Example: a neighbor's smoke reaching an upper-floor unit

The situation

Illustrative example. Not a real job or customer.

An owner has lived in an upper-floor unit of a mid-rise building for several years without problems. A new resident moves in on a lower floor. Starting with the first cold weather, the owner smells fresh cigarette smoke most evenings in the primary bathroom and the bedroom closet that backs onto it. On mild days and all summer, there is nothing.

1. The owner starts a log: time, location, strength and weather. After three weeks a pattern is clear: cold, still evenings, strongest under the bathroom sink.
2. Removing the sink cabinet's back panel reveals a large unsealed gap where the plumbing riser passes through the wall.
3. With approval from the building manager, a contractor seals the gap around the riser with an appropriate fire-rated sealant, and the owner adds foam gaskets behind outlet covers on the shared wall.
4. The owner sends the log to the manager, without naming a neighbor, and asks how the association's rules treat smoking inside units.
5. Maintenance checks the riser chase from other units and finds similar unsealed gaps on several floors, which the association addresses as a building repair.
6. The board sends a general notice to residents about smoke traveling through the building and reminds owners of the existing rules.
7. The owner cleans the bathroom and closet surfaces where a light film had built up over the winter.

The smell drops from most evenings to occasional faint traces on the coldest nights. The owner keeps logging into the next winter to see whether further steps are needed.