The five ADU types at a glance
| Type | Best for | Typical construction cost | Est. rent | Value added |
|---|---|---|---|---|
| Detached ADU | Maximum design freedom & rental flexibility | $170K–$420K+ | $1.8K–$2.8K/mo | $160K–$320K+ |
| Attached ADU | Multigenerational living, some independence | $140K–$280K | $1.6K–$2.2K/mo | $120K–$220K |
| Garage Conversion | A popular, lower-cost entry point | $115K–$210K | $1.3K–$1.9K/mo | $90K–$170K |
| Junior ADU (JADU) | Lowest-cost entry, fastest path | $70K–$140K | $1.1K–$1.7K/mo | $50K–$90K |
| Prefab / Modular | Faster, factory-built timelines | Varies by model | Comparable to detached | Varies |
Cost, rent, and value-added ranges are general market estimates for planning purposes only — not quotes, appraisals, or guarantees. Actual figures depend on your property, market conditions, finish level, site conditions, and financing. A licensed contractor, appraiser, or lender can give you numbers specific to your project.
Explore each type in detail
How to choose the right type
ADU types: common questions
An ADU is a fully independent second home — its own kitchen, bathroom, and entrance. A Junior ADU (JADU) is created within the walls of your existing house, capped at 500 sq ft, with more relaxed kitchen requirements but often a shared bath and an owner-occupancy rule. JADUs are usually the cheapest and fastest path; a detached ADU offers the most independence. Specifics vary by city, so confirm the rules for your address.
Generally a Junior ADU or a garage conversion, because they reuse existing structure instead of building new from the ground up. A new detached unit is typically the most expensive. The ranges on this page are planning estimates only — see the full cost breakdown for what actually moves the number.
Often a well-built detached unit, because it adds the most independent, rentable square footage — but the value any ADU adds depends heavily on your property, the finish level, and local comparable sales. It's a general pattern, not a guarantee. Our guide on whether an ADU increases property value goes deeper.
Often, yes. California rules frequently allow a single-family lot to add both a detached ADU and a Junior ADU, and multifamily properties may qualify for more. Exactly what your lot allows depends on your city and property, so confirm with your city or start with a free property review for a read on your specific situation.
Detached units generally command the highest rent and offer the most flexibility, but a garage conversion can be a strong lower-cost entry point with a faster path to a tenant. The best choice balances your lot, your budget, and the rent comparable units actually earn near you — see the rental income guide.