Bathroom extractor fans: wall, loft or roof route?

A replacement fan in an existing opening is different from a new extraction system. When starting from scratch, the best route depends on the room position, outside walls, loft access, duct length and a suitable termination point.

Direct through an outside wall

A core-drilled wall route is often the most direct solution. A timer or humidity-sensing fan can be supplied and fitted with a short route to outside. Truvo uses about £450 as the starting point for a suitable new direct-wall installation, subject to the electrical supply, wall construction, access and final specification.

Through a loft to a wall or soffit

An upstairs bathroom may use an inline loft fan and duct to an appropriate external terminal. The duct must be routed and supported sensibly. Long, cold or poorly arranged ducts can collect condensation and reduce performance.

Through the roof

A roof terminal may be appropriate when there is no suitable wall or soffit route. Roof covering, weathering detail, safe access and responsibility for specialist roofing work must be agreed. Slate, flat and difficult roofs need individual assessment.

Controls and electrical work

Common options include operation with the light, a run-on timer, humidity sensing, PIR control or a separate boost switch. Bathroom zones, isolation and the existing circuit all affect the design.

Persistent mould or moisture can have more than one cause. Extraction should discharge outdoors, but heating, insulation, air paths and building defects may also need attention.