Building Regulations update – Part L, O and S

 

In December 2021 the Government published the long-awaited update to Part L, confirming the energy, carbon and fabric standards which will be required once the Regulations are in force. Our summary document provides the key highlights and some commentary on the additional requirements set by the new Part O addressing overheating risk, and Part S setting requirements for electric vehicle charging.

Please contact AES to discuss the implications of these new standards for your development.

Overheating

Can new builds rise to the challenge of Climate Change?

The recent record-breaking heatwaves across the UK, following the previous heatwaves of 2018, have brought the risks of overheating into the public eye, even though it has been declared as a public issue by England’s Health Protection Agency since 2011.

The negative impacts of exposure to heat can be seen when daily temperatures surpass just 16-20⁰C (Committee on Climate Change: CCC). The social and economic impacts can range from, poor thermal comfort, reduced productivity and wellbeing, to fatalities. In 2017 the average number of heat related deaths per year was recorded at around 2,000 (CCC). At present an estimated 20% of the UK housing stock overheats in standard summer conditions, therefore as climate change takes hold and extreme weather conditions become the norm, more fatalities will inevitably occur, unless significant action is taken to reduce indoor overheating. The Environmental Audit Committee expect the average number of annual heat related mortalities to reach 7,000 by 2050. It is concerning that the number of heat related deaths is likely to triple in 31 years, and should be mitigated against as far as possible. Furthermore, it is estimated that circa 90% of UK hospital wards are prone to overheating (CCC). This puts already vulnerable groups at greater risk. This is a clear indicator of how the impacts of overheating will be felt more severely as the effects of climate change become more apparent.

Building Regulations, which must be met by all new build properties, require a certain level of fabric energy efficiency (i.e. the efficacy of building materials in retaining heat) to be achieved as well as low carbon emissions rates. These standards dictate well-insulated, air tight structures to maximise thermal performance. A well-insulated property will both prevent initial heat gain, and trap existing heat. It is therefore crucial to find a balance whereby heat gains from sunlight are utilised in the winter, and minimised in the summer. Accounting for the effect of thermal mass at design stage is also important.  Homes with high thermal mass can be very effective at combating overheating, however, when the materials do not have sufficient time to cool down during extended periods of hot weather, the heat builds up and it is difficult to achieve cooler temperatures at night. This highlights the difficulty in achieving the balance required to maintain comfortable indoor temperatures year-round, especially where overheating is not considered early on.

Low & High Thermal Mass

However, where overheating is considered early in the design process, there are many strategies and features that can be implemented in new buildings to combat overheating. Overheating can be reduced by:

  • Limiting glazing area on southern facades
  • Installing external shutters, this can enable the homeowner direct control of the amount of sunlight entering the property
  • Incorporation of cross ventilation. This allows air to flow through the building and alleviate high temperatures.
  • Utilising louvres which encourage ventilation whilst also blocking sunlight
  • Extending roofs to provide shade over windows
  • Green roofs and walls which work through insulation, shade, evapotranspirative cooling and the albedo effect
  • Wider landscape design to provide local shading
  • Window design to allow secure ventilation on the ground floor

While some of the features detailed in the list above can be retrofitted, most must be considered at design stage if they are to be cost effective. Air conditioning is a popular retrofit cooling solution and, while effective, it is problematic as it:

  • Is expensive to install and to run
  • Is energy intensive
  • Can worsen overheating for surrounding buildings by moving the warm indoor air outside
  • Can intensify the urban heat island effect
  • Uses Hydrofluorocarbons as the primary refrigerant, a greenhouse gas more potent than CO2

Air Conditioning Cycle

Air conditioning is therefore contributing to the problem that it is being installed to help solve. This is a vicious and counterproductive cycle, as shown in the diagram above, that could be stopped with more effective early design solutions to overheating.

It is estimated that 80% of the current UK housing stock will still be in use in 2050, and therefore retrofitting will be necessary for existing houses. This need not be the case for new builds. Installing measures to combat overheating is crucial to avoid health issues and additional cost to homeowners. By highlighting overheating risks through updated Building Regulations, the government could facilitate changes to the new build market. Many of the passive measures to reduce overheating discussed in this article can be tested in dynamic simulation software, and some local authorities have even made it part of their planning process to consider future weather data. It goes to show that the technology is available now to combat current and future overheating, and placing this risk at the forefront of design could provide future proofed homes for generations to come.

Overheating is an issue that is not going away, it will continue to grow over the coming decades. Think about how uncomfortable you felt in your home on the 25th July 2019, these temperatures will soon become the norm. Without change now, both us and the generations to come will have little respite from the overwhelming heat. New build developments must be designed now to cope with the climate of the future and not the climate of the past.

 AES Sustainability Consultants can assist designers with analysing the risks of overheating now and in the future. If this is something you would like to discuss further please contact Silvio Junges on silvio.junges@aessc.co.uk.

Written by Ella Cowen, Graduate Consultant