed up in the name of energy efficiency. Draught-proofing, double glazing, insulated roofs and airtight construction have transformed their winter performance. But without matching attention to ventilation, shading and solar control, many of them now struggle in the warmer months.
Large glazed extensions facing west or south-west, unshaded rooflights, dark roof finishes and exposed thermal mass all push in the same direction. In a long heatwave, a house absorbs heat all day and releases it slowly into the evening, exactly when people are trying to sleep. The result is familiar across London now: bedrooms that stay too warm well into the night.
The problem is also urban. London has a pronounced heat island effect, where dense expanses of asphalt, brick, concrete, paving and dark roofs soak up heat during the day and give it back slowly after dark. Areas with few trees and little open ground stay markedly warmer overnight than greener parts of the city.
Kilburn, where we've worked on several projects, is a good example. In a summer heatwave its night-time temperatures can sit well above those a short distance away in Regent's Park, where mature trees, planting, open ground and evaporation cool the local air. For anyone in a top-floor flat, a poorly ventilated terrace, or a heavily retrofitted house with no external shading, that's a real and growing discomfort, not a distant one.
The irony is that the most effective cooling ideas aren't new. Around Barcelona, southern Spain and much of the Mediterranean, buildings evolved over centuries to handle heat without machinery. Deep balconies threw shade, external shutters stopped sunlight before it reached the glass, recessed openings cut solar gain, and tall rooms encouraged air to move. None of it was decorative. It was a response to the climate.
We draw on the same principles when we design and retrofit in London. The measures that tend to work are external shading that intercepts sun before it reaches the glass, such as a brise soleil, pergola, canopy or deep overhang; external blinds or shutters, which beat internal ones because they stop the heat outside the building; opening windows positioned to drive cross ventilation; rooflights placed to purge hot air by stack effect; restraint with unprotected south-facing glazing; and planting around the house to add shade and a little evaporative cooling. Passive design isn't primitive. Most of the time it's simply the smarter option.
We model how a building will behave long before anything is built, using detailed environmental simulations and digital twins. That lets us test how sun, airflow, shading and thermal mass interact across the year: analysing peak summer solar gain, seeing how external shading changes internal temperatures, simulating airflow through stairwells and rooflights, finding the rooms most at risk of overheating, and comparing options before any expensive decisions are committed on site. The point is to design the comfort in from the start, rather than relying on mechanical systems to paper over an avoidable problem later.
Technology has a real role. Air-source heat pumps, MVHR, intelligent controls and high-performance glazing all help. But they work best alongside good passive design, not as a way to compensate for poor orientation or too much glass. Our order of priority is usually passive measures first, efficient systems second, and conventional air conditioning only where it's genuinely needed.
That order matters beyond any single house. Conventional air conditioning uses a lot of electricity and dumps waste heat into streets that are already too warm, so the more homes that install it, the hotter the city gets. Architecture should be reducing the need for cooling rather than treating it as the default.
Overheating is becoming one of the defining design problems for cities. The homes that perform best over the next fifty years won't necessarily be the ones with the most technology. They'll be the ones that face the right way, shade themselves, ventilate naturally and respond to the climate around them. Comfort isn't a luxury bolted on at the end. It's one of the things good design is supposed to deliver in the first place.
If you're worried about overheating in your home, or planning a renovation or extension and want to get ahead of it, we'd be glad to talk it through.
→ Or call the studio on 020 3947 5886
Why does my house overheat now when it coped fine years ago?
Two things have usually changed. The house has often been sealed up over the years (draught-proofing, double glazing, insulation, airtightness) to improve winter performance, and unless shading and ventilation were addressed at the same time, that traps heat in summer. At the same time, summers themselves are hotter, and in a dense city the heat lingers overnight.
Does adding insulation cause overheating?
Insulation on its own doesn't, and a well-insulated house holds a steady temperature. The problem comes when insulation and airtightness are added without matching shading, solar control and ventilation. Insulation keeps heat out as well as in, but only if the heat isn't being let in through unshaded glass in the first place. The fix is to treat fabric, shading and ventilation as one job rather than separate upgrades.
What's the most effective way to stop a room overheating?
Stop the heat before it gets in. External shading, a brise soleil, shutters, a deep overhang or a pergola, is far more effective than anything fitted inside, because once sunlight has passed through the glass the heat is already in the room. After that, ventilation that lets hot air out, particularly at night, does most of the rest.
Are external blinds really better than internal ones?
Yes, and it's not a small difference. External shutters and blinds block the sun before it reaches the glass, so the heat never enters the room. Internal blinds only intercept it once it's already inside, so they help with glare but do little for temperature.
Will a glazed or south-facing extension overheat?
It can, and large west or south-west-facing glass is one of the most common causes of overheating we see. That doesn't mean avoiding glazing, it means sizing and orientating it sensibly, shading it externally, and giving the space a way to purge hot air. These are decisions best made at design stage, when they cost nothing to get right.
Do I actually need air conditioning?
Usually not, if the building is designed well. Our order of priority is passive measures first, efficient systems like MVHR and heat pumps second, and conventional air conditioning only where it's genuinely unavoidable. Beyond the running cost, AC dumps heat into the street outside, which makes the wider problem worse the more people install it.
Is overheating covered by building regulations?
For new homes in England, yes. Approved Document O has set overheating requirements for new residential buildings since June 2022, with compliance shown either through a simplified method or dynamic thermal modelling, and passive measures have to be exhausted before mechanical cooling is allowed. It does not currently apply to extensions or conservatories added to existing homes, which is where a lot of the real risk sits, so on that work it's worth applying the same thinking voluntarily.
Can overheating be fixed in a house that already has it?
Often, yes. External shading, better cross and stack ventilation, lighter or reflective roof finishes, and planting around the house can all be retrofitted. The first step is working out exactly where the heat is coming in, which is where modelling an existing house helps, so the money goes on the measures that actually move the temperature.
If you're concerned about overheating in your home, or planning an extension or renovation and want to understand more reach out:
→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886
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