Thursday, 11 June 2015

Why are we still designing buildings for yesterday’s climate?

Homes and buildings constructed today are very likely to be still in use 50 or even 100 years from now. (My home is 118 years old). So it would be sensible to design them to handle the climate that we can expect then, with warmer and drier summers and more frequent heat waves. However our current building regulations are more concerned with keeping us warm in winter than keeping us cool in sweltering summers. Plus the calculations they stipulate are based on historic weather patterns that are already out of date[1]. Between 1965 and 2006 the summertime daily mean temperature in the South East increased by 1.8°C and the daily maximum temperature increased by 2.0°C [2]. We can expect another couple of degrees on top of that at least.
External louvres on the top window and the overhang on the bottom window give shade that helps keep this home cool.
Picture from openecohomes.org



Innovate UK has produced a report to encourage us to take climate change into account when designing new buildings[1]. The precise impacts of climate change are very uncertain so they suggest that we should design for adaptability. Their report is concerned mainly with commercial buildings where, as they point out, there is a strong business case for keeping people comfortable. Workers are much less productive when they are too hot. In the worst case, buildings that cannot be adapted to the changing climate risk becoming stranded assets. Some measures can be installed during the lifetime of a building - for example adding window shutters, secure vents for night time cooling, changing the cladding to be more reflective, upgrading the air conditioning. However, other features are pretty much fixed from the start, like ceiling heights and the direction the building faces. So they recommend that designers plan for the worst, starting with the fundamentals and then with phases of additional measures that can be applied when needed.

What does that mean for our homes? I don’t see developers selling a home with blueprints for hot weather adaption options to be added as and when. Overheating may not hit our purses in the same way that it does business but it does seriously impact our comfort and health. In fact, overheating in homes is more important than overheating in offices because we are only in the office for part of the day. When hot weather makes it difficult to sleep our health really suffers. Also, elderly people that are at home most of the day often have more difficulty keeping cool because their sweat response is reduced. In Northern France in 2003, three weeks of sweltering days and nights led to 15,000 extra deaths [3]. Most of those cases were in older homes especially poorly insulated attic flats. However, new buildings are not immune to overheating, especially since the buildings regulations were changed in 2006 to require higher standards of air tightness.

NHBC and Zero Carbon Hub have done some very good research about this problem [3]. Overheating happens when heat accumulates faster than it can be removed. Heat gains come from a variety of sources such as sunshine through windows, cooking, electrical equipment or poorly insulated water pipes and tanks. For heat removal in this country we almost always use natural ventilation, though this only works if it is cooler outside than in. One of the NHBC case studies was a south west facing ground floor flat. On a hot sunny day the pavement outside reached 46°C and flagstones on the window cills hit 57°C. As you can imagine, this warmed up the air as well and it was only 2°C cooler outside than in so opening the windows was not much help. This case was extreme but the urban heat island effect can raise temperatures by 2-3°C over large areas of a city.

In Cambridge, considering temperatures in July over the last four years, there were 22 days where the temperature was 26°C or more for at least 4 hours of the day and 4 days when it was 26°C for at least 8 hours [4]. In warm weather like this the best thing to do is to close the windows and draw the curtains too, to try to keep the heat out.

Opening windows during the day may be counter productive but you should still be OK provided that the nights are cool, and you can ventilate thoroughly overnight, and the building has enough thermal mass that it takes a long time to warm up again. However, firstly nights are not always cool enough (in Cambridge, last July there were two nights when the temperature never went below 18°C [4]). Even when they are, you need a lot of ventilation, not just trickle vents or background levels from MVHR. You really need to be able to open windows wide on two sides of the building to get a through draught. In the flat I mentioned earlier it was not possible to leave the windows open at night because of noise (they were near a main road) and lack of security. In any case, the flat only had windows on one side so there would be no cross ventilation. These issues are common, especially in cities where you can't even leave upper windows open when the home is empty in case of burglars. Also, upper windows often have restrictors on to prevent them opening more than a little bit as a safety measure. There is some justification for this as thousands of children are injured each year in the UK from falling out of windows [3]. However, a little 50mm gap isn’t enough to get effective night time cooling.

So, we need to think a bit more out of the box. Keeping buildings cool is not rocket science and other countries manage it much better than we do. Simple measures can make a big different such as:
  • External shutters, louvres or overhangs to reduce solar gain through windows. Closing curtains helps a bit but external shutters are much better.
  • Shade and greenery to reduce the heat island effect, especially deciduous trees.
  • Lagging hot water pipes to prevent unwanted heat gain. Community heating systems are a particular problem because whereas the pipework between homes is always well lagged, that within each home is not, and they are hot 24 hours a day.
  • Whitewash or other reflective coatings on walls and roofs.
  • Secure grilles on windows to allow safe ventilation at any time, especially night time.
  • Roof level vents to maximise natural ventilation through the chimney effect.
  • Use fans to create air movement which makes sweating more effective. The US DOE reckons ceiling fans can give you cooling equivalent to about 4°F (2.4°C) [5]. But ceiling fans need high ceilings; standing fans tend to have a more local effect. Of course all fans use power (typically 40-80W) which adds to the heat gains so you need to use them in combination with ventilation.
Again, some of these measures can be installed later but this is much more expensive than putting them in at the start. We will certainly have to retrofit these features into many older buildings but let’s not make more work and cost for ourselves by omitting them from new ones too. The only people that will benefit will be air conditioning salesmen.

The best way to achieve this is to update the building regulations. They should require adequate shading and ventilation for the sort of weather we expect to have by 2050 - well within the lifetime of any new homes being built now. In the current market there is no pressure on developers to build homes that are comfortable to live in because they will sell them easily regardless. There simply aren’t enough homes being built to give buyers a choice. Where the market fails, regulation is the only answer.

[1] The business case for adapting buildings to climate change: niche or mainstream? (Innovate UK). 2015
[2] The climate of the UK and recent trends (UK Climate Projections, MET Office Hadley Centre) 2008
[3] Overheating in new homes: A review of the evidence (NHBC Foundation/Zero Carbon Hub) 2012
[4] Data from University of Cambridge Digital Technology Group
[5] Cooling your home with fans and ventilation (www.nrel.gov)

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