airbrick sized holes. Or you could hire a core drill for a day and make big round holes.
Also, look for sources of damp such as plumbing leaks. Is there a clay gulley outside? It will be cracked. Is there a steel waterpipe? It will be leaking. Is there a downpipe? Spilling. If this is a coalhouse, there will be a chute leading to the front path. Probably badly blocked with rubble and a paving stone.
Do you have a watermeter? Observe the bubble, when all taps are turned off.
Also, look for sources of damp such as plumbing leaks. Is there a clay gulley outside? It will be cracked. Is there a steel waterpipe? It will be leaking. Is there a downpipe? Spilling. If this is a coalhouse, there will be a chute leading to the front path. Probably badly blocked with rubble and a paving stone.
Do you have a watermeter? Observe the bubble, when all taps are turned off.