Changes to Building Regulations ‘Approved Document F, Volume 1: Dwellings’ (ADF1) came into effect on 15 June 2022. It gives guidance on how to comply with Building Regulations Part F Ventilation and applies to dwellings identified as self-contained units. For blocks of flats with shared communal rooms, ‘Approved Document F, Volume 2: Buildings other than dwellings’ applies.

However, not all new building projects were initially covered under the revised ADF1. Where a building notice, initial notice, or full plans for building work that were submitted to a local authority before 15 June 2022, and where the building work commenced by 15 June 2023, compliance with these revised regulations was not compulsory. That means a considerable sway of contractors have yet to work to the new ADF1. However, as of 15 June 2023, the transitional phase is over and now compliance is required by all. Here, we recap the five key changes that you now need to accommodate in your ventilation design.

Increased ventilation rates

Across all sizes of properties, minimum ventilation rates, now based on the floor areas and number of bedrooms per property and no longer with predicted occupancy rates (which required a level of guess work and, ultimately, uncertainty), have been increased as follows:

No. of 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

These increases are significant, especially when it comes to larger properties, and reflect the concern that previous ventilation levels were insufficient to reach all parts of a home, especially the bedrooms overnight if doors are kept shut. 

To achieve these new ventilation rates, relying on natural ventilation is almost certain to end in failure. Instead, mechanical ventilation systems in the form of Mechanical Extract Ventilation (MEV) and Mechanical Ventilation with Heat Recovery (MVHR) are the most proficient option; in the case of larger properties with minimum ventilation rates up 43l/s, they really are the only option and will mean choosing mechanical systems with greater fan power than previously required.

Background ventilation sizing

Background ventilation is the passive supply of external air into a room via ‘a small ventilation opening’, such as intermittent extract fans, trickle vents in windows and airbricks in the wall. These now need to be sized differently under the revised ADL1. 

Previously, the size of the background vent was determined by the size of the property. Now, this is to be calculated on a room-by-room basis to ensure adequate ventilation throughout a property. This is likely to mean an increase in the number and size of background vents. Certainly, it will mean considerably larger grilles are required, which aren’t aesthetically pleasing and can’t be covered up.

In the case of extract only systems, such as MEVs, the background vents size has been doubled from 2,500mm2 to 5,000mm2, which is likely to have implications for the property’s façade and window sizes.

Natural ventilation options reduced

Natural ventilation systems, such as the background vents mentioned above, are now only an option for less airtight homes with a design air permeability of ≥5.  Passive Stack Systems, which work on the principle that warm air rises and gets sucked out at the top floor while cool air enters through trickle vents to replace it, have also been removed as an option.

Natural ventilation should not be at the core of any modern building design as it cannot deliver the ventilation rates required and is inefficient as heat is lost alongside the stale air.

Compliance: no excuse for failure

One important issue that was highlighted when reviewing Building Regulations was the lack of compliance; ventilation systems were not meeting the old standards, so how on earth would they be met if those standards were to increase (as they now have done)? Depending on your perspective, this lack of compliance has been attributed to the complexity of the requirements causing confusion and a lack of understanding, or through the deliberate flouting of them.

As we have seen, the revised ADL1 has simplified the calculations by removing the need to predict occupancy rates. At the same time, reporting has been tightened up to drive compliance. 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.

Addressing air pollution

In 2021, the UK was found guilty by the European Court of Justice of “systematically and persistently” breaching air pollution limits. The key emissions sources of the most common and dangerous pollutants – NO2 and PM2.5 – are transport and domestic fossil fuel burning respectively. 

For those living near busy roads and in urban areas, these emissions readily enter homes around closed doors, through windows etc. Pollution is also generated by activities conducted within the house, including cooking and cleaning.

Consequently, the latest ADL1 places greater emphasis on combatting both internal and external air pollutants more thoroughly. It looks at exposure limits and times for carbon monoxide (CO), nitrogen dioxide (NO2), formaldehyde (CH2O), and TVOC. 

Recommendations for the placement of intake grilles away from the direct impact of the sources of local pollution are provided. 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.

A combined step forward

Part F of Building Regulations cannot be read in isolation; it is closely tied to Part L (Conservation of Fuel & Power) which is a driving force for the changes to Part F, and the new Part O (Overheating). The aim is to ensure that 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 an 80% reduction by 2050, the year set for net-zero.

A decarbonised home is an energy efficient one. In the case of heating systems, minimal energy consumption is essential, as is a move away from fossil fuels, combined with ability for the building to retain that heat through maximum thermal efficiency. But a comfortable, healthy home is one that isn’t just warm, but has clean, fresh air for the inhabitants to breath; and that is only possible through effective ventilation.