Hot topic: Legal, regulatory and insurance implications of overheated buildings

Overheating in buildings raises serious issues for the construction sector and its insurers. Here’s our guide to the legal framework and what’s on the horizon.

Rising heat: The growing problem

As our climate warms and urban areas become denser, many buildings, especially those which are highly insulated with windows that trap in the sun’s heat, struggle to stay cool. What was once considered energy-efficient design, now contributes to indoor environments that are uncomfortably, and sometimes dangerously, hot. Heat produced from under-designed services, such as ventilation or hot water systems, can also contribute to the problem.

All of this raises questions about how we design, retrofit and regulate buildings in a changing climate. Yet, despite all of this, there is no maximum internal temperature in the Building Regulations 2010 (Building Regulations), nor in the UK health and safety guidance.

Building Regulations 

Parts O (Overheating), F (Ventilation) and L (Conservation of Fuel and Power) of Schedule 1 of the Building Regulations include certain amendments which apply to projects where construction started on or after 15 June 2023. They are supported by technical guidance in, respectively, Approved Documents O, F and L.

Approved Document O focuses on overheating mitigation in new residential buildings. It outlines two routes to compliance with Part O:

• Simplified method – This sets: (1) maximum glazing areas based on façade orientation and geographical location; (2) shading requirements such as external blinds; and (3) purge ventilation requirements such as openable window area. However, if acoustic or air quality issues prevent opening windows, this method cannot be used.
• Dynamic thermal modelling – This uses simulation software to predict overheating risk and demonstrate comfort thresholds under future climate scenarios. Rather than relying on glazing and ventilation limits, it supports innovative solutions like mechanical ventilation or hybrid cooling.

Approved Document F provides guidance on ventilation requirements to maintain good indoor air quality and prevent issues like condensation and mould. It is split into dwellings and other buildings. Requirements are met if the building has ventilation that achieves certain objectives such as extracting water vapour and pollutants while ensuring low levels of noise and protection from draughts.

Approved Document L provides guidance on energy efficiency. It too is split into dwellings and other buildings. Key requirements include limiting heat gains and losses through the building fabric and services (such as the boiler and hot water storage), and generating on site-electricity if appropriate equipment is installed.

Future Homes Standard and Future Buildings Standard 

Moving forward, the Future Homes Standard introduces stricter energy efficiency and carbon reduction targets for new homes. The Future Buildings Standard is similar but applies primarily to new non-domestic buildings such as offices and schools. Both apply only to England and build on Parts L and F of the Building Regulations. While the current focus is on heat retention, future versions may address cooling more directly. 

For both Standards, the final regulations are due to be published this autumn and come into effect in December 2026, with full compliance in January 2028.

Defective Premises Act

Overheating in residential properties may give rise to claims under section 1 of the Defective Premises Act 1972 (DPA). The DPA requires those “taking on work for or in connection with the provision of a dwelling” to ensure the work is done in a professional or workmanlike manner so the dwelling is “fit for habitation”. Overheating can cause health risks or serious discomfort and, as a result, render a property “unfit for habitation”.  

This situation is of some concern as a direct result of the extended limitation periods set out in the Building Safety Act 2022. For claims brought under section 1 of the DPA, limitation has now been extended from six to 30 years for dwellings completed before 28 June 2022, and 15 years for those completed afterwards.

This may open the door to historic overheating claims. There is significant debate as to whether courts may effectively adopt a “strict liability” approach to DPA claims, focusing on the outcome (fitness for habitation) rather than the process. This is despite there being little appreciation by most engineers and architects about overheating risks in the 1990s and even the 2000s.

Arguably, the standard of design, materials and workmanship is to be judged by reference to the skill and care expected of the competent professional at the date of work. Back in the 1990s and 2000s, the focus was on energy efficiency and minimising heat loss.

At that time, the concept of buildings overheating was less broadly considered than today and, in many respects, overheating was likely expected to be a rare occurrence (ie, an unusually hot summer day). Sustained “heat waves” were less of a consideration, and the expectation that they would or may become the “norm” may not have been within the reasonable contemplation of building designers at the time.

Conversely, if the key hurdle for a claimant is for it to establish “unfitness for habitation”, it may not be a defence if the designer or builder acted with reasonable skill and care. Arguably, there might be a breach of the DPA even if the professional acted with reasonable skill and care all the way back in the 1990s. 

We’ve not identified any reported DPA cases specifically on overheating. However, our sense, from the cases we have been involved in, is that the strict liability argument, or something close to it, is being more readily accepted. But it’s a case of watch this space.

Preparing for a warmer future 

There is a growing expectation to design and construct buildings fit for the future with green initiatives in mind, which not only conserve heat in the winter but also prevent overheating in the summer.

That requires innovative solutions, such as building materials with high thermal mass and good insulation properties, together with proper shading and ventilation, to ensure the best all-year-round performance, no matter what the season. Air source heat pumps are another solution. Modern ones not only use less electricity than gas or oil boilers for heating in the winter, but tend to reduce energy waste compared to typical air conditioners for cooling in the summer.

Currently, standard JCT contracts do not define “overheating” or “thermal comfort” or set temperature limits. If employers want to address overheating head-on, rather than simply rely on the obligations prescribed by the Building Regulations, they could look to set out their requirements in the Employer’s Requirements.

In the future, the Building Regulations may introduce more comprehensive requirements for overheating mitigation. This may impact how bespoke contracts set out overheating and thermal comfort standards. Future iterations of standard forms like the JCT could also incorporate new sustainability and wellbeing provisions.

However, if you design buildings to be super sustainable and address the user’s “internal climate” needs, that can massively increase the build cost and impact on developers’ profit margins. So, the construction industry may have to tread a careful balancing act with one eye on meeting obligations and avoiding claims, and another on the commercial reality. Offsite and modular building techniques may become more common to meet standards efficiently.

When it comes to market pressures, insurers are in a similar boat to potential insureds as both face increased regulatory and societal scrutiny of their approach to climate change. Green initiatives can include new building techniques and materials to address overheating, but newness can create its own risks of things going wrong which in turn can lead to claims.

One thing that is fairly certain, is that climate change will continue to drive regulatory reform with greater emphasis on thermal modelling, passive cooling and stricter compliance checks to address overheating. Engaging with upcoming standards, revisiting contract terms and reassessing risk exposure will be key to navigating the warming landscape.

This article forms part of our Breaking Ground series. For more information on the series, contact Andrea Lynch or Neil Howes.