The fan is only one part of ventilation
An extractor fan can help remove humid air after a shower, but its performance depends on the entire route from the bathroom to the outside. A powerful-looking fan connected to a long, restrictive duct with several bends may not perform as expected.
The fan, duct diameter, length, bends, termination and replacement air should be planned as one system.
Do not exhaust into the roof space
Moist air should be discharged to an appropriate external location rather than released into a roof void. Sending warm, humid bathroom air into an enclosed roof space can move the condensation problem out of sight without removing it.
The route also needs to be checked against the building, roof and body-corporate requirements where those apply. An apartment solution may be different from a freestanding house.
Replacement air matters
If a room is sealed tightly, the extractor has less air available to remove. A suitable undercut, transfer route or other planned source of replacement air may be needed, depending on the room and the system.
The door should not need to be left wide open as the only way for the fan to work. That is a sign the ventilation arrangement deserves another look.
Ventilation does not replace waterproofing
Good extraction helps with condensation, mirrors, mould risk and persistent humidity. It does not repair a leak, failed waterproofing, leaking waste or damp caused by a building defect.
In humid coastal Durban homes, both wet-area construction and ventilation deserve attention. One controls liquid water; the other manages moisture in the air.
Read more about the Signature Bathrooms process at our renovation process.
Continue planning your renovation
For a related question, continue with related bathroom renovation guidance.