CIBSE Technical Memorandum 59 - Overheating in Dwellings

CIBSE TM59 provides a standardised methodology for predicting overheating risk for residential building designs (new-build or major refurbishment) using Dynamic Thermal Analysis.

The Approved Document Part O introduces two ways to demonstrate compliance:

1. Simplified Method for limiting solar gains and providing a means of removing excess heat through window sizing or window design; or,

2. Dynamic Thermal Analysis also known as Dynamic Simulation Method (DSM).

CIBSE TM59 is an approved Dynamic Thermal Analysis approach that can be used to demonstrate compliance for Building regulations Part O.

About CIBSE TM59

The methodology provides a baseline for all domestic overheating risk assessments and also provides a set of profiles that represent reasonable usage patterns for a home suitable for evaluating overheating risk.

CIBSE TM59 is intended for use by designers in order to influence building design for the better. It could be used at the planning stage to assess risk, as well as at later stages of design.

Modelling Requirements

Dwellings are required to be be modelled as occupied for 24 hours from May to September with no differences between weekdays and weekend.

The weather file used for TM59 should be the CIBSE DSY1 (design summer year) file most appropriate for the site location for the 2020s, high emissions, 50% percentile scenario

CIBSE TM59 Compliance Criteria

TM59 Compliance is based on passing both of the following two criteria:

(a) For living rooms, kitchens and bedrooms: the number of hours during which the operative temperature is greater than or equal to one degree (K) during the period May to September inclusive shall not be more than 3 per cent of occupied hours;

(b) For bedrooms only: to guarantee comfort during the sleeping hours the operative temperature in the bedroom from 10 pm to 7 am shall not exceed 26 °C for more than 1% of annual hours. (Note: 1% of the annual hours between 22:00 and 07:00 for bedrooms is 32 hours, so 33 or more hours above 26 °C will be recorded as a fail).

Both (a) and (b) above must be passed for all relevant rooms.

How can we help you?

We can assist you with building regulations Part O compliance and any other overheating risk analyses requirements you may have. To discuss your needs, please contact us on:


11 Caithness Crescent
Manor Kingsway
Derby DE22 3XS


01332 492082


0788 6277 818