Life inside a heat trap

As we discussed in a previous Blog Post, groups of tall buildings are prone to the Urban Heat Island (UHI) effect – which happens because materials like concrete and asphalt absorb and retain heat. A recent headline caught our eye. It refers to what happened last June when a warning was stuck to the window of a flat in Leaside Lock, East London, reading: “DO NOT BUY THESE FLATS. TOO HOT.”

The photo has been shared over half a million times:

Picture Credit: Aidan Sheehan

Twelve months later, after the UK recorded its second-warmest June and fifth-hottest July since records began in 1884, residents in the tallest, south-facing block say nothing has changed. ‘When I’m trying to fall asleep at night, it gets quite unbearable,’ said one student living near the top of the 28-storey building. His only relief? ‘All I can do is open the window.’

The perfect recipe for overheating

Leaside Lock is in Tower Hamlets - the UK’s most densely populated borough, where 81% of households live in purpose-built flats, double the London average. Since 2014, the skyline has been transformed: 71 new towers of 20 storeys or more have gone up. However, the borough also ranks poorly for green space. The result is a "hot box" effect: dense buildings, little shade, and materials that trap heat.

It’s not just bad luck - it’s in the design.

Why new-build flats get so hot:

• Airtight insulation: modern energy-efficiency standards mean that walls and windows are sealed tight to keep in winter warmth. But in summer this traps heat inside. Without adequate mechanical ventilation, the indoor temperature climbs relentlessly.
• Large, unshaded windows: expansive glazing - often marketed as a feature - acts like a greenhouse. South- and west-facing windows can push indoor temperatures past 30°C.
• Single-aspect layouts: many flats have windows on just one wall, making cross-ventilation impossible. Even with windows open, there’s no airflow to flush out heat.
• Communal heating systems: piped hot water for the whole building can leak residual heat into corridors and walls year-round, raising baseline temperatures.
• Urban heat island effect: dense clusters of concrete and asphalt absorb heat during the day and radiate it back at night, preventing natural cooling.

No easy solution

Up the road from Leaside Lock, at the Three Waters development, a 41-year-old SEND teacher described her experience: ‘Our temperatures haven’t gone below 27°C over the past two months. This summer, the thermometer hit 33°C.’

The heat causes headaches, exhaustion, and fatigue. Opening windows brings noise and dirt from the busy A12. No trees stand beside the block to offer shade.

The UK Green Building Council calls street trees a ‘simple, cost-effective’ cooling solution - but developers have often favoured maximising building footprints over planting greenery.

A spokesperson of Peabody, which manages Three Waters, said: ‘We work with construction partners to ensure homes are designed with ventilation and shading in mind… Since 2022, we’ve added features like external shutters and are trialling materials that keep homes cooler in summer and warmer in winter.’

When the heat becomes a health risk

Kestrel House, a 55-metre council block in Islington, has its own history of sweltering summers. Residents there report summer temperatures rarely below 27°C, peaking at 35°C in past heatwaves. Friends of the Earth rank Islington second only to Tower Hamlets for population density, with just 2m² of green space per person.

Hot homes aren’t just uncomfortable. They kill indirectly. During the 2024 heatwaves, deaths from influenza and pneumonia were 13% above the seasonal average; deaths from circulatory diseases, dementia, and Alzheimer’s rose by 11%. For vulnerable residents, sustained indoor heat can trigger or worsen heart and lung conditions, disrupt sleep, damage mental health, and cause heat exhaustion.

Overheating hits low-income and minority ethnic communities harder

The risk isn’t evenly spread. Research shows:

• 48% of the poorest fifth of households in England live in homes at high risk of overheating, compared with 17% of the richest.
• Minority ethnic households are disproportionately affected, often living in urban high-density areas with less access to green space.
• Social renters face the greatest exposure: around two-thirds live in at-risk homes, versus 17% of owner-occupiers.

These households are also less able to afford active cooling like portable air conditioning, and are less likely to have control over building upgrades. The overlap between poor housing quality, dense city living, and environmental inequality is stark - a form of climate injustice hiding in plain sight.

The UK’s housing system is unprepared for climate change

Experts warn that the UK’s housing stock, both old and new, is dangerously unfit for the hotter summers that climate change is bringing. Many homes were designed for mild weather, with regulations historically focused on preventing cold and damp, not heat stress.

The government’s Future Homes Standard, due in 2027, promises lower carbon emissions and better insulation, but critics say it doesn’t go far enough on summer overheating. Without stronger rules, we risk locking in thousands more homes that will be unsafe in 30-degree heat.

What can be done: now and in the future

There’s no single fix, but a combination of design, planning, and retrofitting can make a big difference.

For new builds:

• Passive cooling design: orient buildings to minimise direct summer sun, using smaller or recessed south-facing windows, and incorporating overhangs or brise-soleil.
• External shading: shutters, louvres, and blinds on the outside of windows block heat before it enters, which is far more effective than internal blinds. (Currently, only 11% of English households use shutters, compared to 91% relying on open windows.)
• Cross-ventilation: avoid single-aspect flats; include openable windows on opposite sides of a unit for natural airflow.
• Thermal mass: use materials that absorb heat during the day and release it slowly at night, smoothing temperature swings.
• Green infrastructure: plant trees, green roofs, and shaded public spaces around developments.

For existing homes:

• Retrofit shading and ventilation systems.
• Apply reflective coatings to roofs and facades.
• Add mechanical ventilation with heat recovery systems that can also remove summer heat.
• Expand urban tree planting to cool entire neighbourhoods.

Crucially, these measures must be targeted at the areas where density, lack of greenery, and social inequality intersect.

Beyond the building: a systems problem

Overheating homes are a symptom of a bigger issue: our cities and housing policies haven’t caught up with climate reality. As average summer temperatures rise and extreme heat events become more frequent, adaptation can’t be an afterthought. It must be designed into every home, every street, and every borough plan.

For residents of Leaside Lock, Three Waters, and Kestrel House, this summer has been another season of sleepless nights and stifling days. Without urgent action, many more will join them in the years ahead.

Hot homes shouldn’t be a badge of modern housing. They’re a sign we’ve built for the wrong climate - and a warning we can’t afford to ignore.

Carl Dodd, Property Revolutions Ltd.