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8.4.1.68.4.2.6 Ductwork
Ductwork to intermittent and continuously running mechanical extract ventilation systems shall ensure satisfactory performance and durability. Issues to be taken into account include:
- resistance to airflow
- installation of ductwork.
8.4.2.6.1 Resistance to airflow#
Ductwork systems should be designed to minimise the resistance to airflow and be formed from compatible components.
Rigid duct is preferable to flexible, but where flexible duct is used, it should be restricted in length to ensure that the airflow resistance does not prevent the designed ventilation rate from being achieved. Flexible duct should be installed:
- straight
- in accordance with the manufacturer’s recommendations.
Bends should generally be formed with proprietary rigid components. Where flexible duct is used to form bends on an intermittent extract system, they should be restricted to a maximum of:
- two for systems up to 30 L/s
- one for extract rates higher than 30 L/s.
8.4.2.6.2 Installation of ductwork#
Ductwork should be installed in a neat and workmanlike manner, be securely fixed, and have:
- adequate support throughout its length
- sealed mechanically fixed joints and connections.
Where ductwork passes through an external wall, it should be positioned to slope slightly outwards to prevent water entering the building. Clips and supports for ductwork should be spaced at equal distances and in accordance with the ductwork manufacturer’s recommendations. For rigid ductwork, they should not generally be more than 750mm apart.
Ductwork should not be in direct contact with other surfaces, such as plasterboard ceilings, that may transfer noise to the home.
It is not necessary to provide non-return shutters on extract fans or cooker hoods or their ducting unless specifically required by the manufacturer’s installation instructions.
Last updated: 2nd January 2024