The ventilation of buildings

Generally the ventilation requirements of Approved Document F 2010 apply to the:

• The erection of new buildings
• The material alteration of an existing building
• The material change of use of a building

There are some exemptions including the erection or extension of buildings that are exempt under Regulation 9, Schedule 2.  This usually includes buildings unfrequented by people, small detached buildings, greenhouses, agricultural buildings, temporary and ancillary buildings.  Historic buildings are a special case and application of the requirements needs to be applied in a sympathetic manner having due regard to the sensitive nature of the fabric and its contents.
The purpose of ventilation is to replace ‘stale’ indoor air with ‘fresh’ outdoor air.  The process is essential to ensure a healthy internal environment by;

• Providing fresh air for breathing
• Removing air borne pollutants
• Controlling humidity
• Providing combustion air for fuel burning appliances

‘Purpose-provided’ ventilation is achieved by incorporating some or all of the following:

• Extract ventilation which may be natural, mechanical, continuous or intermittent and usually at a high rate
• Whole building ventilation which is continuous and usually at a low rate
• Purge ventilation which may be intermittent, manual, natural or mechanical usually at a high rate

Ventilation can be described as:

• Natural
• Mechanical
• Mixed-mode, or
• Hybrid

The strategy to be adopted in any particular building needs to be carefully considered and cannot be determined as a stand-alone solution.  In complex buildings ventilation strategies are normally designed by Building Services Engineers.  However, whatever the strategy it is important to consider the following:

• Conservation of fuel & power
• Condensation
• Temperature and humidity
• Controls
• The provision of combustion appliances
• Airborne substances
• Height, width, length, layout and design of the building
• Building fabric
• Fire safety
• Occupancy characteristics
• The spread of infection
• Uncontrolled infiltration of air or air leakage
• Air tightness of the building
• Testing and commissioning
• Installation and maintenance

Approved Document F 2010 provides detailed guidance on the various strategies that can be adopted for the ventilation of new dwellings including information on extract ventilation rates, whole building ventilation and purge ventilation.  There are generally four specific ventilation strategies described and they are;

1. Background ventilation - the provision of background ventilation, (such as ‘trickle vents) intermittent extract fans and purge ventilation.

2. Passive stack ventilation - the provision of free flowing ductwork to naturally vent the building, background ventilation and purge ventilation.

3. Continuous mechanical extraction - the provision of continuous extract ventilation, background ventilation and purge ventilation.

4. Continuous mechanical supply and extract with heat recovery - the provision of continuous whole building supply and extract ventilation with heat recovery and purge ventilation.

The use of natural or mechanical ventilation can be severely compromised when buildings incorporate basements, deep plan layouts, addition of extensions or the lack of through ventilation.  Additional guidance for dwellings is included in the Approved Document.
Guidance on the requirements for new buildings other than dwellings is also included in the Approved Document and includes specific guidance for offices.  However, more complex buildings will need to comply with other Approved Documents including CIBSE Guide B:2005.  The full list is provided in Table 6.3.
Additional guidance is provided in Appendix A on performance based ventilation.  This section should not be dismissed as it provides useful guidance on the background to the requirements and should be referred to when a variation to the guidelines is being considered.
The most important consideration is to provide an holistic and simple approach that enables the users of the building to control the ventilation of the building in a manner that is not only healthy but is also sustainable. The control of unwanted air leakage on new buildings is part of a planned control.  The same techniques associated with historic buildings may cause future problems especially with respect to surface and interstitial condensation.