We live in a 30s semi. The boy next door smokes weed. Sometimes its smell comes into my son's room, so strong it's as if he is smoking in there himself. (he's not, he's 5). We can't work out how. There are no holes in the walls. There is a vent, but we have covered this, and for it to be that, the smoke would have to perform a u turn on exiting from next door. What else could it be?
We are not going to approach next door and ask them to smoke elsewhere, neither of us have that kind of confidence, so we need to work out how it's getting in to fix it. Have left a message for friendly builder, but sometimes the collective wisdom of mumsnet can deduce incredible things.