Richard Poole from Siegenia addresses how and why housing managers should meet the new air exchange targets
The updated new building regulation Approved Document F covering ventilation came into force on 15th June 2022. Part F concerns construction projects that are new or result in the change of use of a dwelling or all other buildings in England. It therefore sets the standards for the ventilation of both new and existing buildings and needs to be considered by any housing management companies considering undertaking upgrades to
their stock.
Why is Part F changing?
The outgoing Part F has been in place since 2010, but over the years key issues have been identified and concerns have been voiced over the failure of homes complying. In 2020, guidance from Public Health England on selected volatile organic compounds (VOCs) indoors and World Health Organisation (WHO) recommendations for indoor pollutant levels meant Part F, as it stood, was out of date.
Part F is also very closely linked with Part L (conservation of fuel and power), as both are being improved to meet the Government’s Future Homes Standard. One way of improving energy efficiency is to reduce the heat loss through air permeability, thus building more airtight homes. However, an increased air tightness leads to reduced ventilation and, therefore, Part F requires updating to ensure that sufficient levels of ventilation are still provided.
Changes to Approved Document Part F
- Simplifying the approach for determining the ventilation rate and system design requirements for a dwelling
- Changing the way that ventilation systems are presented in the Approved Document to reflect common design practices and latest evidence relating to air quality in homes
- Introducing guidance to reduce the ingress of external air pollutants into the main body of the Approved Document
- Simplifying the structure and content of the guidance
Why the change now?
Ventilation remains an ongoing challenge not just for private developers and self-builders, but also for those of us undertaking any refurbishment works on properties. With increasing air tightness standards in the UK for new build homes and the focus on procuring the most energy efficient products, we end up creating nothing more than highly efficient sealed boxes. This may sound ideal (and from an energy conservation point of view it is) but without a properly considered holistic ventilation strategy, poor indoor air quality and issues of condensation and mould will ensue and become a recurrent problem for housing managers and landlords.
Why do homes require ventilation?
Ventilation specialists will generally quote a ‘maximum’ air tightness of 4-5m3/hm2 as a healthy rate for a naturally ventilated house. That is, ventilated only with extract fans, trickle vents and windows. Anything tighter and some form of forced ventilation will be required.
According to the Environmental Protection Agency, the levels of indoor air pollutants can be two to five times higher than outdoors. The primary function of a ventilation system is to reduce the moisture in the air. The average family of four produces about 15 litres of moisture each day from activities such as bathing, cooking, washing and breathing.
Ventilation also helps dilute the effects of carbon dioxide (CO2) released through breathing, smoking, cooking and burning fossil fuels. CO2 levels are measured in parts per million (ppm). Normal outdoor ambient air is regarded as 250-400ppm and safe levels between 400-1000ppm is typical of indoor spaces with good air exchange.
The traditional trickle vent solution
Trickle vents are considered under the topic of ‘background ventilation’ in the new approved document F, stating that these will be a legal requirement for the majority of window installations in England. The new legislation also clearly sets out the ventilation requirement of any habitable room and defines this by “equivalent area” (EA) measured in millimetres squared. For example, a host room that will have no openable windows once an extension or conservatory has been added will need 10,000 mm² EA for ventilation, while an existing bathroom will require trickle vents of 4,000 mm² EA.
Trickle vents are very effective at allowing the exchange of outdoor air with indoor air in the same way that an open window does but in a much more controlled way. Unfortunately, however, in the bid to seal up our homes to prevent heat loss they have often been omitted by the developer or later blocked up by the homeowner.
Alternative ventilation methods to consider
The new legislation allows several options (or work arounds) to further improve ventilation performance and/or energy conservation. Centralised whole-house heat recovery systems have been around for some time and have often been the go-to ventilation solution. However, the installation of these systems does require careful design and planning due to the spaghetti of ducting required to interconnect all rooms. For this reason, they are normally seen as too costly and disruptive for renovations and only considered for new build projects.
Decentralised whole-house heat recovery ventilation is less understood but offers some significant benefits over its centralised cousin, making it a real viable solution for refurbishment projects. As each unit is self-contained there is no need for a loft-mounted centrally managed ventilation device and the associated costly and time-consuming ducting. Once the wall opening is prepared, the installation of each ventilation unit is completed in less than one hour.
These single-room heat recovery units run continuously and automatically switch between air extract and supply in around minute intervals. When running in extract, warmed stale air from the room is extracted and heat is collected in the heat exchanger. The cycle then changes and the unit switches to air supply drawing in fresh air from outside and transferring the captured heat to the incoming clean air supply to raise the fresh air temperature before entering the room. Using heat recovery units as opposed to conventional fans or trickle vents reduces heat losses significantly, with some units, such as SiegeniaI’s Aerotube WRG, recovering as much as 90% of the heat. Single-room ventilation units also provide a constant supply of fresh air to help maintain a healthy home environment.
It is therefore sensible to consider decentralised systems as a credible alternative to both centralised systems and trickle vents, when looking to renovate your housing to meet ventilation standards.
Richard Poole is head of ventilation sales at Siegenia