Can I build an ADU if my Los Angeles lot is in a Hillside Area?

How do I know if my lot is in a Hillside Area?

Look up your address in ZIMAS and read the Hillside Area row in the parcel report. A Hillside Area is any area shown on the city's Hillside Area Map, so the answer is a line on a map, not how steep your yard looks ¹.

In the Valley that line follows the foothills. We checked every City of Los Angeles single-family parcel in 35 Valley ZIP codes against the city's published Hillside Area layer, using the center point of each parcel ²:

• Woodland Hills 91364: 5,743 of 7,780 homes, 74%.
• Porter Ranch 91326: 3,859 of 6,545, 59%.
• Encino 91436: 2,738 of 4,859, 56%.
• Tarzana 91356: 2,960 of 5,449, 54%.
• Sherman Oaks 91403: 2,285 of 4,207, 54%.
• Studio City 91604: 2,932 of 5,837, 50%.
• Granada Hills 91344: 3,833 of 13,337, 29%.
• Reseda, Van Nuys, Lake Balboa, North Hollywood, Winnetka, Panorama City and Northridge 91324: none.

A lot near the edge of the line can fall on either side, so the ZIMAS row for your own parcel is the answer that counts.

Can I build an ADU on a hillside lot that is not in a fire zone?

Yes. The city's ban reaches only lots that are in both a Hillside Area and a Very High Fire Hazard Severity Zone, so a hillside lot outside the fire zone can take either a state-law ADU or one of the city's own Ordinance ADUs ³.

The two paths treat the hillside very differently. State-law ADUs, such as a detached backyard house up to 800 square feet, a garage conversion or a junior ADU, are exempt from local zoning, design and development standards ⁴. The city's Ordinance ADUs follow the city's rules, and on a hillside those include the hillside height rules and the hillside floor-area limit ⁵⁶. The fire-zone guide lays the two paths side by side, and the height guide covers how tall each one can be.

Hillside-only lots are not the usual case. In Woodland Hills 91364, Encino 91436, Tarzana, Sherman Oaks 91403 and Studio City, nearly every hillside home in our count is also in the fire zone ². The hillside-only lots cluster in Granada Hills, where 3,833 homes are in the Hillside Area but only 1,781 of them are also in the fire zone, and to a lesser degree in Porter Ranch, Sylmar and Canoga Park 91304 ².

Will the Baseline Hillside Ordinance shrink my ADU?

Not a state-law ADU. City Planning says the residential floor area limit, called RFA, may not be enforced on state-law ADUs, and may not push any ADU below the sizes state law protects: 800 square feet detached, and 850 or 1,000 square feet attached ⁵.

For an Ordinance ADU, RFA in the R1, RE, RS and RA zones can limit the size further ⁵. On a hillside lot that limit comes from the Baseline Hillside Ordinance. The LADBS ADU correction sheet tells applicants to get a Joint Referral Form from City Planning to set the maximum RFA, with a slope analysis map that becomes part of the approved plans, and it can flag a project that exceeds the maximum RFA or the maximum cubic yards of grading ⁷.

In practice, a larger Ordinance ADU on a hillside lot shares one floor-area budget with the main house. If the house already uses most of it, the 800-square-foot state-law backyard house is the option that limit cannot touch ⁵.

Will the city make me widen the street in front of my hillside lot?

Generally no. City Planning's guidance says no physical public improvements or dedication may be required for any type of ADU or junior ADU, and it names the hillside street access rule, LAMC 12.21 C.10(i), among the requirements that do not apply ⁸.

The exception is narrow. An Ordinance ADU on a lot that is in both a Hillside Area and the fire zone can still be required to make dedications, and may be asked for public improvements toward a 20-foot-wide street frontage ⁸.

You may still see the street question in plan check. The LADBS ADU correction sheet, last revised in 2021, has an item saying the Hillside Ordinance may apply and asking for a determination from Public Works of whether the street is standard or substandard ⁷. City Planning's guidance is the newer document, issued in August 2025, so it is worth knowing it exists if a narrow street is the only thing in question ⁸.

What changes if my hillside lot is also in the fire zone?

Then the both-zones rule applies. State-law ADUs stay available, and the city's larger Ordinance ADU is the one that is restricted ³. The fire-zone guide covers that rule in detail, so here are the three points it does not.

1. The rule lands mostly on the Valley. A council motion in April 2024 described how the city exempted two east-side community plan areas, Northeast Los Angeles and Silver Lake–Echo Park–Elysian Valley, so the standards apply in West Los Angeles and the San Fernando Valley ⁹. The motion asked for that exemption to be repealed; we did not find a record of the outcome as of October 2026.
2. The old conditions have been cut back. The 2019 ordinance allowed ADUs in these areas only with an automatic sprinkler system, one off-street parking space and roadway improvements of at least 20 feet in front of the lot ¹⁰. City Planning now says the city may not impose the sprinkler and parking conditions on Ordinance ADUs where they conflict with state law, and the street condition is limited to dedications and frontage improvements ¹¹⁸.
3. Some fire-zone neighborhoods are outside the Hillside Area altogether. West Hills 91307 has 1,913 single-family homes in the fire zone in our count, and Woodland Hills 91367 has 1,900, yet almost none are in the Hillside Area ². LADBS permit records agree: no permit in 91307 and only 6 in 91367 carry the Hillside flag ¹³. On those lots the both-zones ban does not reach an Ordinance ADU at all ³.

What does a hillside lot add to my plans and permits?

Mostly soil and grading review, and often a slower plan check. LADBS says permits are required for grading or earthwork in the Hillside Grading Area, and that a soils and/or geology report is usually required before those permits issue ¹². Basement and pool excavations in a Hillside area need a grading plan check before any permit is issued ¹⁴.

The state-law exemption covers zoning, design and development standards ⁴. It is not a pass on building review: the ADU correction sheet still asks for soil, foundation and geology reports approved by the LADBS Grading Section where they apply ¹⁵.

The soils report guide explains when the grading pre-inspection asks for a report and what one costs, and the plan check guide shows why a one-story ADU outside the hillside rules tends to move faster. Knowing which of these rules reach your parcel before anyone draws plans is the kind of thing a lot check settles.

Quick answers

Sources

1. Zoning Code glossary: Hillside Area, Los Angeles City Planning. Facts checked 2026-10-10
2. Greenlight parcel count: LA County Assessor single-family parcels (City of LA, 35 Valley ZIPs) matched to the City of LA GeoHub "Hillside Ordinance" (Hillside Area) and "Very High Fire Hazard Severity Zones" layers, City of Los Angeles GeoHub / LA County Assessor parcel layer (Greenlight analysis). Facts checked 2026-10-10
3. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.42, Los Angeles City Planning / LADBS. Facts checked 2026-10-10
4. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, section on GC § 66323(a), Los Angeles City Planning / LADBS. Facts checked 2026-10-10
5. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.3, Los Angeles City Planning / LADBS. Facts checked 2026-10-10
6. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.5, Los Angeles City Planning / LADBS. Facts checked 2026-10-10
7. Accessory Dwelling Unit Plan Check Correction Sheet (PC/STR/Corr.Lst.20A1, Rev. 8/03/2021), items 26 to 28, Los Angeles Department of Building and Safety (LADBS). Facts checked 2026-10-10
8. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.32, Los Angeles City Planning / LADBS. Facts checked 2026-10-10
9. Motion (Hernandez), Council File 16-1468-S2, Apr. 26, 2024, Los Angeles City Council / City Clerk. Facts checked 2026-10-10
10. Motion (Hernandez), Council File 16-1468-S2, Apr. 26, 2024 (on Ordinance 186481), Los Angeles City Council / City Clerk. Facts checked 2026-10-10
11. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.42 (Ordinance ADUs), Los Angeles City Planning / LADBS. Facts checked 2026-10-10
12. Grading Inspections, Los Angeles Department of Building and Safety (LADBS). Facts checked 2026-10-10
13. Building and Safety - Building Permits Issued from 2020 to Present (N), dataset pi9x-tg5x (Greenlight query, Hillside Ordinance Area flag by ZIP), City of Los Angeles Open Data / LADBS. Facts checked 2026-10-10
14. Grading Permits, Los Angeles Department of Building and Safety (LADBS). Facts checked 2026-10-10
15. Accessory Dwelling Unit Plan Check Correction Sheet (PC/STR/Corr.Lst.20A1, Rev. 8/03/2021), item B.5, Los Angeles Department of Building and Safety (LADBS). Facts checked 2026-10-10

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.