Ruth MacEachern of EnviroVent looks at what the ventilation requirement changes for new homes mean for housebuilders in England and Wales, and how they can meet the challenge.
2022 was a year of significant change in the ventilation industry. Major updates to Approved Document L and F were introduced in a move towards the Future Homes and Building Standard, due in 2025. These standards will require all new build homes to be future-proofed with low carbon heating, effective ventilation and world-leading levels of energy efficiency. They also set out the ambitious target of reducing levels of carbon in new homes by 75% by 2025.
A major change to Approved Document F is the renaming of the ventilation methods. In the previous Building Regulations, these were referred to as Systems. System 1 became Natural Ventilation with Intermittent Extract Fans and Background Ventilators; System 2 which was Passive Stack Ventilation (PSV) has now been removed (but can potentially be used in situations where suitable); System 3 is now known as Continuous Mechanical Extract Ventilation (MEV and d-MEV); and System 4 has become Mechanical Ventilation with Heat Recovery (MVHR).
Alternative ventilation systems, such as Positive Input Ventilation (PIV) could be specified on the requirements of Regulation F1(1) on the basis that “there shall be adequate means of ventilation provided for people in the building” and that compliance can be proven, for example, with a BBA Certificate.
VENTILATION RATES
Another key change in the updated Building Regulations is the increase in the whole dwelling ventilation rates in a property. Between the 2010 and updated versions there has been an increase of 6 l/s per person with a one-bedroom property which was previously at 13 l/s, now 19 l/s. This is a significant increase and will affect decisions in terms of choosing a suitable product to be able to comply with the regulations. In many cases, intermittent fans are no longer suitable for very airtight dwellings.
The requirements for background ventilation in relation to MEV and d-MEV in England have also been changed. This usually takes the form of trickle vents in windows, but through-wall ventilators can potentially be used, however both options usually require factoring in during the design phase as retrofitting can be costly and time consuming.
In the previous regulations, if a property had an air permeability of 5 or greater this was considered to be fairly leaky and therefore no background ventilation was needed. In properties with an air permeability of less than 5 and therefore more airtight, there was a requirement of 2,500 mm² of background ventilators in each habitable room. The latest Building Regulations updates changed all this, to ensure that properties of all air permeabilities use trickle ventilation in habitable rooms.
The ventilation level has also increased to 4,000 mm² per habitable room, and the guidance states that the total number of background ventilators must not be fewer than the number of bedrooms in the dwelling, plus an additional two ventilators.
A further change is the addition of Section 2 and Appendix B to Approved Document F which relate to indoor air quality and volatile organic compounds (VOCs). This includes a list of harmful contaminants, exposure limits, time and advice on action to be taken should the property exceed safe levels. Developers are increasingly looking to specify whole house ventilation systems, even for smaller properties, as they can be a more efficient way to meet the regulations, with MVHR the most effective.
The issue of overheating has been addressed for the first time in the updated Building Regulations, with the release of Approved Document O: Overheating Mitigation, which is causing an additional challenge. The document concentrates on two main methodologies, the Simplified Method and Dynamic Thermal Modelling which look at many variables to determine whether further action is required to reduce the risk of overheating. Requirement O1 states that ‘reasonable provision’ needs to be made in residential buildings to be able to reduce the occurrence of high indoor air temperatures. A fabric first approach is often taken, with mechanical cooling seen as a final option once all other options have been explored.
For housebuilders working to Passivhaus standards, a certified Passivhaus MVHR system is the key to ensuring that buildings can breathe effectively.
In addition, updates to Approved Document L mean that new homes are required to be increasingly airtight. Latest Building Regulations have increased energy efficiency requirements from 70% to 73% and, as a result of the current energy crisis affecting homes, this need to recover heat and save energy is particularly important to homebuyers.
Ruth MacEachern is product manager for EnviroVent