I live in a semi about 7 years old. Occasionally in the rear upstairs bedroom I can smell cigarette smoke coming from next door. ( no one in our house smokes) I understand that the party wall is block on flat and I cannot understand how this can get through, the joist run front to back because the floorboards run across. I was thinking of getting someone to put a small scope up through a hole in the ceiling below to see if there is any blocks missing etc. Would this be a builder or an engineer? Any ideas.