Why the ADU Rulebook exists

Accessory dwelling units might be the single most practical answer to the housing shortage: they add homes to neighborhoods that already have streets, schools, and utilities, and they let families keep people close (parents, adult kids, renters) without moving.

But anyone who has tried to build one hits the same wall: nobody can tell you the rules. ADUs are regulated simultaneously by state law, county code, and city zoning ordinances. Each is published in a different place (a planning department page here, a 400-page zoning PDF there, a municipal code portal from 2009), and each changes on its own schedule.

The ADU Rulebook is the directory we wished existed: 410 cities and counties across 41 states, every entry linking to official government sources only, each stamped with the date we last verified it. No paraphrased summaries that quietly go stale; just the actual rules, one search away.

How we keep it accurate

• Every link points to a primary source: the city, county, or state's own website or municipal code.
• Every jurisdiction displays its last-verified date (directory-wide: July 2026).
• Readers can report corrections and request cities; every submission is checked against the official source before publishing.

What the ADU Rulebook is not

It is not legal advice, and it doesn't replace your planning department. Zoning is applied parcel by parcel, and only your local government can tell you definitively what your lot allows. What we can do is make sure you walk into that conversation having read the same documents your permit reviewer will use.