Internal walls

Building Regulations: Ventilation

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 a typical area of at least 1/20th of the floor area of the room served, unless it is a bathroom which can be any openable size.

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 - 5,000 mm² equivalent area
  • kitchen, utility, bathroom (with or without WC) - 2,500 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.

Mechanical extract fans

Any new kitchen, WC with no openable window, bath/shower room or utility room should be provided with a mechanical extract fan to reduce condensation and remove smells.  The necessary performance of these extract fans is normally measured in litres per second (l/s) as follows:

  • Kitchen - 30l/s if placed over the hob and 60l/s if place elsewhere
  • Bath/shower - 15l/s with an additional 15 minute overrun (after the light is switched out) if there is no openable window
  • WC - 6l/s with overrun
  • Utility room - 30l/s.

Alternative rates may be applicable if the ventilation is running continuously.