Extractor fans, mould and ventilation

Mould right round a fan says damp is reaching the ceiling and staying. It does not prove the fan is broken, so ask in order. Does it start with the light and carry on afterwards? Is it moving air (a sheet of tissue held to the grille will show)? Is the grille clogged? And where does the air go? Approved Document F expects bathroom extract to go to the outside², so ducting that ends in the loft is a question for the fitter. UKHSA says fans should be kept maintained¹.

High on the wall, clean, with a clear grille, as here. UKHSA says fans can be controlled by humidity, or linked to the light with an overrun so they carry on after you leave¹. Approved Document F gives new-work rates of 15 litres a second for an intermittent bathroom fan and 8 for a continuous one²; those are installers' design figures, not a test you can run. What you can notice is noise, whether it stops the instant the light goes off, and whether the mirror still steams.

For showering, UKHSA advises opening windows and closing internal doors so the steam doesn't travel round the home¹. A vent beside a window, as here, only lets air out if it is open and clear. Check it hasn't been painted shut, stuffed with a towel or furred with dust. A vent with no fan relies on warm air rising, so it helps but is not a fan. If the bathroom has no fan at all, an electrician is the person to ask about one: a fan sits close to the zones in the electrical zones page.

Specks on a curtain or liner show damp hanging about on a soft surface. Spread the curtain out after each shower so it dries rather than bunching, and look at the hem, the folds and the bottom edge. Mould that returns after cleaning is the cue to look at the cause, not the curtain: ventilation, a cold wall, a leak. UKHSA names asthma, COPD, weak immune systems, pregnancy, children, older people and people who are housebound as more vulnerable to damp and mould¹. If someone like that lives there, do not wait.

Moisture that doesn't leave as vapour ends up on the coldest surface: the window, an outside wall, the ceiling. A window running with water after a shower says the room's moisture has nowhere to go. Wipe the glass and sill so water doesn't soak into the frame, then notice how long the window takes to clear with the fan on and the door shut. If it stays wet for hours, ventilation is short. Central Bedfordshire Council has a short film on damp and mould that covers the same ground.