The brief reappearance of hot weather fits nicely with a return to the subject of overheating in modern homes. Following our 10 causes of overheating it’s time to address what we can do to improve the situation. As discussed in the previous post, overheating is a real problem in many modern homes and with a warming climate it is only going to get worse. Addressing overheating requires a considered and coordinated approach with input from the architect, services engineer and client to ensure that a suitable balance is achieved between negating overheating whilst allowing for daylight, heat gains and views and connectivity to the outside world.
The case studies provided below aren’t all XCO2 projects but in our view are examples of good design.
Top 10 remedies for overheating:
1. Considered Shading
Direct sunlight in summer can cause as much as 800W of heat to reach a building for every square meter of glazing. For most new homes, sunlight is likely to be the largest single heat gain in the living and bedroom areas, this critical factor should be addressed by (in order of preference):
- Reducing glazing size, although must be balanced with daylight levels
- External controllable shading
- Fixed external shading sized appropriately
- Solar controlled glass, although must be balance with lack of winter heat gains
- Internal shading
One site that deals with shading in an innovative way is DRMM’s Kings Cross Arthouse. Located on a narrow site with large exposed east and west facades, which are trickier to shade, the development uses sliding louvered screens that allow the residents full control of solar gain throughout the year.
2. Dual Aspects
Standard 29 of the latest London Plan Housing SPG requires developments to minimise the number of single aspect dwellings and to avoid single aspect dwellings that are north facing or exposed to high noise levels. Single aspect dwellings are particularly at risk from overheating due to the lack of ventilation options. Dual aspect flats benefit from being exposed to multiple wind directions and allow for cross ventilation. Ideally the aspects should be two opposing sides rather than to two sides of a corner in order to benefit most from cross ventilation options. Perhaps the need for more dual aspect flats will result in more long thin residential towers such as the Trellick Tower where all dwellings are dual aspect. A significant challenge for designers is how to integrate dual aspect whilst balancing the desires of developers to incorporate the high demands and good margins achieved by 1-bed flats as well as limit non-saleable circulation and core space.
3. Glazing Aspect Ratio
Current expectations of modern apartments dictates that floor to ceiling glazing is a must, but this approach creates problems with somewhat limited benefits. If instead, short and wide glazing is provided then it becomes easier to shade against high levels of solar gain and openings become better distributed in rooms allowing for improved ventilation. Such a strategy is demonstrated in our project with Foster Lomas in the Isle of Man where a large window wraps around a southern façade, allowing sweeping views out and limiting solar gain in.
4. Ventilated Corridors
With the rise of communal heat networks, overheating in shared spaces has become a significant concern due to heat losses from the networks building up in landlocked corridors. Heat in the core always radiates out to the extremities so we must address internal corridors to limit overheating in adjoining flats. Our first priority should be to minimise internal gains from heat networks through good design and installation (see the CIBSE Heat Networks: Code of Practice for a large step in the right direction). Once internal gains are minimised the risk of an overheating corridor could be fully designed out by integrating external corridors, the Isokon Building is an excellent example of this. Alternatively, internal corridors should adjoin or end at external walls and allow for natural ventilation via openable windows. Finally, as a last resort mechanical smoke extracts can be appropriately positioned to allow for purging of internal corridors when temperatures rise, however, this is best avoided as it just adds to the overall energy consumption.
5. Natural Ventilation
Natural ventilation is driven by wind and the buoyancy created by temperature difference, it is an excellent way of purging heat from a home. Ideally designers should look to integrate multiple natural ventilation options into a home to give occupants the ability to adapt to external conditions. If it is windy then multiple openings on different facades allow for good cross ventilation whereas if it is still, high and low level openings can generate a stack effect. Traditional sash windows are a good choice since they allow for plenty of options including a stack effect by moving both window panes to the centre. A central north facing rooflight is a great option for houses wanting to introduce a stack ventilation option. This was adopted in our Retrofit for Living house with Penoyre and Prasad. A central light well offered a stack ventilation route whilst also offering a solution for drying clothes internally and allowing daylight penetration into the centre of the house.
6. Secure Ventilation
A significant cause of unaccounted (in compliance modelling) heat build-up is the sealing of homes when unoccupied. This problem is exacerbated in high thermal mass building where heat is slow to dissipate once windows are reopened. In order to assuage security concerns designers should look to ventilation options that can be left unattended such as louvered openings or secure tilt windows. Such a solution is also demonstrated in the Retrofit for the Living house where insulated louvered panels were placed next to the windows allowing the tenant a secure purge ventilation solution.
7. Considered Services Design
Building services can have a major impact on overheating in modern homes, particularly but not exclusively when communal heating is present. Some key areas to watch for include:
- Designing out hot water storage in apartments where feasible
- Insulating hot water pipework
- Continuous insulation of a heating system including valves and heat interface units
- Lowest achievable circulation temperatures for communal heating systems
- Insulating intake and exhaust duct work on MVHR systems
- Ensuring MVHR has an effective summer bypass
8. Engaged Occupants and Intuitive Controls
Although clearly blameless for bad design or flawed installation, occupants can have a substantial impact on a home with a tendency to overheat. Shutting the blinds or curtains of windows in a direct path of the sun, closing windows when external temperatures are higher than internal and opening them when the conditions are reversed. To aid occupants, as designers we must provide intuitive controls, clear guidance and seasonal handover support. From window handles to MVHR operation panels and heating programmers it is imperative that controls are clear and concise and that we avoid the temptation to take control away from building users.
9. Overheating Modelling
We must assess the risk of overheating at the earliest design stages so that fundamental changes to façade designs and layouts can be integrated pre-planning. SAP Appendix P as a compliance tool is not up to the task. Dynamic simulation modelling (DSM) (e.g. CIBSE TM52) is far more appropriate at assessing overheating with care taken as follows:
- Assess overheating against a standard. This is easier said than done at the moment since most standards (e.g. CIBSE TM52) were setup for non-domestic buildings and have minimal guidance on homes. Susie Diamond (Inkling) and Anastasia Mylona’s (CIBSE) presentation does an excellent job at presenting these issues and calling for more industry guidance.
- Use a weather file that is closest to the site and suitable for overheating modelling such as CIBSE Design Summer Year or UKCP09 climate projections
- Model significant neighbouring buildings that may shadow the site
- Input internal gains (e.g. occupant density, plant and pipework, lighting, small power) that are suitable to the project and ideally bespoke to the occupants
- Repeat the modelling for any changes in the fenestration design or specification
10. Post Occupancy Evaluation
Overheating modelling is all well and good but the best feedback is from monitoring of internal comfort conditions and occupant satisfaction when a building is in-use. Learning from past studies is also a great way to discover what has been successful or unsuccessful previously
Have we missed anything? Add to the comments if you think we have.
Author: Tom Kordel