Sources & Methodology

Primary Sources: Municipal codes, city zoning ordinances, and official planning department publications.

For each city, we locate the specific municipal code section governing Accessory Dwelling Units (often found under residential zoning chapters). We cross-reference this with the city's planning department website, which typically publishes ADU-specific information sheets, handouts, or web pages summarizing the rules.

What we verify: Allowed zones, maximum unit sizes, height limits, setback requirements, parking rules, owner-occupancy requirements, and lot size minimums.

Primary Sources: City planning department permit pages, published fee schedules, and ADU-specific application guides.

Permit fees and timelines come from official city fee schedules (which most cities publish as PDFs or web pages). Processing timelines reflect state-mandated minimums (e.g., California's 60-day ministerial review) combined with city-reported averages.

What we verify: Approval process type (by-right vs. conditional use), review timeline, permit fees, impact fees, plan check requirements, and pre-approved plan availability.

Primary Sources: HomeAdvisor/Angi contractor cost databases, city-published fee schedules, and regional construction cost indices.

Construction costs are estimates based on regional averages from contractor marketplaces and adjusted for local labor and material costs. We present ranges rather than exact figures because actual costs vary significantly based on ADU type, size, finishes, and site conditions.

Important note: Cost estimates are for general guidance only. Always get multiple contractor quotes for your specific project.

Primary Sources: Zillow Rental Manager market data, HUD Fair Market Rents (FMR), and local rental market surveys.

Rental income estimates represent typical market rents for studio/1BR and 2BR units in each city's metro area. These figures are updated to reflect current market conditions using publicly available rental indices.

Important note: Actual rental income depends on location within the city, unit quality, amenities, and market conditions at the time of listing.

The ADU Score (out of 10) shown on every city page is our summary of how easy a city makes it to build an ADU. It is a transparent composite of the regulatory factors that most affect a homeowner's ability to build, each scored from the same official data we cite on the page:

• Approval path (by-right vs. discretionary) — ministerial/by-right approval scores highest; conditional-use permits or public hearings score lower.
• Size allowance — higher maximum ADU size (e.g. 1,000–1,200 sq ft) scores higher than restrictive caps.
• Setback requirements — 3–4 ft side/rear setbacks score higher than large setbacks that shrink the buildable area.
• Parking — no added parking requirement scores highest; a required space scores lower.
• Owner-occupancy — no owner-occupancy mandate scores higher (it allows pure rental investment).
• Permit cost & timeline — lower fees and faster review score higher.

Roughly: 8–10 = very ADU-friendly (by-right, generous size, no parking/owner-occupancy), 5–7 = moderately friendly (some friction or cost), below 5 = restrictive (discretionary approval, tight limits, or high cost). The score is a guide for comparison, not a substitute for confirming the specifics with your local planning department.