ADU Laws · 2026
How Big Can an ADU Be in California? (2026 Size Limits)
In California, a detached new-construction ADU can be built up to 1,200 square feet, and state law forces every city to allow at least an 800 sq ft ADU (up to 16 feet tall) regardless of what local rules say. So the practical answer for most homeowners is simple: you can build somewhere between a small studio and a roughly 1,200 sq ft two-bedroom, and your city cannot stop you from building at least 800 sq ft.
Below we break down every size rule that applies in 2026: detached vs. attached ADUs, the 800 sq ft floor, Junior ADUs (JADUs), and how our 14 models (405 to 1,200 sq ft) map cleanly onto the law.
The short version: Detached ADU = up to 1,200 sq ft. Cities must allow at least 800 sq ft / 16 ft no matter what. Attached ADU = up to 50% of your main house (with the same 800 sq ft floor). JADU = up to 500 sq ft inside the existing home. State law sets these minimums and local cities cannot undercut them.
The maximum size: 1,200 sq ft detached
California’s statewide ADU law (Government Code §65852.2) sets a hard ceiling of 1,200 square feet for a detached, new-construction ADU. That is the largest standalone backyard home the state requires cities to permit by right.
A city is allowed to set its own size cap above the state floor, but it can never push the number down below the protections the state guarantees. In plain terms: your city can be more generous, but it cannot be stingier than the law.
The 800 sq ft floor every city must allow
This is the rule that protects homeowners the most. No matter what a local zoning ordinance says about lot coverage, floor-area ratio, or open-space requirements, your city must allow you to build an ADU that is at least:
- 800 square feet of floor area, and
- 16 feet in height (taller in some transit-rich areas), with
- 4-foot side and rear setbacks
If a city tried to use its own rules to deny an 800 sq ft ADU on a normal single-family lot, those rules are preempted by state law. That is why “my lot is too small” is far less common than people fear. You can confirm exactly what your lot supports in a free feasibility study.
Attached ADUs are sized differently
If you attach the ADU to your existing house (sharing a wall) rather than building it detached in the yard, the math changes. An attached ADU can be built up to 50% of the existing primary home’s floor area, but the 800 sq ft floor still applies. So:
- If your main house is 2,000 sq ft, a 50% attached ADU could be up to 1,000 sq ft.
- If your main house is only 1,200 sq ft, 50% would be 600 sq ft, but the state still lets you build up to 800 sq ft because the floor wins.
Most of the homes we build are detached, factory-built units that arrive ~97% complete and get crane-set in the backyard, so the 1,200 sq ft detached ceiling is the number that matters for the majority of our customers.
JADUs: the 500 sq ft option inside your home
A Junior ADU (JADU) is a separate, smaller category. A JADU is carved out of the existing walls of your single-family home (often a converted bedroom or attached garage area), and it is capped at 500 square feet. Key differences:
- It must be created within the existing footprint of the home.
- It requires owner-occupancy (you, or your tenant in the main house, must live on the property).
- It may share a bathroom with the main house.
A single-family lot can generally have all three at once: the primary home + one ADU + one JADU. That is a powerful combination for housing family. For a deeper comparison, see our guide on JADU vs. ADU.
California ADU size limits at a glance (2026)
| ADU type | Maximum size | Minimum the city must allow | Notes |
|---|---|---|---|
| Detached, new construction | 1,200 sq ft | 800 sq ft / 16 ft | The most common backyard home |
| Attached to main house | 50% of primary home’s floor area | 800 sq ft | Shares a wall with existing house |
| Conversion (within existing structure) | Size of the existing space | n/a | No setback required within the footprint |
| JADU (Junior ADU) | 500 sq ft | n/a | Inside existing home, owner-occupancy required |
Local specifics (exact height bonuses near transit, lot-coverage details) vary by city and are confirmed in your free feasibility study.
How our 14 models map onto the size limits
Our lineup is built to fit comfortably inside the law, from a compact studio to a full two-bedroom right at the detached ceiling. Every model’s price includes a permitting budget along with plans, foundation, factory build, delivery, hookups, appliances, and final inspection, and pricing runs from $180,000 to $557,000 depending on size, layout, and finish style. Exact permit costs are set by your city and confirmed in your feasibility study.
| Size range | What it fits | Where it lands in the law |
|---|---|---|
| 405 to 600 sq ft | Studio / 1-bed | Well under every city’s 800 sq ft floor |
| 600 to 800 sq ft | 1-bed, impact-fee friendly | At or under the protected 800 sq ft minimum |
| 800 to 1,000 sq ft | 1 to 2 bed | Above the floor, under the 1,200 ceiling |
| 1,000 to 1,200 sq ft | Full 2-bed | Right at the detached maximum |
Two size-related money notes worth knowing:
- Impact fees are waived for any ADU under 750 sq ft. That is one reason our smaller models are so popular, you skip a category of fees entirely.
- Larger ADUs (750 sq ft and up) pay impact fees proportionally, charged based on size. This is one of the line items your feasibility study spells out for your specific city.
You can browse the full lineup on our models page, compare totals on the pricing page, or estimate your project with the ADU calculator. Each model comes in three styles: Classic Craftsman (standard), Urban Farmhouse, and Ultra Modern.
Frequently asked questions
Can I build a 1,200 sq ft ADU on a small lot?
In most cases, yes. State law guarantees you at least 800 sq ft with 4-foot setbacks regardless of lot size, and many normal lots can fit the full 1,200 sq ft detached unit. The real limiter is usually setbacks and existing structures, not a city size cap. The only way to know your exact buildable footprint is a property analysis, which is what the free feasibility study provides.
Does a bigger ADU mean a longer build?
Not dramatically. Because we build ~97% of the home in our Salinas factory while your foundation and permits move in parallel, both a 500 sq ft studio and a 1,200 sq ft two-bedroom are delivered in roughly 4 to 9 months. Size affects the price more than the timeline. See how that works on our process page.
Is there a minimum size for an ADU?
There is no statewide minimum square footage, but an ADU must include the basics of independent living: a kitchen, a bathroom, and a place to sleep. Our smallest model is 405 sq ft, which comfortably delivers a complete, livable home.
Do I have to live on the property to build a 1,200 sq ft ADU?
No. California has suspended the owner-occupancy requirement for standard ADUs, so you can build and rent out a full-size ADU without living on site. Owner-occupancy still applies to JADUs (the 500 sq ft in-home option). Our guide on California ADU rental laws covers this in detail.
Can I build more than one ADU?
On a single-family lot, you can generally have your primary home plus one ADU and one JADU. Multifamily properties allow more units. The combination of a 1,200 sq ft ADU and a 500 sq ft JADU is a popular way to house extended family or add two income streams on one lot.
Wondering exactly how big an ADU your specific lot can hold, and roughly what it would cost, permitting budget included? Our team will analyze your property, setbacks, and city rules for you. Start your feasibility study and we’ll show you the largest ADU your lot supports, with a clear total price and timeline.