ADUs · garage conversions · backyard cottages
Can you build a second home on your lot?
More states now make cities allow ADUs than local codes let on. See what your state guarantees, what your city adds, and the actual permit steps and contacts.
What can I build?
ADUs, junior ADUs, garage conversions, tiny houses and lot splits, and what state law guarantees.
What will it cost, and will it pay?
Real cost figures from public studies, fees, financing, property tax and a rent payback calculator.
How do I get the permit?
The steps from zoning check to final inspection, how long the city has to decide, and who to hire.
States and cities we cover
What you can build
- What is an ADU (accessory dwelling unit)?What counts as an ADU or junior ADU, attached, detached and garage-conversion units, other names for ADUs, and states that make cities allow them.
- Converting a garage into an ADU or living spacePermits, parking rules and building code issues (egress, ceiling height, insulation, fire walls, slab) for turning a garage into an ADU or living space.
- Junior ADUs (JADUs): the small unit inside your houseWhat a California junior ADU is: the 500 sq ft limit, entrance, efficiency kitchen, bathroom, owner-occupancy and deed restriction rules, fees and permits.
- Putting a tiny house in your backyardWhen a backyard tiny house can be a legal home: foundation vs wheels, the building code's tiny house appendix, and when a tiny house counts as an ADU.
- Prefab ADUs: modular, manufactured and factory-built unitsHow prefab ADUs are regulated: HUD-code manufactured homes vs state-approved modular units, which permits you still need, and where they count as ADUs.
- SB 9: building two homes and splitting your lot in CaliforniaHow California's SB 9 works: who qualifies, lot split size rules, the owner-occupancy affidavit, what cities can deny, ADUs, and SB 684 small-lot subdivisions.
Getting it permitted
- The ADU permit process, step by stepThe usual steps to permit an ADU, from checking your lot to plan review, fees, inspections and occupancy, plus state deadlines and what slows permits down.
- Who to hire for your ADU, and how to check themWho does what on an ADU (architect, designer, engineer, contractor, prefab, expediter), state license lookups, and who should pull the permit.
Cost and money
- What does an ADU cost?Sourced ADU cost figures, the parts of the bill (design, permits, impact fees, utilities, construction) and how fee rules cut costs for small units.
- How to pay for an ADUADU financing options compared: cash-out refinance, HELOC, renovation and construction loans, counting ADU rent to qualify, and state grants and loans.
- How an ADU affects your property taxesIn California, building an ADU adds the new unit's value to your assessment; the rest of your home keeps its base year value. How it's valued and billed.
How this site works
- Every rule, fee and deadline links to the official source it came from: state statutes, state housing agencies and city code and permit pages.
- Where a city's own page looks older than a newer state law, we say so instead of guessing.
- Each page shows when we last checked it. More on how we check facts.