Our spare bedroom has a flat roof and used to be our office. The outside corner wall had signs of damp and smelt musty/damp and we then repaired a leak in the flat roof on that corner. The smell seemed to improve for a while but now it's back. Using a damp meter there are no signs of damp in the walls and we have just removed the ceiling and fibre class insulation to reveal the wooden roof supports. The damp meter isn's showing any damp in the supports or the wooden roof, so where is the horrible smell coming from? Help!

From the mold that started growing on your wood 48 hours after the leak started. Once wood gets wet repeatedly it will mold and mildew causing a awful smell. Since the underside of the roof is open now I'd spray it with silver/aluminium paint to seal the odor or KILZ 2. The inside of the walls are probably just as bad. Are you ready for the next step?