Castaic ADU permits go through LA County, and what else you need depends on your tract. Live Oak has no HOA, while Hasley Hills and Williams Ranch generally require HOA review, and some outlying parcels face fire zone rules.
Exploring Castaic, CA: A Perfect Place for ADUs and Outdoor Adventures
Castaic Lake, I-5 Access, and Neighborhoods That Range From No-HOA to Mello-Roos
Castaic sits along the I-5 corridor just north of Six Flags Magic Mountain, with Castaic Lake State Recreation Area — an upper and lower lake with boating, camping, and hiking — a few miles north of most neighborhoods. Housing here spans a real range: Live Oak, west of the freeway, has no HOA and tends to offer some of the more affordable housing in the Santa Clarita Valley. Hasley Hills, tucked into Hasley Canyon, has five separate neighborhoods, most with an HOA but low or no Mello-Roos. Williams Ranch, the newest development, is a partially gated, 430-acre community still under construction with roughly 497 homes planned — and it does carry an annual Mello-Roos assessment.
What to Check Before You Build in Castaic
Castaic is unincorporated LA County, so ADU permits go through the County’s Department of Regional Planning (Title 22, §22.140.640), not a city office. Because HOA rules and Mello-Roos assessments vary block by block here — Live Oak has neither, Williams Ranch has both — confirm your specific tract’s HOA design-review requirements and any bond assessments before finalizing your ADU plans. Some outlying Castaic parcels also border wildland areas subject to fire hazard severity zone access rules, which apply on a lot-by-lot basis.
Benefits of Adding an ADU in Castaic
- Flexible Living Arrangements: Room for family or guests across a range of lot sizes, from Live Oak to Williams Ranch.
- Rental Opportunities: Easy I-5 access supports steady rental interest from commuters.
- Property Value Growth: A well-planned ADU adds value in a community with a growing mix of housing options.
Castaic ADU quick facts
| Permits | LA County (Regional Planning, then Public Works Building & Safety) |
| HOA review | Varies by tract: none in Live Oak, common in Hasley Hills and Williams Ranch |
| Mello-Roos | Varies by tract; Williams Ranch carries an annual assessment |
| Fire hazard zones | Some outlying parcels near wildland areas |
| Rentals | Over 30 days for every JADU and most garage conversions; check county rules for others |
Which ADU types fit Castaic lots?
- Live Oak: no HOA review, so a detached ADU or garage conversion only needs county approval.
- Hasley Hills and Williams Ranch: an attached ADU or Junior ADU is often easier to fit through HOA architectural review.
- Outlying parcels: check fire-zone access rules before choosing where a detached unit goes.
How does ADU permitting work in Castaic?
- Check your parcel. LA County’s free Z-NET map shows your parcel’s zoning. The county’s Department of Regional Planning page summarizes the ADU rules.
- Regional Planning review. The Department of Regional Planning approves the site plan for zoning, setbacks, and height.
- Building & Safety plan check. LA County Public Works Building & Safety then reviews the construction plans, typically submitted online through EPIC-LA.
- Decision and fees. A compliant ADU gets ministerial approval with no public hearing, and a decision is due within 60 days of a complete application. New living space over 500 square feet generally triggers school district fees.
The county also offers Pre-Approved ADU Standard Plans. They cut plan review time, but they can’t be modified, and you still need a site-specific plot plan approved by Regional Planning.
Castaic ADU FAQs
Where do I apply for an ADU permit in Castaic?
Castaic is unincorporated LA County, so you apply to the LA County Department of Regional Planning, not the City of Santa Clarita. After Regional Planning approves the site plan, LA County Public Works Building & Safety reviews the construction plans.
Can I use a pre-approved ADU plan in Castaic?
Yes. LA County offers pre-approved ADU standard plans that speed up plan review. They can’t be changed, and you still need a site-specific plot plan approved by Regional Planning.
Does my Castaic HOA get a say in my ADU?
If your tract has an HOA, usually yes. HOAs can’t ban ADUs, but most require architectural review of exterior design. Live Oak has no HOA, while Hasley Hills and Williams Ranch tracts generally do.
Ready to explore your options in Castaic? Contact Santa Clarita ADU or call (661) 486-8393 to get connected with a local ADU contractor.
Looking for a builder? See how we connect Castaic homeowners with a local ADU contractor.