The Big Freeze appears set to continue! Winter is surely struggling its way towards spring! Now really is a good time for designers and planners to think of summer and the risks associated with overheating in buildings.
Summer Overheating Risks – The Drivers
Many scientists and meteorologists predict that there will be an increase in extreme weather events. These events could include prolonged heat waves even in the UK! 2017 was the second hottest year on record according to NASA data. In England 2003, there were over 2,000 excess deaths over the 10 day heatwave period which lasted from 4 – 13 August 2003, compared to the previous five years over the same period. Met Office – Heatwave Advice.
These events if combined with the build-up of heat in older buildings, or even modern air-tight buildings are likely to lead to an increased risk of overheating.
The UK government considers that such events are likely to present a risk to health. This risk is likely to be more sever to those susceptible including the very young, infirmed or elderly.
National Planning Policy & Regulation
This risk is countered through various means including Planning Policy with developers being required to prove consideration of overheating risk as part of a ‘Sustainability Statement’ and through Building Regulations Part L1 & L2 Criterion 3 deals with the issue of limiting the effects of Solar Gain.
These regulations are supported through various methods including BREEAM HEA04 or CfSH / HQM.
Guidance Documents Include:
- CIBSE TM52 The limits of Thermal Comfort: Avoiding Overheating in European Buildings
- BRE Guidance Document – Overheating in Dwellings
- CIBSE TM59 Design Methodology for the Assessment of Overheating Risk in Homes
- CIBSE A Guide
- BB101 Guidelines on ventilation, thermal comfort and indoor air quality in schools
Planning and Designing to Reduce Overheating
The Guidance listed above reveal many factors that may lead to an increased risk of summer overheating. Many of these should therefore be reviewed early in the design process to reduce the potential for overheating.
- Dwellings built within a dense urban area (heat island) with high night time temperatures have higher risk.
- Homes built close to noise sources such as busy roads or railways also have a high risk. Occupants as a result are not willing or able to open windows.
- Dwellings built in less secure districts also are at risk. Occupants may not therefore be willing to open windows.
- There may also be further risks for top floor flats due to increased solar gain through roof spaces.
- The use of shading from other buildings or even trees can help mitigate some of the risk.
Careful orientation of a dwelling is vital in dealing with summertime overheating risks. It is also key however to ensure that the supply of helpful solar gain is not curtailed during the heating season.
Dwellings with a high amount of unshielded windows facing south south/west tend to absorb higher levels of solar gain in the summer.
Design & Construction Factors
- Air tight dwellings will have a reduced natural or passive means for purging heat gains.
- Summer heat can also be absorbed and transmitted throughout a dwelling as a result of poor insulation.
- Dwellings with single aspects also provide no or little means of cross flow of air and purging of heat gain.
- Poor ventilation provision will likewise lead to a build up of heat without means of purging.
Energy Evaluation Services
Energy Evaluation Services (EES) recommend that designers and developers review the risk of overheating as an early part of the design process. EES can review designs and advise on the best way to address overheating while maximising the overall efficiency of the building. This can help reduce costs while ensuring the wellbeing of those using the space. Issues linked with location, orientation, design and build out can very often only be fully considered at these early stages. Indeed some BREEAM credits are only an option at the early phases of a design.
EES can assist through use of detailed models of proposed schemes and buildings. We use Dynamic Simulation Models (DSM) such as EDSL Tas. These models provide predictions based upon well proven guidance and targets to assess the level of risk. Our team can then provide further support to help mitigate the risk and review the design options.
EES assessments include reviews of:
- Passive Solar Design
- Thermal Mass
- Glazing design
- Fabric Design Review and Construction
For further help on Summer-time Sustainable Design please Contact Us . We help our clients make informed choices about the design options needed to secure planning consents, improve efficiency and reduce the overall development costs.