Through lot

A through lot extends from one street to another roughly parallel street, giving it two street lines at opposite ends and no rear lot line. Its distinctive obligation is the rear yard equivalent: since there is no rear lot line for the usual rear yard, the rules require comparable open area within the middle of the lot, preserving the block-interior light that paired rear yards provide elsewhere.

The mid-lot open area is exactly where a naive design would put its deepest floor plates, which is why through lots surprise back-of-envelope massing. Double frontage is real value — two addresses, two exposures, service from one street and entry from the other — but it arrives with its own geometry.