The world is a very different place since 2010, the year that Building Regulations ‘Ventilation: Approved Document F’ was previously revised. In the years that have elapsed we have not only learnt considerably more about Indoor Air Quality (IAQ), and pollutants and their impact on our health, but we have also had to contend with a pandemic that has changed our relationship with our home environment.
During this timeframe, albeit more recently, the drive towards the 2050 Net Zero goal has become more intense. To reduce emissions as close to zero as possible, we must decarbonise all sectors of the UK economy, including housebuilding. The Future Homes Standard, which will be introduced by 2025, is the housing sector’s strategy to achieve this. It requires new homes to be considerably more energy efficient, with average homes having 80% less carbon emissions than those built to current energy efficiency requirements. Building Regulations is the method being used to achieve the Future Homes Standard.
Set amongst this context, it is without doubt that Building Regulations Part L (Conservation of fuel and power) and Part F were ripe for an update. After some delay, these were published in December 2021. The aim is to ensure new homes built from 2022 produce 31% less carbon emissions compared to current standards. A further revision will take place to come into force in 2025 to bring that figure to the 80% reduction.
Who Needs to Comply?
If a building notice, initial notice, or full plans for building work have been submitted to a local authority before 15th June 2022 and the building work commences by the same date the following year, the new standards do not apply. For building works after those key dates, the revised Part L and Part F must be followed.
Furthermore, there are no exemptions based on the size of the new build. Under the previous Regulations, smaller developments were exempt from air tightness testing. Now, air tightness testing is mandatory in all new build dwellings. So, when it comes to Part F, all new dwellings have to comply with this aspect. This is necessary if we are to produce the type of airtight low energy buildings laid out in the Future Homes Standard.
But of course, the more air tight we make our homes, the greater the need for sufficient ventilation to maintain a healthy and comfortable atmosphere. The revisions to Part F are a direct response to this requirement. So, what has changed?
Mechanical Ventilation Systems
Mechanical ventilation systems in the form of Mechanical Extract Ventilation (MEV) and Mechanical Ventilation with Heat Recovery (MVHR) are recognised in Building Regulations as the most proficient means of ventilating a dwelling. To ensure incoming air reaches all parts of a home – especially the bedrooms – the minimum ventilation rates have been increased as follows:
| No. bedrooms | Previous min. ventilation rate l/s | New min. ventilation rate l/s |
| 1 | 13 | 19 |
| 2 | 17 | 25 |
| 3 | 21 | 31 |
| 4 | 25 | 37 |
| 5 | 29 | 43 |
For larger properties, this increase is substantial and will mean choosing mechanical systems with greater fan power.
In a much welcomed move, predicted occupancy rates have been removed from the ventilation calculations, making them far more straightforward.
Background Ventilation
Two key changes have been introduced here.
The first is the guidance on sizing background ventilators, including intermittent extract fans, trickle vents in windows and airbricks in the wall. These are to be done on a room-by-room basis rather than the whole property.
The second applies to extract only systems, such as MEVs, where the background vents must be increased in size from 2500mm2 to 5000 mm2. This may well impact on the property’s façade and window sizes.
Natural Ventilation
Natural ventilation systems, such as background vents, remain an option although only for less airtight homes with a design air permeability of ≥ 5. However, with the background ventilation to be determined on a room by room basis, rather than based on the whole property, this will probably mean much larger grilles are required. No matter how well designed the grille is, it is likely to compromise the aesthetics of the property from both inside and out.
Ultimately, natural ventilation isn’t an efficient means of ventilating a home as heat will be lost and there is no guarantee of moisture or pollutants migrating outside.
The other change here is that Passive Stack Systems have been removed as an option.
Positive Input Ventilation (PIV)
Also essentially removed as a practical option under the revised regulations are PIV systems. The only circumstance under which they can be used is if their effectiveness can be clearly demonstrated against the pollutant guidance values and criteria provided. For the majority of people, the extra work required to do this and the uncertainty will effectively rule out PIV as an alternative to MEV and MVHR systems.
Air Pollution Guidance
With air pollution now firmly on the news agenda, and our increasing understanding of its dangers to our health, the revised Part F addresses both internal and external air pollutants more thoroughly.
Useful indoor air pollution guidance has been added, covering exposure limits and times for Carbon monoxide (CO), Nitrogen dioxide (NO2), Formaldehyde (CH2O) and TVOC.
In areas with high level of outdoor pollution, advice has been provided on the location of intake grilles, primarily away from the direct impact of the sources of local pollution. Where urban traffic is a source of pollution, the air intakes for dwellings next to busy urban roads should be as high as possible and located on the less polluted side of the building. Ventilation intakes should not be located in courtyards or enclosed urban spaces where air pollutants are discharged.
Reporting
With many homes unable to comply even with the previous Building Regulations Part F requirements, either through confusion and a lack of understanding of the requirements or through deliberate flouting of them, the reporting procedures have been tightened up under the 2021 revisions.
Now a new style commissioning sheet featuring a compliance report and photographic evidence must be provided to Building Control Bodies and the building owner, along with a Home User Guide specifically for householders.
So much has changed in the eleven years since Building Regulations ‘Ventilation: Approved Document F’ was last revised; some of it predictable, others out of the blue. The changes made to Part F are both a reflection on this, but more importantly look to the future and how we as an industry can meet Net Zero and provide housing fit for purpose.
