Internal walls

When inserting a new internal wall care must be taken not to make any other matters, such as ventilation worse.

If a new room is being created as a result of  the addition of an internal wall then care must also be taken to ensure that the existing room is ventilated adequately. The type of room will determine how much ventilation is required.

The general rules for ventilating a room are:

Purge - this is achieved by opening the window. The opening should have an area of at least 1/10th of the floor area of the room if the opening angle is between 15 to 30 degrees. If greater than 30 degrees then it should have an area of at least 1/20th of the floor area of the room. Any hinged or pivot window which opens less than 15 degrees is not suitable for purge ventilation.

Whole Building - this is also known as trickle ventilation which can be
incorporated in to the head of the window framework, or by some other means. The area varies on the type of room:

• Habitable room or kitchen in building with multiple floors - 8,000 mm² equivalent area
• Habitable room or kitchen in buildings which are single storey - 10,000 mm² equivalent area
• Bathroom (with or without WC) - 4,000 mm² equivalent area

Both of these forms of ventilation are normally required, however alternative approaches to ventilation may also be acceptable, subject to agreement with the Building Control Body.

Extract ventilation

Any new kitchen; bathroom (or shower room); utility room; or toilet should be provided with a means of extract ventilation to reduce condensation and remove smells.

For toilets only, ‘purge ventilation’ (an opening window/door on an external wall) meeting the requirements specified in section 1, page 11 of ‘Approved Document F - Ventilation¹’ can instead be used to provide ventilation if security is not an issue.

Any extract ventilation system you install should meet the requirements specified in section 1, page 8 of ‘Approved Document F - Ventilation²’.

1. https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents/part-f-ventilation/approved-document-f-volume-1-applies-to-dwellings
2. https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents/part-f-ventilation/approved-document-f-volume-1-applies-to-dwellings