How tall can an ADU be in Los Angeles, and can it be two stories?

What is the height limit for a backyard ADU in Los Angeles?

The answer depends on which of two rule books you build under. State law sets floors that no city can go below: 16 feet for a detached ADU on a lot with a house or apartment building ¹, 18 feet if the lot is within half a mile walking distance of a major transit stop or high-quality transit corridor ², and 2 more feet on top of that when the ADU roof pitch matches the main house ³. A detached ADU on a lot with an existing or proposed multifamily, multistory building also gets 18 feet ²¹.

Los Angeles applies those numbers to its State ADU, the detached new building of up to 800 square feet with 4-foot side and rear setbacks ¹⁴. City Planning's ADU table lists that type at 16 feet, or 18 feet within half a mile of transit, plus 2 more feet for a matching roof pitch, for 20 feet total ⁸.

The second rule book is the City's own ADU ordinance. Its detached ADU, which can be larger than 800 square feet, is limited to 2 stories, not counting basements, and to the zone's height limit for a new building or addition ⁸.

• State detached ADU (up to 800 sq ft): 16, 18 or 20 feet ⁸.
• City ordinance detached ADU: 2 stories and the zoning height limit ⁸.
• Attached ADU: the zoning height limit or 25 feet, whichever is lower ⁹.
• Conversion of an existing garage or shed: the height of the building you already have ⁶.

Does my lot qualify for 18 or 20 feet?

Only if you can show that the lot is within half a mile walking distance of a major transit stop or a high-quality transit corridor ². City Planning explains that the height incentive requires a bus line with 15-minute headways during peak periods, and that you can prove it by printing Section C of the SB 9 Eligibility viewer on ZIMAS, under the Planning and Zoning tab ¹². The state's handbook also points to the California State Geoportal map for checking whether an address is in a High-Quality Transit Corridor ⁷.

The extra 2 feet, from 18 to 20, depend on the roof. City Planning counts the ADU roof as aligned with the house when the roof slope percentage is the same, and a flat roof of 2% or less is not considered to have a pitch at all ¹¹. If your house has more than one roof pitch, the ADU only has to match one of them, but the entire ADU roof must match it ¹¹. A flat-roofed modern ADU behind a pitched-roof ranch house does not get the extra 2 feet.

Can I build a two-story ADU in Los Angeles?

Yes. There are two ways to get there. Under the City ordinance, a new detached ADU can be up to 2 stories and as tall as the zone allows ⁸. On a lot zoned R1, RS or RE9, LADBS limits buildings to 28 feet when any part of the roof slopes less than 25%, and 33 feet when the slope is 25% or more ¹⁵. On larger RA and RE11 through RE40 lots the limits are 30 and 36 feet ¹⁶. Either way, there is room for two stories.

Under state law, a two-story ADU is also protected if it fits. The state housing department says that if a detached two-story ADU can be built within the state height allowances and still meet the building code, a city cannot deny it, even where zoning limits the main house to one story ⁵. In practice, fitting two stories under a 16-foot roof is tight, which is why most two-story backyard houses in Los Angeles go the ordinance route.

The ordinance route carries trade-offs that the State ADU does not. On any lot that is both in a Very High Fire Hazard Severity Zone and in a Hillside Area, the ordinance prohibits ADUs unless a few listed exceptions apply ¹³. That restriction is why a two-story plan for a foothill lot can be unbuildable while an 800 square foot one-story plan on the same lot is fine. Our fire zone guide walks through that case, and the setbacks guide covers where a taller building can sit.

How tall can an attached ADU or an ADU over my garage be?

An attached ADU can be as tall as the zoning height limit for the house or 25 feet, whichever is lower ⁴⁹. On an R1 lot, where the house limit is 28 or 33 feet ¹⁵, that means 25 feet in practice. State law does not require a city to allow an attached ADU above two stories ⁴.

A conversion is different. When you turn an existing garage or shed into an ADU, the state handbook says the height is limited to the dimension of the original structure ⁶. You may add up to 150 square feet beyond the old footprint only for getting in and out, and the handbook gives a staircase to a second-story ADU as the example ²⁰. Adding a whole new floor on top of a detached garage is an addition, which in Los Angeles falls under the ordinance's 2-story and zoning height limit ⁸.

Before you plan anything on top of a garage, confirm the garage itself is on record. Our garage permit guide shows how to look it up.

How does the city measure the height of an ADU?

Los Angeles measures an ADU the same way it measures any other building, under the height rules of the zone, the Height District, any Hillside Area, Specific Plan or other overlay ¹⁰.

On a flat Valley lot, LADBS defines height as the distance from grade to the highest point of the building, including parapets, and defines grade as the lowest point of the finished ground, paving or sidewalk within 5 feet around the building ¹⁷. That detail matters. If your backyard drops a foot toward the back fence, the lowest point next to the ADU is where the measurement starts, and a 16-foot roof drawn from the high side can come out over the limit.

The ADU plan check correction sheet asks for a topographic map with the building outlined to determine its height ¹⁹. Hillside Areas follow their own height rules, which is one more reason to check your lot's overlays before you choose a design ¹⁰.

How do I find out which height limit applies to my lot?

You can work most of it out yourself with public tools.

1. Look up your address on ZIMAS and note the zone, for example R1-1, and whether the parcel is in a Hillside Area, a Very High Fire Hazard Severity Zone or a Specific Plan. Each can change the limit ¹⁰¹³.
2. Read the zone against the LADBS limits: 28 or 33 feet for R1, RS and RE9, and 30 or 36 feet for RA and RE11 through RE40, depending on roof slope ¹⁵¹⁶. A variation zone such as R1V has its own number ¹⁸.
3. Open the SB 9 Eligibility viewer in ZIMAS and print Section C to see whether you qualify for the transit height ¹².
4. Decide your path. A one-story backyard house of up to 800 square feet fits the State ADU at 16 to 20 feet ⁸. A larger or two-story one needs the ordinance path and the zone limit ⁸.
5. Measure the fall of your yard. On a sloped yard the lowest point within 5 feet of the ADU sets the starting line ¹⁷.

This is the kind of question a lot check settles, because the answer comes from the zone, the overlays and the ground together. For what fits on a typical Valley lot, see what size ADU fits on a 6,600 square foot lot.

Quick answers

Sources

1. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-09
2. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-09
3. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-09
4. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-09
5. Accessory Dwelling Unit Handbook, California Department of Housing and Community Development (HCD). Facts checked 2026-10-09
6. Accessory Dwelling Unit Handbook, California Department of Housing and Community Development (HCD). Facts checked 2026-10-09
7. Accessory Dwelling Unit Handbook, California Department of Housing and Community Development (HCD). Facts checked 2026-10-09
8. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
9. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
10. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
11. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
12. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
13. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
14. ZA Memo 143, Revision 1: Accessory Dwelling Units (LAMC Chapter 1), Los Angeles City Planning, Office of Zoning Administration. Facts checked 2026-10-09
15. Plan Check Zoning Correction Sheet, Single-Family Zones (Mansionization), LADBS. Facts checked 2026-10-09
16. Plan Check Zoning Correction Sheet, Single-Family Zones (Mansionization), LADBS. Facts checked 2026-10-09
17. Plan Check Zoning Correction Sheet, Single-Family Zones (Mansionization), LADBS. Facts checked 2026-10-09
18. Plan Check Zoning Correction Sheet, Single-Family Zones (Mansionization), LADBS. Facts checked 2026-10-09
19. ADU Plan Check Correction Sheet, LADBS. Facts checked 2026-10-09
20. Accessory Dwelling Unit Handbook, California Department of Housing and Community Development (HCD). Facts checked 2026-10-09
21. California Government Code § 66321 (mirror of the official text), California Legislature, via Public.Law. Facts checked 2026-10-09

Greenlight is not a contractor, architect or engineer, and this is not legal advice. Rules change; every fact here shows the date we last checked it.