Loft - condensation, inadequate ventilation - how to solve?

[springmachine]

Our loft room has a side window on the gable end.

Other than that I cant see any ventilation.

When I went up there in November I could see that condensation had formed on the north side of the pitched ceiling and caused a patch of mould.

Since then I have left the gable end window locked on open.

I am not too sure if this is actually doing any good at all. In the recent hot and humid weather I can smell the musty mouldy smell in the bedroom below through the hatch.

I am planning on going up there this weekend to clear out anything that doesnt need to be stored up there and clean the mould patch off the ceiling.

Is there a simple way I can prevent the loft from going mouldy again? Do I keep the side window shut or open? As far as I can see there is no other ventilation. There are eves cupboards which have been put in which I assume are covering the original vents.

Im assuming that the internal surfaces of the roofspace are plasterboarded? Are there any ventilation tiles on the roof itself?

Make sure no extractor fans are ventilating up to the loft. Also no holes around pipes through to there especially in the bathroom (or kitchen if appropriate)

Airflow is generally upwards. Warm air, and also water vapour, rise as they are lighter. If you can smell damp in the room below, then the source of water might be in that room (e.g. A shower or leaking radiator) or possibly a leaking pipe in the ceiling.

You don't drape wet washing in your home, do you?

Put a dehumidifier in the loft room.