Bathroom ventilation

Q.    I recently had a question from a member that was having a disagreement with a client over the ventilation requirements in a bathroom.  The issue concerned the installation of an exhaust fan in a bathroom and whether it was required to be vented to the outside of the building via ducting or whether it could be vented into the roof space.

A.    Volume 2 of the BCA covers ventilation requirements for housing in Part 3.8.5.  The Acceptable Construction Practice is specifically covered in Clause 3.8.5.2 (a), (b) and (c).

Whilst most modern bathrooms contain an exhaust fan of some description, we need to look more closely to the application of the rules to ascertain its standing.

• Firstly, if a window is installed in the room, then it becomes the primary source of ventilation for the room. Therefore, irrespective of whether an exhaust fan is installed, if the room in question has a window installed in accordance with the provisions of sub-clause (a) then the ventilation requirements for the room complies with the BCA.
• Similarly if the room has ventilation borrowed from an adjoining room in accordance with sub-clause (b) it also complies with the BCA.
• If installed, an exhaust fan only needs to comply with sub-clause (c) if it is the only source of ventilation to the room.

Therefore in accordance with sub-clause (c), exhaust fans are not required to be directly ventilated to the outside where the roof space contains:

• open eaves;
• roof vents, including a vented ridge;
• a tiled roof without sarking;

So in short, exhaust fans and range hoods are not mandated by the BCA and are therefore not required to be directly vented to the outside of the roof space.