When undertaking energy-efficient retrofit projects, it’s crucial to consider whole-house ventilation to avoid moisture build-up and other problems.
In this blog post, Phil Partridge, Retrofit Designer at VOR, provides an overview of the different types of ventilation available. He explains the minimum standards needed to comply with Part F regulations and highlights the importance of considering the existing ventilation when making fabric improvements to existing dwellings.
Ventilation considerations for EEM retrofits for older properties
Fabric improvements to existing dwellings should consider the existing ventilation strategy and make improvements where necessary. Often, older/traditional properties rely on infiltration ventilation. However, when installing EEMs, these ventilation routes are often removed or significantly reduced (ventilation floor void, windows and doors etc.). It is essential that whole-house ventilation is considered to avoid moisture build-up, damp and mould.
Phil Partridge, Retrofit Designer at VOR, says, ‘Fabric improvements to existing dwellings should consider the existing ventilation strategy and make improvements where necessary. Often, older/traditional properties rely on infiltration ventilation. However, when installing EEMs, these ventilation routes are often removed or significantly reduced (eaves ventilation, underfloor ventilation, windows and doors etc). It is essential that whole-house ventilation is considered to avoid moisture build-up, damp and mould.
Background ventilation
The most popular background vents are trickle vents found in the heads of windows. Wall vents are also common in older properties. The mechanical ventilation strategy adopted will impact the background ventilation requirement (IEW typically requires more background ventilation).
Door undercuts enable air to flow around the property between habitable/wet rooms when all internal doors are closed. 7600 mm2 free area is required, typically a 10mm gap to the bottom of a 762 mm (typical domestic 2’6″ door), although it will be more for narrower doors and less for wider doors.
Mechanical ventilation
Minimum whole-house ventilation rates must be achieved to satisfy Part F – either based on the number of bedrooms, or 0.3 x total floor area, whichever is greater. All mechanical extract fans combined must reach this minimum.
- IEV (intermittent extract ventilation) – widely used to extract moist air from wet rooms on demand (kitchens/bathrooms/utility rooms/sanitary accommodation*). Under PAS2035, the use of IEV results in post-installation air testing for compliance.
- dMEV (decentralised mechanical extract ventilation) – Favoured strategy as it omits the requirement for air testing (subject to risk pathway). Units are small and unobtrusive and can be located in wetrooms where required to achieve the minimum ventilation rates per room type to comply with Part F and to achieve the minimum whole-house ventilation rate.
Purge ventilation
Habitable rooms should have adequate purge ventilation (openable windows) to achieve the minimum standards in Part F.
Combustion appliances
Wood-burning stoves are becoming increasingly popular. However, the ventilation requirements are often overlooked. Most domestic stoves have a rated output of less than 5kW, typically requiring no dedicated ventilation to the appliance. However, existing background ventilation should comply with the minimum standards in Part F. Where changes to background ventilation are proposed or may have otherwise been removed/sealed, combustion appliance ventilation must be considered and re-instated.
