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Wednesday, May 25, 2022

Part O Signals Increase in Shading Needs, by Richard Webb.

The UK needs a huge increase in solar shading to mitigate the effects of climate change. That is the solution to rising temperatures mooted by the UK government in Part O of the Building Regulations, which comes into force on 15th June 2022.

This update to the regulations will change the way developers and specifiers tackle overheating in new-build residential dwellings, and existing housing and office stock will also need retrofitting to mitigate the impact of climate change. Here, Richard Webb, Specification Manager at Waverley, explains.

Richard Webb, Specification Manager, Waverley.

With the climate emergency high on every architect’s agenda, there has been a lot of talk focused on insulating our homes to make them more suitable for alternative energy sources and to reduce our heating costs. Not so much has been said about protecting our homes from the impact of rising air temperatures which threaten to increase the number of regions in which air conditioning may be required to make properties bearable in summer.

Part O of the Building Regulations is designed to address this as far as new builds are concerned.

The objective is to mitigate overheating by making reasonable provision to limit unwanted solar gains in summer and provide an adequate means to remove heat from the indoor environment. Part O stresses that “The building should be constructed to meet [the] requirement using passive means as far as reasonably practicable… Any mechanical cooling (air-conditioning) is expected to be used only where [the] requirement cannot be met.”

The new regulations stipulate the maximum glazed areas for residential buildings with and without cross-ventilation and that buildings in a high-risk location should provide shading for glazed areas between compass points north-east and north-west via the south. This shading should be provided by one of the following means:

  • External shutters with provision for ventilation
  • Glazing with a maximum g-value of 0.4 and a minimum light transmittance of 0.7
  • Overhangs with 50 degrees altitude cut-off on due south-facing façades only

But this is just for new structures. Insulate Britain has highlighted the leaky properties we already live in. This existing stock has also been the focus of a recent research project on solar gain, conducted by Guidehouse for ES.SO (the European Solar Shading Organisation).

ShadeTech external blinds are a fixture of many office buildings.

The investigation builds on a statement from the Intergovernmental Panel on Climate Change that, between now and 2050, the average number of days a year in which the continent of Europe requires air conditioning will rise by 30%. If the answer to hotter buildings is to add more air conditioning, hitting the net zero GHG emissions target by 2050, as required by the European Climate Law 2021, will be nigh on impossible.

Just like the UK’s Part O regulations, this research recommends that passive measures like external shading are the first line of defence. Keeping solar gain to a minimum is crucial to prevent greater use of costly, environmentally damaging air conditioning units.

The model created in the report estimates that dynamic solar shading can save up to 60% of electricity used for space cooling by 2050. Across Europe, this amounts to some 870 TWhel, roughly the total energy consumption of Spain in 2020.

If this massive retrofit (equivalent to 70% of all Europe’s buildings by 2050) is attempted, surely the cost and energy required to build and install the shading would be huge? The ES.SO report is clear. The total capital expenditure needed will be no greater than that involved in building and installing all the new air conditioning units that would otherwise be needed for people to comfortably use homes and offices.

Can this be achieved? Clearly, the UK is not likely to experience the same levels of impossible heat as more southern countries and many recently-built office developments have highly effective automated external shading incorporated into their design. That means help can be targeted at those densely-populated areas and those buildings where levels of solar gain are likely to be most extreme.

In the UK, we have tended to specify more internal shading, while our continental partners have adopted external blinds and shutters. It is time we caught up. External shading, especially the kind which operates automatically when conditions are right, is the answer.

The good news is the UK has a highly developed manufacturing capacity for solar shading. Our job, in the industry, is to make sure we maintain the expertise, the industrial capacity and train more installers so we can fulfil the demand which is sure to come. My message to UK architects is to research the many passive shading options available and be frank with their clients about what they might need in years to come. We have less than 30 years to bring this about.


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