Quick answer: In the City of Los Angeles, a detached ADU floor plan can be up to 1,200 square feet and two stories under the City’s ADU ordinance, or up to 800 square feet at 16 feet under the state’s guaranteed “State ADU” path. An attached ADU is generally capped at 50% of the existing house, and a junior ADU (JADU) at 500 square feet inside the house. Two size lines matter as much as the layout: at 750 square feet or less no impact fees can be charged, and under 500 square feet no school fees. APLA Construction (CA Lic #1136359) designs and builds ADUs throughout Greater Los Angeles.
Choosing a floor plan is really two decisions. The first is legal: which type of ADU fits your lot and how large the City allows it to be. The second is practical: how many bedrooms, where the entry and kitchen go, and whether the unit is for a tenant, a family member or a home office. This guide covers the legal limits first, because they decide which layouts are on the table, then the common layouts and the pre-approved plan programs that can shorten design and plan check.
| ADU type | Maximum size (City of LA) | Height / stories | Notes |
|---|---|---|---|
| Detached — City ordinance ADU | 1,200 sq ft | Up to 2 stories, within the zone’s height limit | LAMC § 12.22 A.33; the usual route for a full one- or two-bedroom backyard home |
| Detached — “State ADU” | 800 sq ft | 16 ft (18 ft within ½ mile of major transit, plus 2 ft for a roof pitch matching the house) | Gov. Code § 66323(a)(2): must be approved ministerially with 4-ft side and rear setbacks |
| Attached ADU | 50% of the existing house | Cities must allow at least 25 ft or the zone limit, whichever is lower (up to 2 stories) | An attached ADU under 850 sq ft (under 1,000 sq ft with more than one bedroom) may exceed the 50% limit |
| Conversion (garage or existing space) | Existing footprint + up to 150 sq ft for entry/exit | Existing structure | Gov. Code § 66323(a)(1); no new setbacks for the existing structure |
| Junior ADU (JADU) | 500 sq ft | Inside the house | Gov. Code § 66313(d); may share a bathroom with the house |
Size is measured as the building code’s gross floor area: everything inside the exterior walls, without deducting closets, stairs or interior walls (ZA Memo 143, Q.3). A plan that “feels” like 750 square feet of living space can measure larger than that on the permit drawings.
Not exactly. State law sets minimums that cities must allow: a city cannot set a maximum ADU size below 850 square feet, or 1,000 square feet for an ADU with more than one bedroom (Gov. Code § 66321(b)(2)). The 1,200-square-foot detached limit and the 50% attached limit are the state’s default standards, and HCD’s ADU Handbook confirms a city can adopt a less restrictive ordinance that allows larger units. The City of Los Angeles uses 1,200 square feet for a detached ordinance ADU; other cities in the county set their own limits, so check the city your lot is in.
Two size thresholds in state law can change a budget more than any finish choice, so they belong in the floor-plan decision rather than after it:
These limits do not cover plan-check and building permit fees. Our ADU cost guide shows how size and type change a Los Angeles ADU budget, and our utility connections guide covers the connection charges in detail.
For a rental unit, a private entrance away from the main house, in-unit laundry, a full kitchen and good storage matter more than extra square footage. Bedrooms need code-compliant emergency escape openings, and the unit must meet California’s Title 24 energy standards. If you are weighing a separate unit against space inside the house, our ADU vs. JADU guide compares the two.
Pre-approved plans can save design time and shorten plan check, but they are not the same everywhere:
Comparing a catalog design with a custom plan? Our prefab vs. stick-built ADU guide covers the trade-offs.
On small lots in Venice, Silver Lake and Atwater Village, compact studios, attached units and two-story ordinance ADUs make the most of the space. On larger San Fernando Valley lots in Northridge, Reseda and Woodland Hills, single-story one- and two-bedroom plans are common. We match the plan to your lot, your zone’s height limit and the setbacks that apply.
In the City of Los Angeles, a detached ADU under the City’s ordinance can be up to 1,200 square feet and two stories, and a detached “State ADU” up to 800 square feet at 16 feet (18 feet near major transit). An attached ADU is generally limited to 50% of the existing house, and a junior ADU to 500 square feet inside the house.
The one-bedroom detached ADU of about 500–750 square feet. It works for most renters, and at 750 square feet or less no impact fees can be charged on it.
No. Government Code § 66311.5(c)(1) bars impact fees on an ADU with 750 square feet of interior livable space or less. Plan-check and building permit fees still apply, and a new detached ADU can still be charged a proportionate utility connection fee.
Yes. LADBS keeps a catalog of pre-approved standard plans, but they are sold by their designers rather than free, and LADBS still reviews your specific lot before issuing a permit. In unincorporated LA County, the County’s Plans A, B and C are free.
Yes. A custom plan is drawn around your lot, setbacks and goals. Pre-approved plans may or may not allow changes, so check with the designer before buying one.
APLA Construction designs and builds ADU floor plans across Los Angeles. Licensed CA Lic #1136359 — verify on CSLB. Call (818) 818-4419 or email info@aplaconstruction.com for a free ADU consultation.
Sources, read October 2026: California Government Code § 66313, § 66314, § 66321, § 66323 and § 66311.5; Education Code § 17620; HCD Accessory Dwelling Unit Handbook; Los Angeles City Planning ZA Memorandum No. 143, Revision 1 (Aug. 1, 2025); LADBS ADU page and Standard Plan Program; LA County Planning Standard ADU Plans. Rules vary by city and change often, so confirm your lot’s limits before design. General information, not legal advice.