ADU permit requirements by state & city

Common questions

Do I need a permit to build an ADU?

Yes. An accessory dwelling unit is habitable space, so building one requires a building permit from the local authority that issues permits for the property, and in most jurisdictions a zoning or planning review as well. Several states also have a statewide ADU law that sets baseline standards local agencies must follow. The per-state guides below flag which ones do.

What documents does an ADU permit application require?

It varies by jurisdiction, which is the whole problem. Common items across the guides are a scaled site plan, floor plans and elevations, a structural or foundation plan, an energy compliance form, a plumbing and mechanical layout, a soils or geotechnical report where the site calls for one, and utility or water service confirmation. Each guide lists that jurisdiction's actual items with a source link and a last-reviewed date.

Are these permit guides free?

Yes. Every state and city guide is free to read with no account and no signup. Each requirement carries a citation to a government source and the date it was last reviewed, so you can verify it yourself.

How current is this data?

Each jurisdiction carries its own last-reviewed date, shown on its guide page and in the page's structured data. Codes change on multi-year cycles and local amendments change more often than that, so treat the guide as a starting point and confirm the exact forms, fees, and code edition with the permitting authority that will issue the permit.