Ventilation in under the stairs toilet/washroom

[jrsk]

We are having a toilet/washroom installed in the area under the stairs in our house. The builder says we don't need an extractor fan, but my initial reading of the building regs suggests that we do. Am I missing something? Is this a guideline or a hard rule?

[arbco]

Unless the WC has a window with a suitable ventilation opening, or PSV then the simple answer is yes.