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Building Regulations Part F

All Systems

Due to the increasing complexity of the Regulations, ventilation strategies and system design must be considered at the earliest stages of building design.

The Building Regulations consider three ventilation types:

"Whole Building" (formerly referred to as “background”) ventilation to provide fresh air to dilute and disperse low levels of water vapour and other pollutants, usually by the provision of background ventilators or mechanical supply ventilation.

"Local extract" (formerly referred to as “extract”) ventilation in rooms where most water vapour or concentrated pollutants are released, usually by mechanical means such as extract fans.

"Purge" (formerly referred to as “rapid”) ventilation for the rapid dilution and removal of high concentrations of pollutants from occasional activities, usually by opening windows. The requirements for Purge ventilation are set out in Appendix B of Part F.

The performance rates for each of the “System” approaches set out in Part F are the minimum requirements needed to ensure that adequate air quality is provided for people indoors. The occupant’s health could be at risk if these ventilation rates are compromised.

The performance rates do not take account of summer overheating.

Most Systems may be manually or automatically controlled (with manual override).

For each System to be effective, air must be able to flow through the dwelling. The Regulations make provision for this via internal door undercuts to maintain a minimum gap of 10mm above the finished floor surface. This provides a 7600mm² permanent opening when a door is closed.

There are alternative methods to achieve compliance with Part F. The following explanations are simplified versions of the most common methods of interpreting the “Systems” approach set out in the provisions section of the Regulation.

Background ventilators are now measured in equivalent area (mm² EA) which is a better measure of performance but does not directly relate to the physical size of the opening through the ventilator.

System 1 - Intermittent extract fans and background ventilators

System 2 - Passive stack ventilation and background ventilators

System 3 - Continuous mechanical extract and background ventilators

System 4 - Continuous mechanical supply and extract with heat recovery

Download PDFs of Part F 2010 and the associated Domestic Ventilation Compliance Guide from www.planningportal.gov.uk.

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