PART O · Overheating
Part O building regulations explained
Part O deals with overheating in new residential buildings. It addresses unwanted summer heat and the ability to remove excess heat. A home can meet its winter energy requirements yet still become uncomfortably hot in summer.
Which buildings does it cover
The guidance applies to new residential buildings within its scope. Do not assume it automatically applies to every extension or refurbishment of an existing home.
The relevant building type and approval date need checking. Part O is a distinct requirement rather than a general label for all summer comfort advice.
How can compliance be assessed
The guidance provides a simplified route and a dynamic thermal modelling route. The appropriate method depends on the design and the limits of the chosen approach.
Window size, orientation, shading, location and the ability to remove heat can all affect the assessment. A single rule about the percentage of glazing does not explain every design.
Can occupants just open the windows
The design must consider whether its proposed measures are usable. Security, noise and protection from falls can affect how openings may be used, especially at night.
For example, a ground-floor bedroom beside a busy road may not be able to rely on the same opening arrangement as a sheltered upper-floor room.
Is air conditioning the first answer
Start by assessing heat gains and the available means of removing heat under the applicable approach. Do not assume a cooling unit excuses an otherwise unexamined design.
What should project owners ask
Ask which assessment route is used, what assumptions it makes and how the result changes if windows or shading are substituted. Retain the assessment and relevant operating information.
Coordinate Part O with Part F ventilation, Part L energy performance and Part K safety. The completed home needs a workable arrangement, not separate calculations based on incompatible assumptions.