Opening up the black box on Part F and ventilation


Following the changes to Part F and Part L of the Building Regulations, housebuilders have been set the challenge of balancing carbon emissions with sufficient airflow to keep homes healthy. The importance of ventilation to health and wellbeing has been given prominence in the latest version of Part F. Steve Pearce of Vent-Axia explains more.

In November 2022, COP27 sought to accelerate global climate action through emissions reductions. Building and construction accounted for over 34% of energy demand and 37% of energy and process-related CO2 emissions in 2021. So, it’s no surprise that the new Building Regulations address how to reduce emissions to help meet the UK’s carbon targets as we move towards the Future Homes Standard on the road to net zero. For housebuilders, this has meant a significant cut in carbon emissions of 30% for new homes, setting a challenge for housebuilders to improve both energy efficiency and airtightness of homes. However, as well as being tasked with making these carbon reductions, housebuilders also need to increase ventilation. As buildings become more airtight to improve efficiency it is essential to consider indoor air quality (IAQ) as well to protect the wellbeing of inhabitants.

Part F’s publication heralds a vital step to improve IAQ with it setting out “significant changes”, which will drive adoption of low carbon ventilation as an industry standard and improve the quality of the air we breathe in buildings.

The new 2021 edition of Part F, L and O took effect on 15 June 2022 in England, but there is a 12-month grace period, which ends in June. Historically Building Regulations applied to each site but following the end of the grace period, each individual plot must follow these regulations in order to comply. This means if a site designed to previous regulations hasn’t started every plot by June, any remaining plots would need to be redesigned to meet the 2021 edition. 


The focus on ventilation has increased in Part F to support the safety of residents, meaning housebuilders are making an overall move to more advanced ventilation solutions, such as Mechanical Ventilation with Heat Recovery (MVHR). However, MVHR is not the only ventilation solution that complies. Housebuilders can instead opt for Continuous Mechanical Extract Ventilation (MEV) in combination with decentralised MEV (dMEV).

MEV and dMEV provide a simple and effective solution to help housebuilders meet the Building Regulations and the Future Homes Standard. The Standard requires new build homes to have world-leading levels of energy efficiency, including a further lowering of Dwelling Emission Rates (DER) as part of the drive towards carbon neutrality.


What alternative does MEV offer to MVHR? A reliable, highly efficient, quiet and easy to operate ventilation system is key to unlocking a healthier, greener future. MEV is a whole house extract ventilation system that extracts air continuously at a low rate. It is a low energy ventilation system designed with multiple extract points to simultaneously draw moisture laden air out of wet rooms, bathrooms, kitchen, WC’s and utility rooms providing a quieter and more efficient system compared to separate fans.

Some MEV units will include a humidity sensor, designed to increase the fan speed in proportion to relative humidity levels, saving energy and reducing noise. Other models include a CO2 sensor, meaning when you have increased occupancy in a home, the unit will increase ventilation rates to ensure the best indoor environment.

Housebuilders should look for a MEV unit that offers market-leading efficiency combined with ultra-quiet performance and sufficient airflow. This will help housebuilders meet DER requirements and improve IAQ for homeowners. Housebuilders should also look at the PCDB list for the best performing MEV systems, with some boasting a specific fan power as low as 0.14 W/l/w and airflow of up to 159 l/s. 

There are even MEV units available that are made from recycled plastic, keeping plastic in the circular economy rather than landfill.


What type of ventilation is dMEV? A decentralised Mechanical Extract Ventilation (dMEV) system is a low energy, continuous mechanical extract ventilation system designed to draw moisture laden air out of wet rooms, bathrooms, kitchen, WC’s and utility rooms providing a quieter and more efficient system compared to intermittent fans. They also ensure good IAQ as they continuously extract the stale air out of the room and ensure it is replaced by fresh air via trickle vents.

High-pressure development and a silent mixed flow impeller mean dMEV units can meet the ventilation requirements of many domestic installations without the need to use a traditional centrifugal fan. Housebuilders opting for this technology should choose a unit that’s been tested to the new SAP 10 performance requirement and listed in the PCDB. dMEV units can achieve exceedingly low SFP values as low as 0.08 w/l/s, combined with almost silent operation at 7.4 dB(A), protecting households from noise pollution. A single high efficiency EC motor delivers these low specific fan powers. 

Housebuilders should also look for dMEV units with an IPX5 rating that allows installation in Zone 1, 2 and 3; the option of 100 mm and 125 mm models; and with variable speed setting for easy installation and commissioning. Units that provide fully adjustable airflow mean whole house rates can be achieved easily using fewer fans, delivering increased ventilation rates at the lowest sound levels with the fewest
fans, helping housebuilders meet ventilation requirements. 

Whether you choose MEV or dMEV, look for units that offer an easy-to-operate control platform, compact design, easy installation, as well as simple and accurate commissioning. And ranges that feature a wealth of control and switching options give housebuilders the flexibility to provide a solution for any new build scenario. 

With the deadline for meeting Part F and Part L of the Building Regulations upon us, housebuilders should look for ventilation that helps them meet DER requirements while improving IAQ. Other growing trends include opting for ventilation with a low SFP and ultra-low noise levels. 

As we move towards the Future Homes Standard and net zero, our homes will become ever more airtight to meet CO2 targets and so it’s essential that energy efficient ventilation is installed in every new home to ensure healthy homes in the future.

Steve Pearce is NBR product manager at Vent-Axia