Trickle Vents in replacement windows and doorsets

Since June 15^th 2022, new building regulation guidance has applied in England concerning the provision of background ventilation (trickle vents) in replacement windows and doorsets.  Many BWF members who supply these products for use in historic buildings have raised concerns that the new guidance calling for them to potentially fit two full sized trickle vents into their windows or doorsets would not only be difficult to achieve, but would not be wanted by their clients. Furthermore, they may not be in keeping with the historic context of the homes on which they are working. This blog will provide an overview of the new guidance which may prove useful to all woodworking businesses who provide replacement windows and doorsets.

The full guidance for the provision of background ventilation in replacement windows and doorsets for existing houses or flats (dwellings) is given in the 2021 edition of approved document F volume 1 which is available online. Further guidance on the building regulations and the approved documents is given in the Manual to the Building Regulations which is also available online.

Work to the following types of historic and traditional dwellings may not need to comply fully with the ventilation guidance in approved document F,

• Those listed in accordance with section 1 of the Planning (Listed Buildings and Conservation Areas) Act 1990
• Those in a conservation area designated in accordance with section 69 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
• Other historic buildings with a vapour-permeable construction that both absorbs moisture and readily allows moisture to evaporate. These include those built with wattle and daub, cob or stone and constructions using lime render or mortar.

Work to these dwellings should comply with the ventilation standards in approved document F where reasonably practicable but the work should not result in either of the following outcomes.

• Unacceptably affect the significance of the listed building, conservation area or scheduled monument.
• Increase the risk of long-term deterioration of the building fabric or fittings.

The local authority’s conservation officer should be consulted when undertaking work dwellings described above.

The guidance in approved document F for the provision of replacement windows into existing dwellings is as follows,

• If the existing windows have background ventilators, the replacement windows should include background ventilators. The new background ventilators should comply with both of the following conditions.
  • Not be smaller than the background ventilators in the original window.
  • Be controllable either automatically or by the occupant.

If the size of the background ventilators in the existing window is not known, the ventilator sizes shown below may be applied.

• If the existing windows do not have background ventilators it is necessary to ensure that the ventilation provision in the dwelling is no worse than it was before the work was carried out. This may be demonstrated in any of the following ways.
  • Incorporating background ventilators in the replacement windows equivalent to the following.
  • Habitable rooms – minimum 8000m m2 equivalent area.
  • Kitchen – minimum 8000mm2 equivalent area.
  • Bathroom (with or without a toilet) – minimum 4000 mm² equivalent area.
• If the dwelling will have continuous mechanical extract ventilation, installing background ventilators in any replacement windows which are not in wet rooms, with a minimum equivalent area of 4000 mm² in each habitable room.

NOTE: If it is not technically feasible to adopt the minimum equivalent areas given above, the background ventilators should have equivalent areas as close to the minimum value as is feasible.

• Other ventilation provisions, if it can be demonstrated to a building control body that the ventilation of the dwelling is not less satisfactory than before the work was carried out.

For further information and assistance contact Kevin Underwood kevin.underwood@bwf.org.uk