8.4.2.3 System design
MEV systems shall be designed to minimise disturbance caused by noise. Issues to be taken into account include:
- location
- system
- compatibility
- performance
- control of condensation
- terminals.
8.4.2.3.1 Location#
MEV systems should be correctly located, including ancillary components, in accordance with the manufacturer’s recommendations.
The route of ductwork should take account of other building elements. Ductwork passing through structural elements should not adversely affect the structural or fire performance of the building. Where alterations to structural elements, such as I-joists, are required, this should only be carried out in accordance with the manufacturer’s recommendations or be designed by an engineer in accordance with Technical Requirement R5.
The fire requirements of the building should be in accordance with relevant Building Regulations and standards. Issues that should be taken into account include:
- suitable detailing of components passing through other elements of the building
- the location and type of dampers and firestops to be used
- the integrity of protected stairs and halls
- the integrity of walls and floors.
8.4.2.3.2 System#
MEV systems should be in accordance with relevant Building Regulations and installed to ensure that effective ventilation is provided without affecting health or creating unnecessary noise.
8.4.2.3.3 Compatibility#
MEV systems should ensure compatibility with other building elements and not adversely affect the performance of the building.
The MEV system should be designed as a complete package, taking into account the performance of all components and materials, to ensure compatibility and the performance requirements of the system.
Particular consideration should be given where components from different manufacturers are specified on the same system.
8.4.2.3.4 Performance#
The MEV system should be designed to provide satisfactory performance and be installed according to the design and manufacturer’s recommendations. Variations from the design should maintain the satisfactory performance of the system and be approved by the designer.
Issues that should be taken into account include:
- ventilation rates as set out in appropriate Building Regulations and standards
- fan capacity, accounting for airflow resistance of the system
- ensuring the even distribution of airflow, taking into account regulations and standards airflow resistance, including from bends and fittings
- airflow resistance should be calculated using figures for air valves and terminals determined in accordance with BS EN 13141-2 and data supplied by the duct manufacturer. Ductwork should be as direct as possible to reduce the number of bends.
Allowance should be made for air transfer within the home. Where gaps between the underside of internal doors and the floor finish are used for air transfer, the guidance in Chapter 9.1 ‘A consistent approach to finishes’ should be considered.
8.4.2.3.5 Control of condensation#
Where extract ductwork passes through unheated spaces, it should be continuously insulated to achieve a thermal resistance equivalent to a minimum of 25mm of insulating material with a thermal conductivity of 0.04W/(mK). This can be achieved by using:
- suitable pre-insulated ductwork, or
- a proprietary insulation system. See figure 3.
Alternatively, the ductwork can be fitted with a condensate trap that discharges to the outside or installing the duct to slope to the outside. See figure 4.
Figure 3: Ventilation control condensation - insulation
Figure 4: Ventilation control condensation - condense trap
8.4.2.3.6 Terminals#
Ventilation systems should terminate freely to open air.
The air flow resistance of terminals should not adversely affect the performance of the ventilation system. Airflow resistance of terminals can be obtained through testing in accordance with BS EN 13141-2. See figure 5.
Last updated: 2nd January 2024