In our previous blog article, we discussed how overheating can result in poor indoor air quality in dwelling, and can in turn pose a range of health risks, while also being detrimental to the environment and incurring unnecessary expense.

The benefits in choosing a building design that avoids overheating are many, however, there’s not an Act or legally binding, more a minimum standard that should be met. This article will look in detail at the UK building regulations and what they have to say concerning the mitigation of overheating in residential properties.

What risk does overheating pose?

The UK government has set itself the target of achieving net zero by 2050. As part of this Net Zero Strategy, and with the housing stock identified as one of the primary generators of carbon emissions, the “Future Homes and Building Standard” was conceived, stipulating new targets and requirements regarding the energy efficiency and green credentials of new build homes.

The “Future Homes and Building Standard” is set to come into effect in 2025. As homes become more energy-efficient and more air-tight, ventilation and air circulation increase in importance with a view to preventing air becoming stale and excessive temperatures causing the proliferation of pathogens and allergens. In addressing the problem of carbon emissions and heat loss as a result of dissipation, we have in effect created a new problem in the need for improved and more effective ventilation solutions. This has brought with it a variety of changes to existing building regulations, and the introduction of some new ones.

Check out our previous blog entries for information on ventilating the homes of the future and tips on ventilation design.

Building Regulations: changes and new additions

With adequate ventilation having been identified as key to tackling overheating building regulations, amendments to Approved Document F, which stipulates provisions for ventilation within buildings, are of central importance in tackling overheating and improving indoor air quality.

However, on 15 December 2021, the government went one step further in introducing the new Part O Building Regulation, which specifically deals with the issue of overheating’s building regulations in dwellings and domestic-style commercial buildings such as care homes and student accommodation. The new regulations came into force in June 2022 and require that measures be taken in dwellings and residential properties to mitigate overheating by:

limiting unwanted solar gains in summer
providing an adequate means to remove heat from the indoor environment

Overheating building regulations: how to comply and demonstrate compliance

The overheating building regulations also stipulate requirements with regard to ensuring and demonstrating compliance. Suggested methods by which to limit solar gains and remove excess heat are outlined in the table below:

Limiting solar gains	Removing excess heat
Installation of shutters, external blinds, or overhangs	Opening windows
Adaptation of glazing design, e.g., avoidance of south-facing windows	Installing vents
Building design, e.g., incorporation of balconies	Installation of a mechanical ventilation system
Provision of shade by means of surrounding buildings or landscaping	Installation of a mechanical cooling system (air conditioning)*

* Section 2.11 stipulates that “The building should be constructed to meet requirement O1 using passive means as far as reasonably practical. It should be demonstrated to the building control body that all passive means of limiting unwanted solar gains and removing excess heat have been used first before adopting mechanical cooling.”

Performing an overheating assessment: routes to compliance

Approved Document O identifies two routes by which to demonstrate compliance with overheating building regulations; a simplified method and a method that applies thermal dynamic modelling.

The simplified method involves limiting glazing on the south, west, and east façades of the building, ensuring a sufficient quantity of opening windows. The drawback for developers in this instance is that the simplified method requires the submission of details regarding the glazed and opening areas of every single window within a dwelling. Approved document O specifies limit levels in this regard, with a distinction drawn between high-risk urban areas, and moderate-risk locations.

The thermal dynamic modelling route involves the creation of a model of the dwelling using thermal dynamic modelling software. In order to demonstrate compliance, the model will need to show that the internal temperature within a space does not exceed a specified temperature for a certain number of hours. The benefit here is that it provides greater flexibility in the design of a compliant dwelling, data can be easily submitted to the relevant control bodies, and the majority of developers will already be familiar with such software. This involves the use of two Technical Methodologies from CIBSE, TM52 and TM59 which outline the above in more depth. These are often used during the initial phase of the project and passed onto the planning and building control officers.

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Overheating Building Regulations in the UK

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