It’s getting hot: record-breaking May heat puts over 100,000 homes at risk of becoming uninhabitable

Five years on from the planning legislation changes in 2021 allowing commercial buildings to be converted into residential homes, Zurich UK warns that developers need to consider the soaring rise in temperatures to ensure that future homes are fit for changing climate conditions.

New analysis of Government planning data by Zurich UK shows that applications to convert commercial offices into residential homes in England increased from 1,025 in 2022 to 1,623 in 2025 – an increase of 58%.²

As the demand for housing stock increases, the UK is facing a growing crisis of converted homes that have not been built sustainably for these fluctuating temperatures. Already this year, the UK has recorded its hottest May since 1922³ with maximum temperatures expected to exceeded this June. Periods of extreme heat highlight a growing resilience issue, with elongated warmer spells making summers longer.

The Government plans to make it easier and faster to build new homes, with high house building targets of 1.5 million⁴ new homes this Parliament. However, whilst converting these buildings into housing stock has merits, there are growing concerns that office to residential conversions can embed long term design and structural problems if not carried out to appropriate residential standards.

Why are commercial-to-residential conversions at risk of overheating?

• Not built for living: Offices weren’t designed for 24/7 residential use
• Weak plumbing and services: Retrofits can struggle with residential demand and add heat
• Poor airflow: Sealed windows and limited ventilation trap heat indoors
• High solar gain: Large glass façades amplify heat build-up
• Little shading: Lack of external shading increases sun exposure
• Outdated fabric: Older buildings are inefficient in rising temperatures
• Regulatory gap: Many conversions fall outside modern overheating standards
• Urban heat: City locations like London intensify heat through the urban heat island effect

Megan Dunford, Zurich’s Head of Large & Complex Property Claims, said: “These challenges expand well beyond isolated periods of hot weather. While global climate patterns such as El Niño may amplify temperatures in the short term, the broader trends point to more prolonged and sustained heat events across the UK. Commercial buildings are generally designed to different operating tolerances than residential properties, and sustained temperature variation can place material stress on the building fabric. This increases the risk of thermal expansion and contraction, which may contribute to cracking, subsidence, and ultimately escape of water incidents. Over time, this not only undermines building safety and durability, but also exposes residents to higher maintenance costs and reduced living standards.”

London continues to be the worst hit by sudden temperature increase

London continues to be the least adapted to the hot weather due to the poor ventilation of offices and homes with leads to overheating.  Research by academics at The Grantham Research Institute on Climate Change and the Environment at LSE found half of all UK homes are at risk of overheating, which is projected to increase to 90% of all homes under a 2°C global warming scenario. While building regulations now address the risk of overheating in new-builds, existing buildings are excluded – despite the UK having one of the oldest and most inefficient building stocks in Europe.

Inefficiency is not the only concern; homes that are not resistant to heatwaves also pose a health risk. The Climate Change Committee estimates that heat-related deaths in the UK will increase by around 250% by the 2050s.

Reducing overheating risk

• Install solar control window film to reduce heat entering through glazing
• Add external shading such as shutters, awnings or brise soleil
• Improve ventilation, including retrofitting openable windows
• Introduce mechanical cooling or ventilation systems where needed
• Upgrade insulation and building fabric
• Use reflective materials to limit heat absorption
• Carry out overheating risk assessments during and after conversion
• Design to future climate conditions, not just current regulations

Chantelle Davidson, Zurich Resilience Solution's Head of Property Risk Engineering said: “The way buildings are constructed and how that interacts with a changing climate is becoming even more crucial. Yet, this often overlooked. Many commercial buildings were not originally intended for residential use, with materials, façades and systems designed around operational needs rather than the expectations of people living in them day to day. As a result, some features can make it more difficult to maintain a consistently comfortable indoor environment. This makes it particularly important to take a forward-looking approach at the point of design. Careful decisions around layout, ventilation, material choice and overall performance can make a significant difference when these properties are converted in how well these buildings adapt over time. By embedding resilience early, developers can help ensure converted homes can remain efficient and fit for purpose as wider environmental changes impact the built environment.”

Notes to editors

• ¹Net Additional Dwellings - Calculation of Net Change of use – PDR Office to Residential and Commercial Business and Service to Residential, Ministry of Housing, Communities & Local Government (Accessed, 28 May 2026)
• ²Data gathered from the Ministry of Housing, Communities and Local Government. PS1 District planning authorities – applications for prior approvals for permitted developments Note: On 1 Oct 2021 a separate PDR for Commercial, Business and Service to Residential Use was created which replaced Offices to Residential Use