Same zip, different jurisdiction: this page covers LA County Public Works (DPW). The same zip code(s) also cover parts of Santa Clarita (Santa Clarita (its own permits)). Verify your parcel's jurisdiction before filing — different agencies, different rules.
Santa Clarita Valley · LA County (Unincorporated)
ADU permits in Castaic
Zip codes:91384
Castaic is an unincorporated community of about 19,000 people in the north Santa Clarita Valley, north of the City of Santa Clarita along Interstate 5. It is not a city. Building permits run through Los Angeles County Public Works (Building & Safety). Castaic is anchored by Castaic Lake — a major LA County reservoir + recreation destination — and the Castaic State Power Plant.
Unincorporated LA County, not LADBS
Castaic is unincorporated territory. Building permits go through LA County Public Works (Building & Safety) ↗ under LA County Code Title 22, not the Los Angeles Department of Building and Safety (LADBS). Our address checker pulls real feasibility data for any LA County address; the Castaic-specific permit pathway is detailed below.
Castaic by the numbers
Rounded figures from the 2020 US Census, LA County Assessor parcel data, and LA County DPW permit records.
Population
19,000
2020 Census
Single-family homes
~5,400
LA County Assessor
Median lot size
8,200 sqft
Approximate
ADU permits filed 2025
~48
Source: HCD 2025 total (1,278) distributed proportionally across 2024 per-area shares. 2024: 55.
What makes Castaic different
Castaic is unincorporated despite proximity to Santa Clarita city. Permits run through LA County DPW Building & Safety at the Santa Clarita field office via EPIC-LA. Most parcels east of Interstate 5 face VHFHSZ coverage; some hillside review on foothill parcels.
LA County ADU rules for Castaic
Last verified: 2026-04-15
Current LA County rules from Title 22 of the County Code, as applied to Castaic. State preemption (Gov Code §65852.2) means the county can't reduce below the state baseline. We note where that applies.
| Max detached ADU size | 1,200 sqft (state default) |
| Max ADU height | 16 ft / 18 ft with second-story setbacks |
| Setbacks | 4 ft side / 4 ft rear (state minimum) |
| Permitting agency | LA County Public Works (Building & Safety) |
| Fire-hazard construction | Chapter 7A required on VHFHSZ parcels |
| Local processing time | 60 days from complete submittal (state-mandated) |
Active overlays + extra rules in Castaic
LA County overlays + state-level designations that hit a meaningful share of Castaic parcels.
Very High Fire Hazard Severity Zone (VHFHSZ)
~65% of parcelsMost of Castaic. Chapter 7A construction + defensible space at final.
Castaic Dam inundation area
~15% of parcelsSome southern Castaic parcels sit in the FEMA-mapped Castaic Dam failure inundation area. Disclosure context.
Watch-outs specific to Castaic
- 01
VHFHSZ on majority of parcels
Roughly 2/3 of Castaic sits in the VHFHSZ. Chapter 7A construction (ember-resistant materials, sealed eaves, etc.) is mandatory.
Need a person, not a wizard?
Routes that fit Castaic
Based on what we know about Castaic, these are the lead types that usually make sense here. Pick whichever fits your situation. All free, no obligation.
Complex permit context
Request a Castaic permit referral
Coastal, hillside, historic, fire-zone, or multi-overlay parcels in Castaic usually mean a permit expediter pays for itself in saved months. We work with affiliated Los Angeles permit expediters and expeditors (both spellings) who've handled Castaic projects.
Complex permit context
Request a Castaic permit referral
Coastal, hillside, historic, fire-zone, or multi-overlay parcels in Castaic usually mean a permit expediter pays for itself in saved months. We work with affiliated Los Angeles permit expediters and expeditors (both spellings) who've handled Castaic projects.
Plans that fit Castaic lots
For unincorporated Los Angeles County, the LA County A / B / C pre-approved Accessory Dwelling Unit (ADU) plans are free and usable here. California Department of Housing and Community Development (HCD)-approved prefab also bypasses local plan check entirely.
Amenities + civic services in Castaic
Parks, libraries, and the school district that serve the area. Context that matters for renter appeal, family relocation, and long-term resale.
Parks + sports
Castaic Lake State Recreation Area
Castaic Lake
Major LA County reservoir + recreation area. Boating, fishing, swimming, camping.
Major regional reservoir + recreation
- Fishing
- Trails
- Picnic
Hasley Hills Park
Hillcrest Parkway
Community park.
- Baseball
- Playground
- Picnic
Libraries
Castaic Library
LA County Library
Castaic Road
Public schools
School assignments vary by exact address. Performance levels below are from the official California School Dashboard — California's official accountability system uses colored levels (blue highest, red lowest) rather than 1-10 numeric scores.
District
Castaic Union School District + William S. Hart Union High School District
Getting around Castaic
Car-dependent rural-suburban.
Transit + walkability
Bus lines
- Santa Clarita Transit
Walkability
Mostly car-dependent.
Nearby airports
Distance + type for each major Los Angeles-area airport reachable from Castaic. Useful for travel, commute, and any flight-path noise concerns on specific parcels.
Hollywood Burbank Airport (BUR)
~28 miRegional / domestic
Community + landmarks in Castaic
Annual events, landmarks, and the places that anchor the area's identity. Context for renter appeal and long-term resale.
What makes Castaic Castaic
Reservoir + recreation
Castaic Lake
324K acre-feet capacity. Part of the California State Water Project. Major LA-area boating + fishing destination.
Nearby areas to Castaic
Other Los Angeles-area pages worth a look. Each one runs different Accessory Dwelling Unit (ADU) rules depending on jurisdiction — we show you what changes when you cross a city or county line.
LA County unincorporated
Stevenson Ranch →
Premium master-planned SCV unincorporated community. LA County (not Santa Clarita) jurisdiction + HOA architectural review + Very High Fire Hazard Severity Zone (VHFHSZ) coverage on western parcels shape the Accessory Dwelling Unit (ADU) calculus.
LA County unincorporated
Val Verde →
Small SCV unincorporated community with significant Black-American civil-rights heritage (former Eureka Villa resort). LA County jurisdiction shapes the Accessory Dwelling Unit (ADU) calculus.
LA County unincorporated
Agua Dulce →
Rural SCV unincorporated community with multi-acre lots + iconic Vasquez Rocks adjacency. Equestrian zoning + LA County jurisdiction + VHFHSZ coverage shape the Accessory Dwelling Unit (ADU) calculus.
Other permits in Castaic
LA County Public Works (Building & Safety) handles ADU, solar, and garage-conversion permits for Castaicand the rest of unincorporated LA County. We've broken each out as its own pathway page.
Frequently asked questions about Castaic ADUs
›Can I build an ADU in Castaic?
Yes. Castaic allows ADUs under LA County Code Title 22, aligned with California Gov Code §65852.2. Most single-family lots can host one ADU plus one JADU. Permits go through LA County Public Works (Building & Safety), not LADBS, since Castaic is unincorporated territory rather than a city.
›Why does Castaic use LA County rules instead of LA City rules?
Castaic is unincorporated. It's never been formally incorporated as its own city, so LA County serves as the local government. Building permits, zoning, sheriff, libraries (in many cases), and most other services run through county departments rather than city ones.
›Where do I submit my Castaic ADU permit?
Online via LA County's EPIC-LA portal, or in-person at the LA County Public Works Building & Safety counter in Alhambra (900 S. Fremont Avenue). The EPIC-LA online portal handles most ADU submittals end-to-end, so you rarely need to visit in person.
›How long does the ADU permit process take in Castaic?
LA County DPW targets the state-required 60-day plan check for ADUs from a complete submittal. Hillside, VHFHSZ, or environmental-review parcels can extend timelines by 4 to 12 weeks. Castaic-specific overlays may add additional time. See the watch-outs above.
›Are LA County's pre-approved ADU plans free?
Yes. LA County maintains three pre-approved standard ADU plans (Plans A, B, and C) usable in any unincorporated area, including Castaic. They're free to use, similar to LADBS's YOU-ADU program. The trade-off is reduced design flexibility, but for a fast, low-cost permit path they're the strongest option.
Ready to see what your Castaic lot can do?
Our free address checker pulls real zoning, overlay, and parcel data for any Los Angeles County address, including unincorporated Castaic. Start there and we'll surface what applies to your specific lot.
Check your address →Reviewed by Yair Harpaz, Founder, PermitPathLA. California DRE-licensed broker with 30+ years of Los Angeles real estate and mortgage industry experience.
Castaic ordinance data last reviewed .
See an error or stale rule? corrections@permitpath.la
Primary sources: LA County DPW ADU info · LA County Code Title 22