Air of authority: CIBSE’s guidance on indoor air quality

With the UK government coming under increasing pressure to tackle air pollution, Hywel Davies reviews the CIBSE guidance on building air quality

European air-quality standards require member states to undertake air-quality assessments and report the results annually. The EU Directive 2008/50/EC on Ambient Air Quality and Cleaner Air for Europe, and the Fourth Daughter Directive (2004/107/EC), are implemented through the Air Quality Standards Regulations 2010 and further legislation in the devolved administrations.

Monitoring has shown that much of the UK has a problem with pollution, and specifically with nitrogen oxide (NOx) emissions. The latest annual report published for 20151 shows that – out of 43 monitoring zones in the UK – just six met the limit for annual mean NOx levels. By far the worst case is London, but a number of other urban centres are also well above the limit.

As a result, the UK government has been under pressure to produce a plan to reduce NOx emissions to the limits set in the 2010 regulations. The latest version was published on 26 July2 to much media comment, and included the proposals to ban the sale of new diesel- and petrol-engine vehicles from 2040.

Out of 43 monitoring zones in the UK, just six met the limit for annual mean nitrogen dioxide levels

In the meantime, there has been a flurry of activity in the building services press over standards for indoor air quality (IAQ). The Greater London Authority is consulting on the planning framework for the London Plan, and there have been calls for the creation of an air-quality standard. Given the pollution levels in London, delivering acceptable and healthy air quality inside a building is more of a challenge than it is in Brighton, Blackpool or the Borders – all of which meet the legal limits.

But there is considerable CIBSE guidance available for services engineers delivering projects in urban areas with higher levels of pollution. IAQ is addressed in detail in CIBSE technical guidance, with principal references being Guides A and B, and further guidance in AM10 Natural Ventilation, TM57 Schools, TM21 – on minimising pollution at air intakes – and KS17, which offers an overview of the topic. The new edition of TM40, on health in buildings, will also address air-quality issues.

Guide A Chapter 0 gives the background to health and indoor air quality in building design, while chapter 1 sets out the primary criteria and associated indicative air-supply rates.

Chapter 4 includes the basic ventilation rates, in litres per second per person, for the BS EN 13779 IAQ categories, where IDA 1 is the highest indoor air quality and IDA 4 the lowest. The chapter also recommends ventilation rates for specific spaces in dwellings and offices, and gives references for spaces such as call centres, clean rooms and prison cells.

In addition, it introduces the classic ‘pollution concentration equation’ for assessing the potential of a space to control levels of transient pollutants, with an example of occupant CO2 emissions and polluted outdoor air.

Chapter 8 provides the main commentary on IAQ, with typically required fresh-air supply rates for acceptable CO2 levels. There is guidance on indoor pollutants and their health – and sensory – effects, and links to relevant occupational exposure limits. Table 8.3 shows the influence of poor system practices, such as unclean ductwork, on occupant respiratory symptoms.

The chapter also considers the importance and impact of outdoor air on IAQ, the typical relative pollution of the ‘fresh’ air we use, and means of moderating the impact of poor outdoor air quality on IAQ. There is a brief discussion of the impact of IAQ on sickness and productivity – a topic that is coming to the fore with the growing interest in wellbeing in buildings.

There is now a page on the CIBSE website3 that offers a detailed review of all the published, peer-reviewed CIBSE guidance on indoor air quality, as well as recent CIBSE Journal articles. The page is an essential read for anyone working on the topic.

While engineers have to design for the prevailing conditions, better outdoor air quality and reduced levels of pollutants will improve the quality of the ‘fresh’ air we use to ventilate our buildings. It will also reduce the need for measures to remove or control outdoor pollution inside buildings.

For these reasons, it is essential that government takes serious steps to control pollution and meet the current legal standards. In the meantime, Journal readers should make full use of the available guidance and standards for indoor air quality.


  1. Air Pollution in the UK 2015, September 2015, Department for Environment, Food and Rural Affairs (Defra)
  2. UK plan for tackling roadside nitrogen dioxide concentrations, July 2017, Defra and the Department for Transport
  3. Indoor air quality – an outline of CIBSE information, May 2017
  • Dr Hywel Davies is technical director at CIBSE