[longtermmemmory]

so they need to sue the builder for building a town house so poorly that mere smoke smell can pass through.

There IS case law for nuisance smells.

Seems to me that they needed to mitigate their smoking somehow so it would not affect the neighbors in the attached townhouse.

This is a neighbor scenario, not a smoking scenario.

[elkfersupper]

so they need to sue the builder for building a town house so poorly that mere smoke smell can pass through.

An excellent conservative notion and tactic.....not.