Advice: Addressing overheating risk in new housing

Home design needs to take account of the risks of overheating as climate change means hotter summers and insulation levels have been maximised, finds Ben Kochan.

PRP's Park Heights in south London has shading and deep-set windows to reduce overheating risk (PIC PRP)
PRP's Park Heights in south London has shading and deep-set windows to reduce overheating risk (PIC PRP)

The design of new housing developments has up to now focused on maximising insulation to minimise heating needs, but new homes are now at risk of overheating in the summer. Professor Kevin Lomas at Loughborough University’s architecture department says these problems have been exacerbated by climate change, which will bring more hot summers like this year’s. "We now need to design homes like those in the south of France," he adds.

Issues of overheating need to be considered from the initial design concepts for a development and then it needs to be followed through in the detail, says Marielle Assue, associate at architect Studio Partington. And building occupiers have to understand how to manage their space to maximise ventilation, she adds.

Here are five points to consider to address the risks of overheating in new housing development

1. Require outline schemes to be assessed for risks of overheating

Planning authorities need to require schemes to be assessed in terms of their overheating risk, says Assue. She points to the methodology developed by the Chartered Institution of Building Services Engineers in its memorandum TM59, which includes the percentage of hours at night when a target temperature should not be exceeded. Assue points out that the new draft London Plan would require its application on all schemes. Other local plans should require it, she says. 

Lomas says that overheating is likely to be considered in the next revision of the Building Regulations.

2. Assess different dwelling types

Overheating can be reduced with the right site layout, which maximizes opportunities for ventilation, says Assue, but she points out that trade-offs are inevitable. "Ensuring that windows can be opened is important, but there are issues of noise and pollution on many urban sites." There are also concerns about security, particularly on ground floor flats, which deter residents from opening their windows.

A systematic assessment of overheating risks is required of all the different dwelling types in a scheme, says Marylis Ramos, associate director at architect PRP. "Once the risks have been identified, the designs can be tweaked and mitigation measures developed," she says.

High rise blocks of flats are prone to overheating, says Tom Dollard, head of sustainable design at architect Pollard Thomas Edwards. Flats with a single aspect are particularly problematic because it is difficult to get a through flow of air, he adds. 

Internally generated heat also needs to be taken into account, says Dollard. Community heating systems circulate hot water round the blocks throughout the day and night, he explains.

3. Reduce glazing

The amount of glazing and its design needs to be managed. Architects like floor to ceiling windows, but these are a major cause of solar gain and overheating, says Ramos. On many of PRP’s high density schemes, like the one at Park Heights in south London, the windows are sunk into the façade, which reduces solar gain. "The downside of this approach is that the daylight getting into the home is reduced," she points out.

There are alternative approaches to providing ventilation without glazing, explains Assue. Non-glass opening louvred panels provide ventilation without allowing heat into the dwelling, she points out.

Windows can be designed to encourage airflow says Ramos. She points to the benefits of rooflights, which open to allow a through-draught. On PRP’s scheme at the North West Bicester ecotown ‘inside-outside’ rooms are being considered on the side of some of the houses. "These glazed sunrooms store the heat that would otherwise have gone into the home," explains Ramos. Good insulation between the sunroom and the rest of the house is then important, she adds.

4. Consider shading

Shutters are standard on most homes in southern Europe, points out Rory Bergin, environment director at architect HTA.  We need to consider them on UK homes, he suggests. He points out that shading strategies need to take account of the building’s orientation. On east and west facing windows, the shades should be vertical, while on the south side they need to be horizontal.

Internal blinds are helpful, but the heat has already got into the home, points out Ramos.  Balconies are useful for providing shade for the homes below, she adds.

5. Add greenery

Schemes should include maximum greenery. There’s a lot of evidence that trees can help urban areas cool down at night, which then stops the build up of heat over the summer, HTA’s Bergin points out.

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