Castaic ADU Builder in Unincorporated LA County

Castaic ADU Permits Through Los Angeles County

Castaic has never been part of the City of Santa Clarita, so the county handles ADUs. The application starts with the Department of Regional Planning, filed on the county's EPIC-LA portal. After the zoning approval, Public Works Building & Safety reviews the construction drawings, issues the permit and inspects the work.

State law applies here exactly as it does in the city: ADU review must be ministerial, county staff get 15 business days for a completeness ruling, and it must act on a complete application within 60 days. Correction rounds still add time, and county plan check may ask for different supporting documents than the city does, so we prepare the file for the county's checklist from the start.

Tract Homes and Rural Lots Across Castaic

Castaic is two communities in one. Newer subdivisions on the hills east and west of the freeway look much like Santa Clarita tracts, with two-story homes, attached garages and HOAs. ADUs there tend to be garage conversions, junior ADUs and modest backyard units, often with HOA design review.

Older parts of Castaic and canyons on its edges hold larger lots, some zoned for horses or light agriculture. Those parcels have room for a detached guest house but bring the issues of rural land: long driveways, slopes, private roads and utility service that may not match what a suburban lot has. On those properties the site investigation is a bigger part of the job.

• Newer tracts: garage conversions and JADUs
• Rural lots: detached guest houses
• Check septic or sewer before design
• Confirm the water provider for the parcel

Septic, Sewer and Water for a Castaic ADU

Not every Castaic parcel is connected to a public sewer. On a property with a septic system, an ADU adds wastewater load, and the county's Environmental Health division will need to see that the system can handle it or will be expanded. Septic capacity can decide the size of the ADU or whether a new system is needed.

Water service varies by location. Some parts of the community are served through SCV Water and others by different local providers, and a few rural properties may rely on wells. We confirm the provider and the meter situation early, along with fire flow and hydrant distance, which LA County Fire reviews. Power comes from Southern California Edison.

Fire Hazard and Hillside Rules in Castaic

Castaic is surrounded by brush-covered hills and the open land around the lake. A good share of parcels fall inside mapped hazard zones, and the 2025 state remapping pushed the Very High boundary outward in several places. An ADU in one of those zones is built to Chapter 7A, and defensible space must be maintained.

Hillside lots bring grading, soils and drainage requirements from county Public Works. A detached unit on a slope may need an engineered foundation and retaining walls. Native oaks on rural parcels may be protected under the county's oak tree rules, which we check before siting the unit.