Approved Document O is the section of the Building Regulations that addresses overheating risk in residential buildings. It was introduced to help ensure homes remain comfortable and safe during periods of hot weather.

Assessments are typically required for: New-build houses. Apartment developments. Student accommodation. Care homes. Residential institutions. Certain conversion projects that create new dwellings.

Several factors can contribute to overheating, including: Large areas of glazing. High solar exposure. Limited shading. Poor ventilation. Urban heat island effects. Highly insulated and airtight construction without adequate cooling strategies.

The Simplified Method follows a set of prescriptive criteria within Approved Document O and is generally suitable for straightforward developments. Dynamic Thermal Modelling is a more detailed computer simulation that predicts how temperatures within a building change throughout the year. It is typically used for larger, more complex or higher-risk developments where the Simplified Method cannot demonstrate compliance.

Yes. Overheating assessments are often most valuable when undertaken early in the design process. The results can inform decisions on glazing, shading, ventilation, façade design and building orientation before construction begins.

Yes. Ventilation is a key part of the assessment, and the ability to remove excess heat through openable windows or other ventilation strategies is an important consideration.

Buildings designed to minimise heat loss in winter can be more susceptible to overheating during summer if adequate mitigation measures are not incorporated. Overheating assessments help achieve the right balance between energy efficiency and occupant comfort.

Not necessarily. Approved Document O encourages passive measures such as shading, glazing selection and natural ventilation before relying on mechanical cooling. Many developments can achieve compliance without installing air conditioning.

Typical information includes: Architectural drawings. Floor plans and elevations. Window schedules. Façade and glazing specifications. Ventilation strategy. Site layout and orientation information. The level of detail required will depend on the assessment method being used.

Ideally during the early design stages of a project. Assessing overheating risk early allows mitigation measures to be incorporated efficiently and cost-effectively, reducing the likelihood of redesign later in the project.

Yes. Overheating assessments are often undertaken alongside daylight and sunlight studies, energy assessments, SAP calculations, SBEM calculations and wider building physics analysis to ensure the building performs effectively as a whole.