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Changes in the FLO regulation: how they affect Wales in November 2022?

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By Ruth MacEachern

Product Manager

Jan 09, 2023

The section of the governmental building regulations that addresses ventilation and air quality in buildings is known as Approved Document F. The Approved Document was first introduced in 2010 and has recently been amended to incorporate new terminology, an increase in whole dwelling ventilation rates, adjustments to background ventilation rates, and guidance relating to indoor air quality and the content of volatile organic compounds in the air. The document and the amendments in question have already been discussed at length in several of our previous blog entries (see below), however, if you are a house builder or technical director based in Wales, the schedule of amendments and the dates for the coming into effect of the new FLO regulations differ slightly to the rest of the UK. In this article we will look at how these changes will affect domestic property developers in Wales, highlighting some key dates for your diary. For more details information on revisions to the building regulations and their practical application, check out our related articles here, and also here.

What do we mean by FLO regulations?

The abbreviation FLO refers to Approved Documents F, L, and O of the governmental building regulations. The table below identifies the subject matter addressed in each of the documents:


Subject addressed

Approved document F

Provisions for ventilation within buildings

Approved document L

The conservation of fuel and power

Approved document O

The overheating of buildings

Envirovent being experts in the field of ventilation, this article will naturally focus on the new ventilation changes stipulated in Document F, however, we will first look very briefly at the other two documents that make up what we are referring to collectively as the FLO Regulations.

Changes to Approved Documents L & O

Document L, concerning the conservation of fuel and power, is relevant to building ventilation on account of the fact that ventilation systems consume electricity and remove heat from the building (and in the case of MVHR systems feed heat into the home). The main ventilation-relevant change to Document L is this:

  • Heat recovery systems are now required to be 73% efficient, an increase of 3% on the previous specification. As Envirovent’s heat recovery systems boast an efficiency well in excess of 85%, this change raises no cause for concern.

Document O highlights two methods by which to demonstrate compliance with overheating regulations, namely a simplified method and the more complex option of dynamic thermal modelling. It further stipulates that mechanical cooling may be used to reduce overheating, but only if the temperature cannot be otherwise reduced through the addition of shaded areas or the removal of warm air by means of ventilation. Finally, it may be that the standardized purge rate in properties which is 4 Air Changes per Hour (ACH) is no longer deemed to be acceptable. This may require increasing to ensure compliance with Approved Document O. In this case, larger fans or alternative ventilation systems may be required, though it is always worth checking with a specialist consultant and looking into an overheating report on the property.

Key changes to Approved Document F

The main changes introduced through the amendment to document F are as follows:

- Terminology changes, replacing the previous numbered system.

- An increase in whole dwelling ventilation rate – intermittent ventilation (extractor fans) is now only suitable for “less airtight” buildings, whereas an alternative ventilation strategy, e.g. MEV/MVHC, will now be required for buildings with an as-built air permeability rating of less than 3 m3/3 h.m2 @ 50Pa (“highly airtight”).

- A considerable increase in minimum whole building ventilation/air flow rates. These can be found in Table 1.3 of the document.[1]

- Changes to the regulations for background ventilation (e.g. window trickle vents), with requirements now stated per habitable room and by type of room rather than based on the total floor area.

The Welsh government has provided a Home Energy Guide template, to be issued to new homeowners, which will also assist you in the fulfilment of your new regulatory obligations, available here.

Key dates for Wales


Whereas the interim regulatory changes to the FLO regulations came into effect in June 2022, in Wales the key dates for your diary are:

  • 23 November 2022 - Interim parts L and F came into effect
  • 2023 – Further review of part L for the Future Homes Standard & Building Standard
  • 2025 – Part L FHS Regulations come into effect


While changes to Approved documents L and O are definitely worth considering when planning and executing the ventilation within your new build project, it is the changes to Approved Document F with which developers really must get to grips if they are to ensure compliance. With Envirovent systems in many cases far exceeding the performance levels required under the new regulations, and with a team of experts on hand to assist with product selection, installation, commissioning, and the demonstration of compliance, you can remove unnecessary stress from your project by choosing Envirovent.