MB4 264b: Including Structures Outside the City Borders and Techum (398:5-6)

Any structure within 70 2/3 amah of a city (when squared off) is included in the city and constitutes the beginning of the 2000-amah techum. This only applies to a "בית דירה" even if it's not currently used as one.

Adding 70 2/3 amah before calculating the 2000-amah techum of a city (עיבורה של עיר)

Multiple houses each 70 2/3 amah away from each other beyond the city.

Definition of "בית דירה".

A guardhouse (e.g. a house guarding a storehouse) or a building that fell into disuse.