Vested rights

Vested rights is the doctrine answering what happens when the rules change mid-project: a development sufficiently advanced under lawful permits may generally complete under the prior rules rather than the new ones. How far is far enough is the doctrine's whole difficulty — the analyses weigh construction progress and expenditures made in good-faith reliance on valid permits, and statutory provisions supply specific tests in defined situations.

The doctrine matters most in the interval between a rezoning's announcement and its adoption, when owners race to establish positions the new rules cannot undo. In records, a building inexplicably generous for its district sometimes traces to exactly this race — permits vested days before a downzoning took effect.