Overheating Risk Assessment Methods

Approved Document O was released in December 2021 and sets out two methods for calculating and assessing overheating in domestic properties. The main requirements are to demonstrate the project limit unwanted solar gains, and provides an adequate means to remove heat from indoor environment.

Compliance is demonstrated by either of the following methods:

1. Simplified Method

Which categorizes buildings according to location and cross ventilation applicability. For this method compliance is based on maximum glazing areas; minimum opening areas.

2. Dynamic Thermal Modelling

This is in accordance with the CIBSE TM59 methodology but with additional limitations.

Overheating Mitigation Strategy

The following section details the modeling strategy and possible design guidelines to prevent overheating, taking into consideration the projected climate scenario for the year 2050. It also highlights essential design components that may be integrated into the detailed design phase of the planned development to minimize the risk of overheating.

Mitigation options following the cooling hierarchy approach.
Cooling hierarchy	Design element		Discussion
Reduce the heat entering the building	External shadings	External shutters	Choose the right shading for your window based on its size and orientation. Vertical shades work best for windows on the West and East sides because they block out diagonal sunlight. For windows facing South, horizontal shades are effective.
		External blinds (automatically controlled based on indoor temperatures or solar radiation)
		Awnings
	Window size		When determining the size of the windows, it is important to take into account how much sunlight they will receive (especially if they face south) as well as the amount of airflow needed for the specific purpose of the room.
	External reveals		Deep external reveals are an effective way to decrease the amount of solar radiation. When these features are properly integrated into the building's façade, they give the structure its unique identity.
Managing internal heat	Ceiling height		Increasing the internal floor-to-ceiling heights to be greater than 2.8 meters can contribute to enhancing the stratification of air movement.
	Exposed thermal mass		Utilizing thermal mass materials that are exposed in certain architectural elements like internal walls, floors, or ceilings can effectively mitigate rapid temperature increases, although proper ventilation is essential during nighttime hours.
Provide Natural Ventilation	Fully openable windows		Window sill height should be designed to ensure windows can safely open (B.R Part K Guarding heights).
Provide Natural Ventilation and Noise Mitigation	Passive measures	Plenum windows	Plenum windows enable the utilization of operable windows, thereby minimizing the impact of external noise. These windows have the potential to achieve a noise reduction of up to 11dB, as stated in the AVO Guide v1.1 2020.
		Acoustically treated ventilated louvres	Conventional acoustic louvres, when combined with a fan, have the ability to improve air circulation within a given area, all the while reducing external noise. These louvres are capable of achieving a noise reduction of up to 11dB (AVO Guide v1.1 2020).
Provide Mechanical Ventilation	Tempered fresh air MVHR units (peak looping)		During the summer months, these MVHR units have the capability to supply a certain quantity of fresh air at a reduced temperature, which is known as free cooling. This feature aids in promoting natural ventilation and helps in minimizing the potential of overheating.
Provide Active cooling	Active cooling		Active cooling should only be employed as a final option once all passive measures from the 'cooling hierarchy' have been thoroughly investigated.

How SEES can Help?

SEES has extensive experience conducting overheating assessments for various building types including schools, offices, and residences. Our expertise in Dynamic Simulation Modelling allows us to efficiently analyse different building designs and compare their overheating outcomes.

Whether you require an overheating assessment to comply with Approved Document Part O, BB 101 2018, earn BREEAM credits, or fulfil a London Plan Energy Assessment, feel free to reach out to us for assistance.