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The long-awaited update to Building Regulations was announced in December 2021 - a significant update that focuses on the existing energy efficiency standards for homes and marks a steppingstone towards the introduction of the Future Homes Standard in 2025.

The new Building Regulations comprise five new documents, with the ones that mainly affect our industry being Part L (heating and energy) and Part F (ventilation). This will come into effect from 15 June 2022, and will have a marked impact, particularly on new, but also on existing homes.

Each country has their own guidance and, for now, we will concentrate on the regulations for England.

Part L

Presently U-Values are 1.4W/(m2K) for windows going into new homes, and 1.0-1.4 W/(m2K) for doors depending on glazing. Under the Part L 2022 changes, these will be 1.2 W/(m2K) for windows and 1.0 W/(m2K) * for doors. For refurbishments in existing buildings, there are higher figures of 1.4 W/(m2K) for windows and doors.

It’s worth noting that these figures are based on desirable values to be inputted into SAP when Building Regulations calculate the ‘notional building.’ They aren’t used in isolation, and they’re also not absolute, to allow for flexibility in building design

To put it simply, the notional building is a digital shadow of the exact building and uses fabric values issued by the government through Building Regulations. Several exact values are entered into SAP for things such as thermal properties, space heating and air tightness. These are then compared with the notional building. If a window doesn’t meet a value of 1.2, (if it is a Vertical Slider for example), a limiting value can be applied and other areas of the dwelling can be improved to offset this, such as better insulation. The limiting value is the worst value a product can perform at.


Part F

Approved Document F has caused a lot of controversy in the industry since being published. For new build, the requirements are:

The new regulations will also require most replacement windows and doors to be fitted with trickle vents dependant on the room type, volume of windows/doors fitted and if sufficient proof can be provided that the installation does not make the ventilation situation any worse.
For existing windows with trickle vents already in place there is no discernible difference to the current regulations, that is:

  • The replacement vents cannot be smaller than the ones in the window that is being replaced
  • If the size of the trickle vent in the windows being replaced is not known then the replacement trickle vent should be sized as such:
  1. Habitable Rooms and Kitchens – Equivalent Area of 8000mm²
  2. Bathrooms (with or without a toilet) – Equivalent Area 4000mm²
  • They must be controllable

When replacing existing windows that do not currently have trickle ventilators, the base position is that Trickle vents should be installed as below:

  • Habitable Rooms and Kitchens – *equivalent area of 8000mm²
  • Bathrooms (with or without a toilet) – *equivalent area 4000mm²

If the property has “continuous mechanical extract ventilation”

  • Trickle ventilators with a minimum *equivalent area of 4000mm² should be installed in any replacement windows which are not in wet rooms (e.g. bathrooms, kitchens, utility rooms)

If it can be demonstrated that they comply with the requirements, “other ventilation provisions” may be used.

*If it is not technically feasible to adopt the minimum equivalent areas set out then trickle vents with the closest possible equivalent area should be used.

This change to Part F will mean approx. 90% of all replacement windows will now require trickles vents compared to the current level for replacement windows which is approx. 30%.


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