Overheating Assessment for new-build dwellings in England
Please note that we currently only offer the Simplified Method of Overheating Assessment.
An Overheating Risk Assessment is a desk-based analysis of the potential for overheating of a building. Under the Approved Document O: Overheating, there are two methods of determining the overheating risk of a new building, a Simplified Method and the Dynamic Thermal Modelling method.
Simplified Method
Approved Document O details a Simplified method that can be used to provide a different way to assess the likelihood of overheating so that a more complex and expensive TM59 assessment doesn’t have to be done where it is deemed unnecessary. These focus on two areas, limiting solar gains and removing excess heat. The requirements to achieve compliance with these two areas differs depending on the location of the building and whether or not it has cross-ventilation. The simplified method looks at the area of glazing in proportion to the floor area, and prescribes a minimum free area (the geometric open area of a ventilation opening) that must be achieved. This is called a ‘Simplified Method’ for a reason, and is not an appropriate method of Overheating Risk Assessment in all buildings. Where this method is insufficient, Approved Document O prescribes the use of more complex modelling via the Dynamic Thermal Modelling method.
Dynamic Thermal Modelling: CIBSE TM59
CIBSE’s TM59: Design methodology for the assessment of overheating risk in homes is the backbone of the Dynamic Thermal Modelling method.
Dynamic simulation software must be used, and thus the cost to the developers is greater if this method is used. However, it will offer the designer additional design flexibility over the simplified method.
Simplified Method
Approved Document O details a Simplified method that can be used to provide a different way to assess the likelihood of overheating so that a more complex and expensive TM59 assessment doesn’t have to be done where it is deemed unnecessary. These focus on two areas, limiting solar gains and removing excess heat. The requirements to achieve compliance with these two areas differs depending on the location of the building and whether or not it has cross-ventilation. The simplified method looks at the area of glazing in proportion to the floor area, and prescribes a minimum free area (the geometric open area of a ventilation opening) that must be achieved. This is called a ‘Simplified Method’ for a reason, and is not an appropriate method of Overheating Risk Assessment in all buildings. Where this method is insufficient, Approved Document O prescribes the use of more complex modelling via the Dynamic Thermal Modelling method.
Dynamic Thermal Modelling: CIBSE TM59
CIBSE’s TM59: Design methodology for the assessment of overheating risk in homes is the backbone of the Dynamic Thermal Modelling method.
Dynamic simulation software must be used, and thus the cost to the developers is greater if this method is used. However, it will offer the designer additional design flexibility over the simplified method.
