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“It’s gettin’ hot in herre”: 10 causes of overheating

July 2016

In 2002 it was US Rapper Nelly who predicted the 2003 European heat wave and first brought to light the issue of overheating in modern UK homes.  But should you have to “take off all your clothes” to get some relief or are there better ways to negate overheating as designers?

One developer at a recent conference I attended described the scale of the problem by discussing a new flat they had monitored which had internal temperatures of “26-33oC for 33% of the time in July”.  From all the feedback in the industry we know they are not alone. Having been part of the Innovate UK BPE Programme I’ve seen the case studies that prove it.  The problem is set to get worse as the impacts of a warming climate are felt (summer of 2016 excepted!).  It could be that we are reducing elderly death rates from the cold in the winter but increasing them through overheating in the summer.  This may sound extreme but unfortunately, I suspect that an overheating death that is directly attributable to thermal comfort of a home is inevitable.

What is the solution? A summer fuel payment so that the elderly can operate air conditioning?  I hope not, because this is a problem purely of our own making.

So, what are the main reasons for overheating in the UK domestic sector?  I’ve gone all “BuzzFeed” and outlined our top ten below (in no particular order):

Top 10 causes of overheating

  1. Single aspect – A developers dream to maximise density but a tenant’s nightmare. As a rule of thumb a single aspect room can naturally ventilate a room depth only twice the room height, whereas a dual aspect room can naturally ventilate a room depth 5 times the room height.  Natural ventilation is unlikely to ever be sufficient in single aspect apartments.
  1. Floor to ceiling glazing – The high-tech obsession with large glazed expanses generates significant internal solar gain for limited functional purpose. Glazing below waist height provides limited view out, is difficult to shade and has limited benefit to internal daylight levels.
  1. Occupants – An unoccupied home with the windows shut and curtains or blinds open on a hot summer’s day is unlikely to be comfortable for some time when the occupants return. We must design for occupants by creating intuitive controls, providing a clear passive cooling strategy and completing a comprehensive handover.
  1. Security, acoustic or air pollution concerns – If people can’t leave windows open for risk of burglary, sleep deprivation or ill-health then overheating becomes a necessary evil. Ventilation strategies must incorporate a secure option that allows a space to be ventilated when unoccupied and doesn’t compromise contents insurance.  Air pollution is more difficult to address – where levels are very high apartments would require mechanical ventilation, in which case serious consideration should be given to whether dwellings are suitable for the site at all.
  1. Quantity and type of openings – A single bottom hung window with a tilt opening mechanism is not sufficient to ventilate a room in the summer. The free area and location of openings needs to be carefully considered when designing a natural ventilation strategy.  Dynamic simulation can help to optimise a strategy but in the end providing adjustable opening sizes is the ideal.  Giving people the ability to intuitively, tailor natural ventilation to specific conditions leads to high rates of occupant satisfaction.
  1. No shading strategy – If market trends command us to create greenhouses to live in then we must integrate a shading strategy. Dependent on a site’s location and a window’s orientation the shading can be external, integrated, internal or just another buildings shadow but it must be present and effective.
  1. MVHR – Typical domestic MVHR units provide background ventilation for fresh air purposes but do not tackle overheating unless sized appropriately. In fact, unless an effective summer bypass is in place MVHR will only make overheating worse.
  1. Heating services – insufficient insulation on pipework and valves, large thermal stores in small apartments and uninsulated heat interface units are all too common in new homes. This applies to both space heating and hot water services and is even more of an issue with communal heating.  Uncontrolled internal heat gains are often overlooked but have a significant impact on overheating.
  1. Internal communal corridors – internal corridors with no ventilation and communal heating services running through them (often poorly insulated) are the perfect storm of overheating risk. Heat builds up in the corridor from uninsulated pipework and is inevitably transferred to each adjoining dwelling. Designers should look to avoid internal communal corridors where possible or provide a ventilation strategy where they’re absolutely unavoidable.
  1. Urban heat island – night time temperatures in urban areas can be 5-6oC warmer than the surrounding countryside areas and therefore we must design for this and design to reduce it. Biodiverse roofs, integrated green corridors and restricting greenfield development over time will help to reduce the UHI.

Have we missed anything?  Add to the comments if you think we have. It’s not all doom and gloom though – we’ll be tackling our top 10 remedies for overheating with some examples of where this has been implemented in an upcoming post (now located here).  We know, overheating can be designed out; you only need to look at vernacular architecture from any Mediterranean nation to see how it’s done.

Author: Tom Kordel

IMG_2610

High-tech buildings from Tower Bridge

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