How Hot Is Too Hot? Overheating Is Becoming an Everyday Compliance Problem

Since June 2026, councils in England have had stronger powers to act on serious hazards in rented homes. Penalties can reach £7,000 per hazard and rise to £40,000 where a landlord fails to act on a formal notice. Tenants may also pursue a separate rent repayment claim through the courts.

Overheating sits on the same list of 21 hazards under the Housing Health and Safety Rating System (HHSRS), as damp, mould and excess cold. Tenants already have the right to complain about excessive heat and request a formal inspection.

The scale of the issue is growing. In 2024, 12% of occupied homes in England reported overheating—around three million homes, compared with 7% in 2019.

The consequences are not confined to discomfort. The UK Health Security Agency’s interim report recorded 2,877 heat-associated deaths across England and Wales during the May and June 2026 heatwaves, close to the 2,985 recorded across the whole of 2022.

Yet England still has no fixed legal maximum temperature for a home.

That leaves landlords, housing providers, councils, surveyors and designers with a more difficult question:

Without a single legal temperature limit, how do you prove that a home presents a genuine overheating risk?

A hot reading is not the same as evidence of a hazard

HHSRS was deliberately designed without a fixed overheating threshold. The assessment is not based on one temperature figure. It considers whether conditions create a genuine health risk, taking account of the dwelling, the duration and likelihood of exposure, and the vulnerability of the occupant.

A short inspection can establish that a home is hot at that moment. It is much less effective at showing:

• whether the problem affects one room or the whole home;

• whether heat is confined to a short afternoon peak or continues overnight;

• whether the building cools when outdoor conditions improve;

• whether temperatures are progressively building over several days; and

• whether opening a window would provide a practical solution.

This matters to both sides of an enforcement decision. A council needs defensible evidence before taking action. A landlord or housing provider needs equally robust evidence to demonstrate that a genuine problem is being addressed—or that conditions are less severe than a single reading might suggest.

Neither side is well served by a snapshot.

The case: a flat that could not cool down

The case study involved an ordinary mid-terrace, two-bedroom flat built around 2010, with gas heating.

Six rooms were monitored for 12 days during late June and early July 2026. Temperature and humidity were recorded every 15 minutes using our remote monitoring technology.

The headline result was striking:

Every room except the bathroom remained at or above 26°C for eight consecutive nights—67% of the monitoring period.

The main bedroom reached an air temperature of 29.0°C. When humidity was taken into account, the apparent or “feels like” temperature was approximately 31.5°C.

Humidity matters because the body relies heavily on the evaporation of sweat to cool itself. As humidity rises, evaporation becomes less effective. The air temperature may remain unchanged, but the physiological heat load increases.

That effect is particularly important indoors overnight, when air movement may be limited and the body needs to lower its temperature to sleep effectively.

However, the most important finding was not the peak temperature. It was the flat’s repeated failure to cool.

The weather cooled. The flat did not.

During one comparatively mild day, the outdoor temperature never exceeded 23.5°C and fell to an overnight low of 14.5°C. Cooler outdoor air was therefore available.

Despite this, five of the six rooms did not fall below 26°C at any point during the day or night.

The clearest example occurred following the hottest outdoor day of the monitoring period. The external temperature peaked at 32.0°C at 17:45. Five hours later, the outdoor temperature had fallen to 24.5°C. Indoor temperatures remained between 27.5°C and 29.0°C—between 3.0°C and 4.5°C warmer than the air outside.

The main bedroom barely cooled during this period. Its temperature fell by no more than 0.5°C while the external temperature dropped by almost 8°C.

The pattern also failed to reset overnight.

By the end of the 12-day period, daytime peaks were approximately 2.0°C to 3.0°C higher than at the beginning. Overnight minimum temperatures had also risen by approximately 2.0°C to 3.0°C across all six rooms.

This was not simply a flat becoming hot during hot weather. It was retaining heat faster than it could release it. Eventually, the property no longer required extreme outdoor temperatures to remain excessively warm.

Why duration and recovery matter

A single peak temperature would not have revealed this pattern.

The monitoring evidence showed:

• repeated exposure across consecutive nights;

• a problem affecting almost the entire home;

• limited response when outdoor temperatures fell;

• continued overheating during milder weather; and

• progressive heat accumulation across the monitoring period.

Those findings reframe the question for a surveyor or environmental health professional.

The question is no longer simply: Was the property hot?

It becomes:

Why did a property with repeated opportunities to cool down fail to take them?

That is a building-performance question, not just a weather question.

Would opening a window have solved it?

Advice to open windows can sound reasonable, but it needs to reflect the actual property.

In this flat, modelled cross-ventilation through two openings indicated that most rooms could return to a comfortable temperature before midnight in approximately two hours.

Using a single open window was modelled to take between six and nine hours.

That difference matters.

A cooling strategy that works theoretically but cannot cool a bedroom until the early morning is unlikely to provide a practical response to repeated overnight overheating.

It also illustrates why monitoring should consider not only whether cooler air was available, but whether the building had a realistic and usable route for bringing that air through the home.

Secure night-time openings, cross-ventilation routes, external shading and, where necessary, mechanical ventilation or cooling may all need to be considered.

What the evidence proves—and what it does not

Monitoring data does not, by itself, complete an HHSRS assessment or establish a formal hazard score.

That judgement remains with a competent assessor. A physical survey is also required to identify why the building behaves as it does.

Monitoring can, however, provide something much more useful than a single temperature reading: a precise and defensible account of what happened, where it happened, how long it lasted and how the building responded when conditions outside improved.

In this case, the evidence can help the surveyor focus on the right questions:

• Why is heat being retained?

• Are effective cross-ventilation routes available?

• Can windows be opened securely overnight?

• Is solar gain contributing?

• Would external shading make a meaningful difference?

• Is mechanical ventilation or cooling justified?

The monitoring narrows the investigation. The physical survey establishes the cause.

Retrofit was built for winter. It must now survive summer.

The wider issue is not limited to one flat.

For decades, homes have been insulated, draught-proofed and sealed to reduce winter heat loss. That work remains essential. Cold and expensive-to-heat homes continue to present serious health and affordability risks.

Insulation and airtightness are not the villains.

The more precise question is whether a home can retain winter warmth without trapping summer heat—and whether occupants have a safe, practical and genuinely usable way to release that heat.

A resident cannot always solve a building-performance problem by opening one window and hoping for the best.

As overheating complaints increase and enforcement powers become stronger, decisions will increasingly need to be based on evidence rather than assumption.

The cost of getting that judgement wrong has risen considerably.

The wider question is how many other homes are quietly behaving in the same way: accumulating a little more heat each day, failing to recover overnight, and leaving occupants exposed long after the weather outside has begun to cool.

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Sources

• Ministry of Housing, Communities and Local Government, English Housing Survey 2024–25: Weather Resilient Homes Fact Sheet, 9 July 2026.

• UK Health Security Agency, Interim Heat Mortality Monitoring Report, England: May and June 2026.

• UK Health Security Agency, Heat Mortality Monitoring Report, England: 2024.

• UK Health Security Agency, Heat Mortality Monitoring Report, England: 2025.

• Shelter Legal England, Local Authority HHSRS Enforcement Action.

• Landlord Today, Legal Warning Over Tenants and High Temperatures, 26 June 2026.

• PropertyWire, Landlords Face £7,000 Fines Over Overheating Hazards.

• Met Office, seasonal and heatwave weather summaries.

• Ministry of Housing, Communities and Local Government, Dwelling Stock Estimates, England: 31 March 2024.