> I don't know about annoying neighbors and smells.

If you live in a lower income area, get used to your condo/townhouse occasionally smelling like marijuana and/or tobacco whenever the neighbors decide to hotbox. Also get used to arguments and loud music late at night on weekends.

> That seems to be a design and engineering issue.

I'm sure you could build hermetically and acoustically sealed condos that keep out all unwanted noises and smells, but those sound like "rich people" condos that are not very economical.