ADU rules are a mix of state statutes, agency guidance and city ordinances, and they change often. This page explains how we decide what to publish and what to leave out.
Source hierarchy
- Primary law: the statute or ordinance text itself (for example California Government Code, Revised Code of Washington, Oregon Revised Statutes, Arizona Revised Statutes).
- State agency guidance: pages and handbooks from the agency that administers the law, such as California HCD or the Colorado Department of Local Affairs.
- Official city pages and handouts: the planning department materials that describe how a city applies the rule.
- Secondary sources: academic briefs and reputable news reports, used for context and never as the only support for a number.
We do not use anonymous forum posts, contractor marketing pages or unsourced summaries as support for a rule.
What we check before an article is ready
- Every number (square feet, feet, days, dollars) is traced to a source.
- Section numbers are checked against the current statute, including renumbering.
- Claims about effective dates and amendments are checked against the bill or ordinance history.
- Statements we could not confirm are removed or marked as unconfirmed, with a pointer to ask the city.
What “Last verified” means
The date at the top of each guide is the day we last compared its claims with the sources listed. It does not mean the law has not changed since. Where we know a change is pending, the article says so.
When sources conflict
If a city page and a statute disagree, we report the statute as the state minimum, report what the city says, and tell you to confirm with the city. We do not pick a winner silently.
Limits
We cannot see how a specific planner will read a specific lot. Use our guides to prepare questions, not to replace the answer. See also our editorial policy.