Can I build an ADU in Chatsworth (91311) or Porter Ranch (91326)?

Can I build an ADU on my Chatsworth or Porter Ranch lot?

Almost certainly some kind of ADU, yes. Los Angeles allows ADUs in any zone where a house is a permitted use ⁶. We matched every single-family parcel in both ZIPs to the city's zoning map. In Chatsworth 91311, 2,429 of 6,827 parcels are zoned RS, 1,746 RA, 1,724 RE and 792 R1. In Porter Ranch 91326, 4,402 of 6,545 are zoned RE, 1,671 RS and 446 RA ⁵.

State law guarantees three kinds of ADU that the city has to approve on a single-family lot:

• A detached backyard house of up to 800 square feet, with four-foot side and rear setbacks, which can be paired with a JADU ⁷.
• A garage conversion or conversion of another existing accessory building, which can grow by up to 150 square feet only to fit an entry or exit ⁸.
• A junior ADU (JADU) of no more than 500 square feet, inside the house ⁹.

The city's own ADU ordinance adds a larger detached unit of up to 1,200 square feet and two stories ¹⁰. Here, whether that bigger option is open depends mostly on the fire and hillside maps below. Our JADU vs ADU guide compares the smaller choices.

How big are lots in Chatsworth and Porter Ranch?

Bigger than most of the Valley, in two different patterns. In Chatsworth the middle single-family lot is 9,829 square feet, a quarter are under 7,560 and a quarter are over 16,298 square feet, so the range runs from ordinary tract lots to large RA parcels ². In Porter Ranch the middle lot is 10,999 square feet and the middle half all fall between 8,940 and 11,881 square feet, a much tighter range ². For comparison, the middle lot in Reseda 91335 is 6,639 square feet ².

On lots this size there is usually room in the yard for an 800-square-foot backyard house with four-foot side and rear setbacks ⁷. Our setbacks guide covers the distances.

Chatsworth also has horse property. By our count, 299 Chatsworth single-family parcels, about 4%, are in a "K" Equinekeeping District, most of them zoned RA-1-K; Porter Ranch has none ⁵. City Planning says ADUs and JADUs are exempt from the city's distance rules between horse enclosures and homes ¹⁸. Our Sylmar guide explains what that means for you and for a neighbor who keeps horses.

Is my Chatsworth or Porter Ranch lot in a fire zone or a Hillside Area?

In Porter Ranch, more likely than not; in Chatsworth, about one lot in five. We tested every single-family parcel against the city's map layers. In Chatsworth, 1,247 of 6,827 parcels (18%) are in the Very High Fire Hazard Severity Zone and 632 (9%) are in a Hillside Area. In Porter Ranch, 3,562 of 6,545 parcels (54%) are in the fire zone and 3,859 (59%) are in a Hillside Area ³⁴.

A fire zone on its own does not stop an ADU. The state housing department (HCD) says the fire hazard maps are meant to govern building materials and defensible space around structures, not to restrict housing, and that a fire hazard zone is not by itself a conclusive reason to restrict ADUs ¹⁴. What the fire zone changes is how you build. Our fire zone guide covers materials, and our fire sprinklers guide covers when sprinklers come in.

Treat our fire-zone counts as a floor. The city map layer we used was last edited in 2019. CAL FIRE issued new recommended fire hazard maps for Los Angeles on March 24, 2025, the Fire Department said it expected more parcels to be affected, and state law requires the city to adopt those maps by ordinance ³¹³.

My Porter Ranch lot is in both zones. What can I still build?

You can still build a state-law ADU; what gets hard is the city's bigger 1,200-square-foot unit. The city code bars ADUs on lots in both a Very High Fire Hazard Severity Zone and a Hillside Area except in a few listed cases, but City Planning says that bar may not be enforced on state-law ADUs ¹¹. By our count, 3,394 Porter Ranch single-family parcels, about 52%, sit in both zones, compared with 508 in Chatsworth, about 7% ⁴.

So on most of those lots the dependable menu is an 800-square-foot backyard house, a garage conversion or a JADU ⁷⁸⁹¹¹. The street in front can matter as well. City Planning says that, generally, no street widening or dedication can be required for any ADU, but an Ordinance ADU on a lot in both zones may have to make public improvements to meet a 20-foot-wide street frontage rule ¹².

Our Hillside Area guide covers slope, grading and street width, and our 150-foot access guide covers fire access.

My HOA has CC&Rs. Can the HOA stop my ADU?

Not outright. HCD says Sections 714.3 and 4751 of the California Civil Code make CC&Rs and operating rules that effectively prohibit or unreasonably restrict an ADU or JADU on a single-family lot void and unenforceable ¹⁵. That applies to the master-planned tracts in Porter Ranch the same as anywhere else in the state.

An HOA can still review your design. HCD says it may set limited objective standards, such as specific materials, architectural styles and other design rules, within reason. Those standards cannot be stricter than state ADU law in a way that unreasonably raises the cost or blocks the unit, and they cannot include fees or other financial requirements ¹⁶. HCD lists examples of what crosses the line, including:

• A slow review: any delay beyond the 60 days a city gets, or one that significantly delays the ADU ¹⁷.
• A neighbor veto: requiring neighboring owners to approve or agree to the ADU ¹⁷.

Send the association your plans while the city reviews them, so the two reviews run side by side. If your CC&Rs ban ADUs outright, HCD encourages owners to contact their local agency ¹⁵.

Are my neighbors actually getting ADU permits?

Yes, though at a slower pace than the flat Valley. LADBS issued 35 ADU and JADU building permits in Chatsworth 91311 in 2023, 38 in 2024, 54 in 2025 and 39 in 2026 through Oct. 3. In Porter Ranch 91326 the counts were 15, 22, 34 and 27 ¹. These are permits, not units, because one project can carry more than one permit.

Per home, both ZIPs build far less than the Valley floor. In 2025 the city issued about 8 ADU permits for every 1,000 single-family parcels in Chatsworth and about 5 in Porter Ranch, compared with about 23 in Reseda 91335 ¹². Our Valley permits by ZIP guide has the full ranking.

What should I look up first for my address?

Start with the city's free parcel report. Look up your address in ZIMAS, the city's mapping system for a parcel's zoning and permit history ¹⁹, and write down these items:

1. The full zone string. A zone such as RA-1-K tells you the base zone and whether you are in a K horsekeeping district ⁵.
2. The fire zone and Hillside Area rows. Both together limit the 1,200-square-foot Ordinance ADU; either one changes how you build ¹¹.
3. Lot size. Compare it with the ranges above to see whether a bigger unit is worth sketching ².
4. Your CC&Rs, if you are in an HOA. Find the architectural review rules and how long the association takes to answer ¹⁶¹⁷.

Then look at what ZIMAS does not settle: how far the sewer main is from your lot (sewer guide), whether a large tree is in the way (protected trees guide), and whether slope or soil calls for a soils report. Putting those answers together for one address is the kind of thing a lot check settles. If you live just south or east, see our guides for Canoga Park and West Hills, Woodland Hills and Northridge.

Quick answers

Sources

1. Building Permits Issued from 2020 to Present (N), dataset pi9x-tg5x, ZIPs 91311 and 91326 with Reseda 91335 for comparison, LADBS via City of Los Angeles Open Data (Greenlight query). Facts checked 2026-10-12
2. LA County Assessor parcel layer (LACounty_Parcel), single-family parcels in ZIPs 91311 and 91326, City of Los Angeles, LA County Assessor (Greenlight analysis). Facts checked 2026-10-12
3. Greenlight parcel count: City of LA single-family parcels in ZIPs 91311 and 91326 tested against the City of LA Very High Fire Hazard Severity Zones layer, LA County Assessor parcel layer / City of Los Angeles GeoHub (Greenlight analysis). Facts checked 2026-10-12
4. Greenlight parcel count: City of LA single-family parcels in ZIPs 91311 and 91326 tested against the Hillside Area and Very High Fire Hazard Severity Zone layers, LA County Assessor parcel layer / City of Los Angeles GeoHub (Greenlight analysis). Facts checked 2026-10-12
5. Greenlight parcel count: City of LA single-family parcels in ZIPs 91311 and 91326 by zone, from the City Planning zoning layer, LA County Assessor parcel layer / City of Los Angeles GeoHub, City Planning zoning (Greenlight analysis). Facts checked 2026-10-12
6. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Q.2, Los Angeles City Planning / LADBS. Facts checked 2026-10-12
7. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, quoting Gov. Code § 66323(a)(2), Los Angeles City Planning / LADBS. Facts checked 2026-10-12
8. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, on Gov. Code § 66323(a)(1), Los Angeles City Planning / LADBS. Facts checked 2026-10-12
9. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, section B (JADUs), Los Angeles City Planning / LADBS. Facts checked 2026-10-12
10. ZA Memorandum No. 143, Revision 1 (LAMC Chapter 1): Implementation of the ADU Ordinance and State ADU Law, issued Aug. 1, 2025, Table 1 (detached ADUs), Ordinance ADU column, Los Angeles City Planning / LADBS. Facts checked 2026-10-12
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, Los Angeles City Planning / LADBS. Facts checked 2026-10-12
12. 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 2026-10-12
13. 2025 CAL FIRE Fire Hazard Severity Zones Map Recommendation (Apr. 4, 2025), Los Angeles Fire Department. Facts checked 2026-10-12
14. Accessory Dwelling Unit Handbook, "Can local agencies restrict ADUs based on Fire Hazard Severity Zones or other environmental hazards?", California Department of Housing and Community Development (HCD). Facts checked 2026-10-12
15. Accessory Dwelling Unit Handbook, Homeowners Associations (HOAs), on Civil Code §§ 714.3 and 4751, California Department of Housing and Community Development (HCD). Facts checked 2026-10-12
16. Accessory Dwelling Unit Handbook, Homeowners Associations (HOAs): "What restrictions can be placed on an ADU or JADU?", California Department of Housing and Community Development (HCD). Facts checked 2026-10-12
17. Accessory Dwelling Unit Handbook, Homeowners Associations (HOAs): examples of effective prohibitions, California Department of Housing and Community Development (HCD). Facts checked 2026-10-12
18. Report back on recommendations relative to equestrian uses, CF 16-1468-S4 and CF 25-0096, June 24, 2026, Impacts on Equine Distancing Requirements, Los Angeles City Planning. Facts checked 2026-10-12
19. Zoning Search (ZIMAS), Los Angeles City Planning. Facts checked 2026-10-12

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.