My mother lives in a large 1930s bungalow and one of the spare bedrooms has a nasty musty smell. I noticed it on going in there when she was on holiday. The house had been shut up but the smell was not in any of the other rooms. It has a redundant chimney in it and I noticed that there was no air vent fitted to the chimney. The smell is not coming from the bed, furniture or the cupboard. There are no visible damp patches and the brickwork outside is sound. The flooring is made of floorboards covered by a carpet. I am worried that she may have dry rot under the floor. Before I upset her by ripping up the carpet to check can anyone tell me what dry rot smells like?

Dry rot of wood is almost odorless so I think you need to think of something else. Smells are hard to track because they drift so easily. Is that a rug or wall to wall carpet?

Fireplaces and chimneys that have been used but are not currently in use usually have an odor. This is particularity true with high humidity. Try temporarily blocking the fireplace to see it the odor is abated.