Simi Valley ADU: Regulations, Costs & Permits

Simi Valley's Department of Environmental Services handles ADUs. Planning issues a ministerial Zoning Clearance, then Building & Safety issues the building permit. Building & Safety accepts submittals online. On a lot with an existing home, the city must approve or deny a complete application within 60 days.

• State Exempt: ADUs that fit state minimums, such as a detached unit up to 800 sq ft, one story, 18 ft tall, with 4 ft side and rear setbacks. No extra local standards and no parking.
• Non-State Exempt: generally new attached ADUs and detached ADUs over 800 sq ft. These get a 20 ft front setback, design matching, window limits, 6 ft separation from other buildings, and usually one parking space.
• Why it matters: keeping a detached ADU at 800 sq ft or less is the simplest path in Simi Valley. Going bigger buys space but brings the local rules with it.

• Detached: up to 1,000 sq ft on lots of 8,000 sq ft or less, and 1,200 sq ft on larger lots. A detached ADU can also have an attached garage up to 400 sq ft and a patio cover up to 10% of its living area.
• Attached: 850 sq ft or 50% of the main house, whichever is larger, up to 1,000 sq ft. It must share at least 10 ft of wall with the house.
• JADU: up to 500 sq ft within the house. JADUs are no longer allowed in the RH and RVH zones.
• Height: detached ADUs are one story and 18 ft, or up to 20 ft near major transit to match the main roof pitch. Attached ADUs can go two stories or over a garage at 25 ft, or 30 ft with 10 ft side and 20 ft front and rear setbacks.

• Materials: attached ADUs match the house's exterior materials and colors. Detached ADUs use at least one material and one color from the house.
• Windows: no windows above the first 10 ft of a wall, and no second-story windows facing neighbors unless you meet 10 ft side and 20 ft rear setbacks.
• Rear yard: accessory structures, including the ADU, can cover no more than 40% of the first 10 ft of a side yard and the required 20 ft rear yard, and at least half the rear yard width near the back line must stay open.
• Parking: one space, except for studios, lots within half a mile of transit, garage conversions, historic districts, and ADUs built with a new home.

• Hillside lots: on lots under the city's Hillside Performance Standards, only State Exempt ADUs are allowed, which in practice caps most new detached units at 800 sq ft. Driveways and site work must meet the hillside rules.
• Fire: Ventura County Fire adopted the state's 2025 fire hazard severity zone maps effective July 1, 2025. Check your parcel on the VCFD map viewer before you design.

• Impact fees: none under 750 sq ft. Larger ADUs pay proportionally to the size of the main house.
• Water: two providers, Ventura County Waterworks District No. 8 (city-managed) or Golden State Water. Your provider also decides how sewer is billed.
• JADU rules: a deed restriction is recorded before Zoning Clearance, the JADU can't be sold separately, and the owner must live on site if the JADU shares a bathroom with the house.
• Rentals: 30 days or longer.

How big can an ADU be in Simi Valley?

A detached ADU can be up to 1,000 sq ft on lots of 8,000 sq ft or less and 1,200 sq ft on larger lots. Units at 800 sq ft or less that meet state minimums skip most local standards.

Can I build an ADU on a hillside lot in Simi Valley?

Yes, but only the state-exempt type, which in practice means most new detached units top out at 800 sq ft and one story.

Does a Simi Valley ADU need parking?

Not if it's a state-exempt unit. Larger ADUs usually need one space, with exemptions for studios, garage conversions, and lots near transit.

Are the ADU rules I found online for Simi Valley current?

Maybe not. Ordinance 1373, adopted in July 2026, replaced the 2023 rules, and many older guides still show the old limits.

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