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Achieving good indoor air qualityApril 2006

From April 6th 2006, new Building Regulations will be enforced for ventilation (Part F) and conservation of fuel and power (Part L). The Approved Documents that support these regulations are:

  • Approved Document F: Means of Ventilation
  • Approved Document L1A: Conservation of fuel and power in new dwellings
  • Approved Document L1B: Conservation of fuel and power in existing dwellings
  • Approved Document L2A: Conservation of fuel and power in new buildings other than dwellings
  • Approved Document L2B: Conservation of fuel and power in existing buildings other than dwellings

These can be downloaded for free from the ODPM website.

The main thinking behind these changes is to reduce the energy consumption of buildings while ensuring sufficient ventilation is provided. Approved Document F is all about ensuring healthy indoor environments by reducing the levels of pollutants and mould growth, whereas the Part L Approved Documents are all about reducing energy consumption.

An overview of these two documents follows.

Approved Document F

For dwellings and offices, Approved Document F 2006 gives three ways of complying with the new regulations:

1. Specified Ventilation Rates

This is a performance-based method based on specified supply and extract rates for different rooms. A fresh air supply rate of 10 l/s/person to office areas is specified. The 2002 Approved Document specified a rate of 8 l/s/person, but many designers have been specifying higher fresh air ventilation rates for some time.

2. System Guidance

This is a prescriptive method that gives guidance for natural and mechanical ventilation systems. Either way, similar ventilation rates apply as for the performance-based method outlined above. Some of this guidance is contained within the Approved Document, for example on controls and locations of ventilators. Second tier documents are relied on for further guidance, including:

  • CIBSE AM13: Mixed Mode Ventilation
  • CIBSE AM10: Natural Ventilation
  • CIBSE Guides A and B2

3. Performance Criteria

This is also a performance-based method. It details limits for pollutants such as Nitrogen dioxide, Carbon monoxide and Volatile Organic Compounds. There is little guidance on how these criteria can be met but all of them can be measured in some way. The measured levels of the pollutants listed above can be compared against the Workplace Exposure Limits (WEL) detailed in EH40 2005 produced by the HSE. These parameters are all key indicators of air quality.

Approved Documents L1A, L1B, L2A and L2B

A brief overview of the changes to the Part L Approved Documents is as follows:

  • Airtightness testing is now mandatory for a sample of new dwellings in a development, and all new non-dwellings. Tests must be carried out by approved competent testers.
  • Annual CO2 emissions must be predicted using approved calculation methods. These calculations take into account the measured airtightness, and must be carried out by registered competent persons.
  • Predicted emissions must meet a target, which is 20 to 28% better than the emissions fro a building that passed the 2002 regulations.
  • Dedicated Approved Documents have been produced for work in existing buildings, outlining reasonable provision for a variety of situations.
  • When extension to large non-domestic buildings are built, improvements have to be made to the energy efficiency of the existing building.


As airtightness testing will no longer be optional, all envelope elements must be designed for airtightness, and construction quality must match the designer's specification.

Achieving good Indoor Air Quality (IAQ) is an important issue. Office IAQ is particularly important as the workforce is a company's biggest asset and keeping them comfortable in their work environment is beneficial to all concerned. Improved airtightness means that designers can no longer rely on "accidental ventilation" to achieve good IAQ. Building ventilation rates can only be accurately predicted if the airtightness of the building envelope is known.

Leaky buildings lose more conditioned air due to infiltration and so require more energy to maintain the internal environment. Improved airtightness should result in reduced CO2 emissions from buildings.

Multidisciplinary Teams

The design of all building services systems and also the building envelope has an impact on CO2 emissions, so everybody involved in the design needs to be designing with energy efficiency in mind. The tightened targets give the message that energy efficiency can no longer be an afterthought, and needs to be considered at every step. A multidisciplinary team needs to be assembled at an early stage in the design process and CO2 emissions calculations also need to be carried out from the outset.

For more information on indoor air quality contact MicroClimate at BSRIA:

Tel: +44 (0) 1344 465600
or email


Construction compliance

Stress-free compliance with Building Regulations, including airtightness, sound insultation and ventilation