Increasingly, overheating is becoming a significant issue in many buildings, with the situation expected to worsen as weather patterns change with the warming climate. Carrying out overheating analysis will assess the likelihood of your building becoming too hot in the summer months.
Your building/development may require overheating analysis to be carried out as part of an Energy Statement to satisfy local development plans.
A common example of this is The London Plan where buildings are
required to be analysed for overheating prior to construction. All of our overheating analysis is carried out on dynamic simulation software. This allows us to model the building in full detail before construction to determine overheating levels and to remedy any issues found with design/fabric changes.
What can cause overheating?
Factors that affect overheating risk are:
- Building location
- Geometry
- Fabric (including insulation levels and thermal mass)
- Levels of glazing (as well as orientation and glazing type)
- External shading (such as overhangs, louvres, blinds)
- Internal heat gains
- Ventilation
It should be noted that the overheating analysis carried out within SAP and SBEM calculations do not qualify as full overheating analysis as the calculation is very general. The performance of the building should not be assumed from a pass in these categories and a building should not be assumed to be low risk based on these results.
We carry out overheating analysis to the industry-standard definitions detailed below.
TM59
CIBSE Document TM59 offers a standardised approach to predicting overheating in homes. The approach is valid for new build as well as major refurbishments.
Criteria for naturally ventilated homes
Criteron 1
Hours of exceedance (living rooms, kitchens and bedrooms). The operative temperature cannot exceed the threshold comfort temperature (Tmax) by 1°C or more for over 3% of occupied hours between May-September. Tmax is a function of the outdoor running mean temperature.
Criteron 2
For bedrooms only, from 10pm to 7am the operative temperature shall not exceed 26°C for more than 1% of annual hours.
(both criteria must be passed to achieve compliance)
Criteria for mechanically ventilated homes
All occupied rooms should not exceed an operative temperature of 26°C for more than 3% of the annual occupied hours.
Communal Corridors
There is no mandatory target for communal corridors however it is advised that an operative temperature of 28°C is not exceeded for more than 3% of total annual hours. Should this occur the building will be marked as being at ‘significant risk.’
TM52
CIBSE Document TM52 uses a simple 28°C backstop and brings UK overheating analysis in line
with international standards. TM52 is based on ‘adaptive’ thermal comfort.
Criterion 1: Total Hours of Exceedance
The operative temperature cannot exceed the threshold comfort temperature (Tmax) by 1°C or more for over 3% of occupied hours between May-September.
Tmax is a function of the outdoor running mean temperature.
Criterion 2: Daily Weighted Exceedance
This is a limit on the degree of overheating in any given day of the simulation period. It must be ≤6 degree hours.
Criterion 3: Upper Limit Temperature
This criterion sets an absolute upper limit for the comfort temperature of a room.
The value should not exceed Tmax+4°C and is assessed between May and September.
BB101
Building Bulletin 101 provides an assessment of overheating and indoor air quality in schools.
Criterion 1: Total Hours of Exceedance
The number of occupied hours for which an adaptive thermal comfort threshold is exceeded.
Criterion 2: Daily Weighted Exceedance
The degree to which the operative temperature exceeds the adaptive thermal comfort threshold temperature.
Criterion 3: Upper Limit Temperature
The maximum temperature experienced at any occupied time.
BREEAM Hea 04
BREEAM 2014 Hea 04 ensures that thermal comfort levels are achieved through the design of the building. Hea 04 is subject to CIBSE guide A or a relevant industry standard. CIBSEA TM52 is used to provide overheating risk modelling while the Fanger Comfort Model can be used to assess thermal comfort in air conditioned buildings providing outputs of PMV (predicted mean vote) and PPD (predicted percentage dissatisfied), in line with BREEAM criteria.
For more information of BREEAM Hea 04 please see the BREEAM technical manual here.
Frequently Asked Questions
When building in London it is generally a requirement of The London Plan to have overheating analysis carried out. There is higher risk of overheating in London due to London’s heat island effect.
This depends on the design of your house however if there are elevations with significant levels of glazing then this would be highly recommended. An example would be a kitchen diner with large south facing bifold doors. The cost of the analysis is priceless compared to spending thousands on your forever home only to find that parts of it are unbearable in the summer heat. All of our models are run for the current climate as well a a future warmer scenario based on climate change predictions.
