Overheating Criteria
CIBSE TM59 is based on CIBSE TM52 (2013) and CIBSE Guide A (2015) and provides a standardised approach to assessing overheating in residential spaces.
The three overheating criteria specified in TM52 are:
In a TM59 assessment:
TM52 provides definitions for different building categories as shown in the table below. For the purposes of a TM59 assessment, Category II is the default type for residential buildings excluding care homes and accommodation for vulnerable residents.
CIBSE TM59 is based on CIBSE TM52 (2013) and CIBSE Guide A (2015) and provides a standardised approach to assessing overheating in residential spaces.
The three overheating criteria specified in TM52 are:
- Criterion 1: This is a limit on the number of hours the operative temperature is above the upper limit of the comfort temperature. The hours of exceedance (∆T ≥ 1K) shall not be more than 3% of occupied periods during the period May-September.
- Criterion 2: Daily weighted exceedance. This is a limit on the degree of overheating in any given one day of the simulation period. It must be less than or equal to 6.
- Criterion 3: Absolute upper limit. This is an absolute temperature limit above the upper comfort temperature, beyond which normal adaptive actions will be insufficient to prevent discomfort. The value shall not exceed 4K.
In a TM59 assessment:
- For living rooms, kitchens and bedrooms, CIBSE TM52 criterion 1 must be passed.
- For bedrooms only, the operative temperature from 10pm to 7am 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).
- For homes that are predominantly mechanically ventilated, all occupied rooms should not exceed an operative temperature of 26 ̊C for more than 3% of the annual occupied annual hours (CIBSE Guide A (2015a)).
- The overheating test for corridors should be based on the number of annual hours for which an operative temperature of 28 °C is exceeded. Whilst there is no mandatory target, if an operative temperature of 28 °C is exceeded for more than 3% of total annual hours, this should be flagged as a significant risk within the report.
TM52 provides definitions for different building categories as shown in the table below. For the purposes of a TM59 assessment, Category II is the default type for residential buildings excluding care homes and accommodation for vulnerable residents.
