Britain's private rented sector has spent a decade fixated on keeping tenants warm. Now regulators, insurers and campaigners are asking the opposite question: how hot is too hot? Simply Business's investigation into overheating rental properties lands at a pivotal moment, with the Housing Health and Safety Rating System silent on maximum indoor temperatures even as summer heatwaves become a near-annual feature of UK life. For an industry that has just absorbed the cost of EPC upgrades and is bracing for Awaab's Law reforms, the prospect of a new heat-safety obligation is not a footnote - it is the next major compliance front.
The regulatory gap is stark. Under HHSRS, excess cold is a recognised category one hazard, giving councils clear grounds to act against landlords whose properties fall below roughly 18°C. There is no equivalent trigger for excess heat, despite Office for National Statistics data linking heat-related mortality spikes to the 2022 and 2023 summers, when parts of London and the South East recorded internal temperatures above 30°C in top-floor flats and converted lofts. Building Regulations Part O, introduced in 2022, now requires new-build homes to be assessed for overheating risk - but that standard applies only to new construction, leaving the millions of Victorian terraces and 1960s-70s tower blocks that dominate the private rented stock in cities such as Manchester, Birmingham and Leeds entirely outside its scope.
This matters enormously for buy-to-let landlords because the properties most exposed to overheating risk are often the same ones that have just been retrofitted for energy efficiency. Cavity wall insulation, double glazing and draught-proofing - all incentivised through EPC targets - trap heat as effectively as they retain it, turning well-insulated flats into summer ovens. Landlords in London's high-density boroughs, where south-facing new-build apartments with floor-to-ceiling glazing have proliferated over the past decade, face a particular exposure. Estate agents in Nine Elms and Stratford have already reported tenant complaints about un-openable windows and inadequate ventilation, issues that could become actionable once a formal overheating standard exists.
The precedent everyone in the sector is watching is Awaab's Law, which from October 2025 begins imposing strict repair timelines on landlords for damp and mould hazards, with excess cold and, eventually, excess heat expected to be folded into subsequent phases of the reform. Housing associations and larger institutional landlords are already commissioning thermal comfort audits ahead of that extension, and the smart money among professional landlords is to get ahead of the curve rather than wait for enforcement. Retrofitting external shading, upgrading to low-e glazing with better solar control, and installing mechanical ventilation with heat recovery are no longer just ESG box-ticking - they are becoming risk-management necessities that will separate compliant portfolios from exposed ones.
Regional variation will shape how urgently this bites. Northern cities such as Newcastle and Liverpool, with older housing stock, thicker masonry walls and lower average summer temperatures, face materially less immediate risk than London and the South East, where urban heat island effects can add 4-5°C to ambient temperatures in dense boroughs. Surrey's commuter-belt new-builds, many constructed with large glazed elevations to maximise natural light, sit in an awkward middle ground - well insulated, thermally efficient in winter, but potentially non-compliant with any future summer comfort threshold. Developers currently designing schemes for delivery in 2027 and beyond would be prudent to model overheating risk now, given the lag between Part O's introduction and its likely extension to a formal rental sector standard.
For first-time buyers and owner-occupiers the calculus is different but not irrelevant: resale values for properties later identified as chronic overheating risks could soften, particularly for top-floor flats and glass-heavy new-builds lacking effective solar shading. Commercial investors backing build-to-rent schemes should treat this as an underwriting variable alongside energy performance certificates, since institutional funds increasingly price ESG and habitability risk into acquisition due diligence. Over the next six to twelve months, expect the English Housing Survey and forthcoming government consultations on decent homes standards to formally address summer overheating, likely drawing on the World Health Organization's guidance that indoor temperatures above 24°C for sustained periods pose measurable health risks to vulnerable occupants.
The direction of travel is unambiguous: overheating will follow the same regulatory arc as damp and mould, moving from an informal tenant grievance to a statutory hazard with enforcement teeth within this parliament. Landlords who treat the current absence of a legal maximum temperature as a permanent exemption are misreading the market. Those who invest now in passive cooling measures - external shutters, reflective glazing, cross-ventilation retrofits - will protect both tenant wellbeing and asset value ahead of a regulatory shift that is no longer a question of if, but when.
