I was reading a thread from a mum of a 5 year old who seemed to be having the same problem a me! The occupent of a 1930's home her son's room was being suturated with the smell of weed from the next door neighbour. My second bedroom and landing area are similarly saturated and without virtual continuous air movment from fan or keeping the windows open my whole house is saturted. It is coming through from the loft. Apparently when these houses were built the cavities in the bricks were not sealed in the loft space and that is were the smell is coming in. I have been complaining to the police and health and safety for months as this is coursing my family health problems but so far no-one has even spoken to the neighbour about his habit. It seems my only option it to get the loft space sealed at my own expence so the neigbour can continue his illigal habit in comfort!