What happens if you skip the permit (and you needed one)
- Stop-work orders from Simi Valley code enforcement carry a $250–$500 fine per day of unpermitted work, and you'll owe double permit fees to legalize the unit after the fact.
- Your lender or title company will flag unpermitted construction during refinance or sale: Simi Valley requires a Certificate of Occupancy for any habitable space, and lenders won't fund a property with missing permits until the work passes final inspection.
- Liability and insurance claims on unpermitted ADU work are routinely denied—if a renter or visitor is injured, your homeowner policy will not cover it, and you personally face a lawsuit.
- Neighbor complaints trigger Simi Valley Planning or code enforcement investigation; if the ADU is nonconforming (setback, height, or use violation), the city can issue a Cease and Desist notice and levy fines of $100–$300 per day until you remove the unit or obtain retroactive approval.
Simi Valley ADU permits — the key details
California Government Code § 65852.2 (amended by AB 881 in 2021) mandates that Simi Valley must approve ADUs ministerially—meaning the city cannot deny the project on discretionary grounds like 'compatibility' or 'neighborhood character.' However, the city can still require that your ADU meets objective standards: for a detached ADU, lot size must be at least 5,000 square feet (state minimum); setbacks from side and rear property lines are 5 feet minimum (not 15 feet as in some single-family zones); height is capped at 35 feet (or match primary dwelling, whichever is lower); and parking is waived for ADUs in Simi Valley. Simi Valley's code does not impose local parking requirements for owner-occupied or rented ADUs, aligning with state law and removing a major cost driver in other jurisdictions. For a junior ADU (a bedroom added within the primary home), lot size and setbacks do not apply—only building envelope (no more than 500 sq ft, 20 feet tall). If you have a nonconforming lot (e.g., 4,500 sq ft in Simi Valley's General Plan), you cannot build a detached ADU unless the city grants a variance, which is discretionary and time-consuming. Always check your lot size and deed restrictions before hiring an architect.
Simi Valley Building Department does NOT offer pre-approved ADU plan catalogs (unlike San Francisco, Los Angeles County unincorporated areas, and some other California jurisdictions). You must hire an architect or designer to prepare site plan, floor plan, roof plan, foundation and framing details (if detached), electrical schematic, plumbing isometric, and energy-compliance documents (Title 24 Part 6). Plan review takes 45–70 days; if the city issues a Reduction in Scope letter (common for ADUs under 800 sq ft), you may skip structural stamping and use simple prescriptive details for foundation and framing. Simi Valley's permit application portal requires submission of PDF documents, plot plan from county assessor, preliminary title report (to verify no restrictive covenants), and a site-development plan showing setback measurements and utility locations. The permit fee is approximately 1% of estimated construction cost (so a $150,000 ADU yields a $1,500 base permit fee), plus plan-review fees of $1,500–$3,000 depending on complexity, plus mechanical/electrical/plumbing plan-check fees of $300–$500 each. Total processing cost is typically $3,500–$7,000 before you pour concrete or frame.
Detached ADUs in Simi Valley must show a separate foundation plan if the lot is in a seismic zone (Simi Valley is in zone 3, per USGS), and you must prove that the foundation meets IRC R403 requirements for shallow post footings or slab-on-grade. If your lot is in the western portion of Simi Valley (closer to the coast, near Los Olivos Canyon), you may be in a flood plain per Ventura County's FEMA maps; request a FEMA flood certificate from the city before design. Frost depth is minimal in Simi Valley (0–6 inches in the valley floor), so post footings 18 inches deep are typical and sufficient. If you are adding a second-story or mezzanine ADU, the city will require structural calculations stamped by a civil engineer, adding $800–$1,500 to your pre-construction costs. Detached ADUs must also have a separate utility meter or sub-meter for water and electricity; if you are tying into the primary dwelling's meter, Southern California Edison and the city require a written utility allotment agreement and a separate breaker panel for the ADU (adding $500–$1,200 to MEP costs). Simi Valley does not waive sprinkler requirements on ADU lots if total lot square footage plus ADU square footage exceeds 5,000 sq ft in certain fire zones; confirm with the city's Fire Department during pre-application.
The 60-day ministerial approval clock (per AB 671) begins when the city deems your application complete. Simi Valley's completeness threshold is strict: missing a plot plan, preliminary title report, or energy-compliance form will start the clock over. Once deemed complete, the city has 60 days to approve or conditionally approve; if they do not issue a decision by day 60, the permit is automatically deemed approved (though you may still need to receive it in writing). In practice, Simi Valley typically issues permits within 50–65 days for straightforward ADUs. Expect two to three rounds of minor corrections (setback clarification, utility diagram refinement) before approval. Inspections after permit issuance include foundation (if detached), framing, rough MEP, insulation, drywall, and final building inspection, plus a separate utility final (water meter, electrical) and planning final (confirming setbacks and use match the permit). Total construction timeline is 12–20 weeks depending on weather, crew availability, and city inspection scheduling.
Owner-builder permits are allowed in California for ADU construction if you own the property and occupy either the primary dwelling or the ADU as your principal residence. You cannot be a licensed contractor (contractor license revocation for owner-builder permits is automatic). You must contract out all trades requiring state licenses: electrical work requires a California licensed electrician (Electrical Contractor or electrician journeyman/apprentice supervised by a contractor); plumbing requires a licensed plumber; HVAC requires an HVAC contractor. You can perform demolition, framing, drywall, finish painting, and landscaping yourself as the owner-builder. The owner-builder permit fee is slightly lower than a standard permit (typically 10–15% discount), and Simi Valley will accept a one-page affidavit in place of a contractor's insurance certificate. If you hire a general contractor to manage the ADU build, you no longer qualify for owner-builder status, and the GC must carry a California Contractors License (ABC-classified as B, C-7 for most residential work, or B for general building). Simi Valley's permit application will ask whether the applicant is owner-builder; answer truthfully, as misrepresentation can result in permit revocation and civil penalties.
Three Simi Valley accessory dwelling unit (adu) scenarios
State ADU law overrides Simi Valley zoning — AB 881 and ministerial approval
In 2021, California Assembly Bill 881 amended Government Code § 65852.22 to require cities like Simi Valley to approve ADUs ministerially—without discretionary conditional use permits, variances, or design review. Prior to AB 881, Simi Valley's R-1 zoning code classified ADUs as conditional uses, meaning the Planning Commission could deny an ADU based on subjective criteria like 'neighborhood compatibility' or 'viewshed impact.' AB 881 eliminated that discretion. Today, Simi Valley MUST approve your ADU if it meets objective standards: lot size (5,000 sq ft detached minimum), setbacks (5 feet rear/side), height (35 feet or match primary, whichever lower), and parking (waived). Importantly, the city cannot impose local parking requirements, design restrictions (e.g., 'must match primary home's architectural style'), or neighborhood-compatibility conditions. If Simi Valley denies your ADU or adds discretionary conditions, you can appeal to the Planning Commission and cite AB 881; the burden shifts to the city to prove your project violates a stated objective standard.
Ministerial approval also comes with a 60-day shot clock under AB 671. Once the city deems your application complete (all required documents submitted), the city has exactly 60 days to approve or conditionally approve. If the city issues a second-review request or incomplete notice, the clock pauses and restarts when you resubmit. If the city fails to issue a decision by day 60, your permit is deemed approved—you do not need the city's written approval to proceed with permits and construction, though in practice you should request a written deemed-approved letter to avoid confusion with inspectors. Simi Valley Building Department is aware of this requirement and typically issues permits within 50–65 days for standard ADUs.
One caveat: ministerial approval does NOT exempt you from California Environmental Quality Act (CEQA) review. Simi Valley must prepare a Categorical Exemption (typically CEQA Class 31 for in-fill ADU projects) or a Negative Declaration before issuing the permit. This step adds 5–10 days to the timeline and costs $200–$500 (city processing fee) but does not typically result in denial; the exemption is nearly automatic if your ADU is on an existing residential lot with no sensitive habitats or cultural resources. Always ask the city at pre-application whether your lot triggers any CEQA concerns.
Restrictive covenants in your deed (e.g., 'this lot is restricted to single-family residential use') may still override state law if the covenant predates AB 881. If your property is in a Homeowners Association (HOA) or subject to a Conditions, Covenants & Restrictions (CC&Rs) document, request a preliminary title report from an escrow company and confirm whether ADUs are prohibited. Many HOAs have added ADU-friendly CC&R amendments after AB 881, but older HOAs have not. Simi Valley will issue a permit even if HOA rules prohibit ADUs, but the HOA may sue you for a violation of the CC&Rs; you must resolve the HOA restriction before breaking ground or face a court injunction to remove the ADU.
Utility connections and sub-metering — separate meters and costs
California Building Code § 422.2 and Southern California Edison's Rule 16 require ADUs to have separate utility service or sub-metering if the ADU is a habitable, financially independent unit (i.e., you are renting it or it will be rented). For a detached ADU, the simplest approach is a second electrical service panel and water meter directly from the utility grid; this requires trenching for a second lateral (water line) and conduit (electrical service), adding $1,500–$3,000 to MEP costs depending on distance from the main connection. For a garage conversion or junior ADU (additions to the primary home), sub-metering is standard: you install a sub-panel downstream of the primary home's main panel, with a separate breaker dedicated to the ADU, and a water sub-meter on the supply line to the ADU bathroom and kitchen. Sub-metering costs $600–$1,200 total and is far cheaper than a second service.
Southern California Edison requires a separate meter for each habitable unit to enable rental rates or cost-allocation. If you are owner-occupying the ADU (living in the ADU yourself while renting the primary home, or vice versa), you may be able to use sub-metering and avoid a second service, but SCE and the city will ask you to sign an owner-occupancy affidavit or deed restriction. Simi Valley standard practice is to record a CCR restriction on junior ADUs and some detached ADUs stating 'ADU is owner-occupied by the property owner; ADU shall not be rented to a third party without written consent of the city.' If you later want to rent the ADU, you must amend or release the restriction. For detached ADUs, Simi Valley does not typically impose an owner-occupancy restriction, allowing you to rent from day one—so a separate meter is the cleaner path.
Water meter installation requires coordination with the city's Water Department and SCE's service connection team. Allow 30–45 days from permit issuance to utility-ready conditions (meter installed, service lines trenched, final electrical rough-in). If the primary home's water meter is already near-full capacity (city utilities will run a load test), you may need to upgrade the main service line, which triggers a city water-impact fee ($200–$500) and longer timeline. Ask the city at pre-application whether a water-demand increase requires utility upgrades. Plumbing and electrical trades must coordinate meter installation with the utility company; most licensed contractors handle this as part of their scope, but confirm the cost estimate includes meter setup.
Simi Valley's utility connection process is relatively streamlined compared to larger California cities, as Southern California Edison and Ventura County Water Agency have pre-set procedures for ADU sub-metering. Most ADU projects secure utility approval within 15 days of permit issuance. However, if your property is in a hillside or fire-zone area (eastern Simi Valley near Santa Susana Pass), the utility may require underground-only service (no overhead lines), adding cost and time. Confirm utility jurisdiction and service type during pre-application with the city planner.
Simi Valley City Hall, 2929 Tapo Canyon Road, Simi Valley, CA 93063 (Building Permits Division, 1st floor)
Phone: (805) 583-6700 ext. 6400 (Building Department main line; ask for Building Permits) | https://www.simi.org (search 'permits' for online portal and applications; also accepts paper submittals in person)
Monday–Friday, 8:00 AM – 5:00 PM (closed weekends, city holidays)
Common questions
Can I build an ADU in Simi Valley if my lot is smaller than 5,000 square feet?
Only if you are building a junior ADU (a bedroom and bathroom added to the primary home with no separate kitchen). Junior ADUs have no lot-size minimum under California Government Code § 65852.22. For detached ADUs or garage conversions, your lot must be at least 5,000 square feet. If your lot is smaller (e.g., 4,500 sq ft) and you want a detached ADU, you can request a variance from Simi Valley Planning Commission, but this is discretionary and typically denied unless the lot is nearly 5,000 sq ft. Most applicants in this situation choose to convert an existing garage or add a junior ADU instead.
Does Simi Valley require me to rent the ADU, or can I live in it myself?
You can do either. Simi Valley does not impose an owner-occupancy requirement on most detached ADUs (state law allows you to rent it), but some projects may be subject to a recorded CCR restriction if the Planning Department flags a neighborhood concern during ministerial review. Junior ADUs and garage conversions often come with an owner-occupancy condition in Simi Valley's permit, meaning you must occupy either the primary home or the ADU as your principal residence; if you later want to rent both units, you must request a CCR amendment from the city. Ask the city at pre-application whether your lot will trigger an occupancy restriction.
What is the difference between an ADU and a junior ADU in Simi Valley?
An ADU is a separate habitable unit with its own kitchen, bathroom, and separate or independent entrance. A junior ADU is a bedroom and bathroom added to the primary home that shares the primary kitchen and may have interior circulation (not a completely separate unit). Junior ADUs are smaller (max 500 sq ft), have no lot-size requirement, and do not count toward single-family zoning limits. ADUs are larger (typically 400–1,200 sq ft) and have their own kitchen and entrance. In Simi Valley, both require permits and are approved ministerially under state law, but junior ADUs have faster plan review because no foundation or separate utility requirements apply.
How much does a permit cost for an ADU in Simi Valley?
Permit costs typically range from $3,500 to $7,000 total, broken down as: base permit fee (1% of estimated construction cost, so a $150,000 ADU is $1,500), plan-review fees ($1,500–$3,000), and MEP (mechanical/electrical/plumbing) plan-check fees ($300–$500 each). If you need a structural engineer for a detached ADU or floodplain review, add $800–$1,500. Simi Valley does not charge impact fees or development fees for ADUs, unlike some California cities. Always confirm current fees with the Building Department, as they are updated annually.
Can I pull an owner-builder permit for my ADU in Simi Valley?
Yes. California Building & Profession Code § 7044 allows owner-builders to pull permits for projects on their own property. You must own the property, occupy either the primary home or the ADU as your principal residence, and not be a licensed contractor. You can perform demolition, framing, drywall, and finish work yourself; electrical, plumbing, HVAC, and gas work must be contracted to licensed professionals. Simi Valley will waive the contractor's insurance requirement and accept an owner-builder affidavit. Owner-builder permits are typically 10–15% cheaper than standard contractor permits. If you hire a general contractor to manage the project, you lose owner-builder status and the GC's license is required.
How long does it take to get an ADU permit in Simi Valley?
Plan review typically takes 45–70 days from the date the city deems your application complete. Simi Valley's 60-day ministerial approval clock (per AB 671) begins on that date, so you should receive a permit decision within 60 days. Two to three rounds of minor corrections are typical before final approval. If you need a structural engineer review (detached ADU) or floodplain certification (west Simi Valley), plan review may extend to 70 days. Once the permit is issued, construction inspections (foundation, framing, MEP, final) take 8–16 weeks depending on size and crew speed.
What if my property is in a Homeowners Association — can I still build an ADU?
Simi Valley will issue a permit regardless of HOA rules, but the HOA may have CC&Rs (Conditions, Covenants & Restrictions) that prohibit ADUs or require HOA approval. State law does not override private HOA restrictions, so you must check your CC&Rs or HOA bylaws and request written approval (or amend the CC&Rs) before breaking ground. If the HOA denies ADU approval and you build anyway, the HOA can sue you for a covenant violation and potentially force removal of the ADU. Always resolve the HOA restriction first—it is cheaper and faster than litigation after construction.
Do I need a parking space for an ADU in Simi Valley?
No. California Government Code § 65852.2 waives off-street parking requirements for ADUs in all jurisdictions, including Simi Valley. This saves significant cost (a parking space typically costs $3,000–$5,000 to construct) and is one of the biggest advantages of building an ADU. Simi Valley cannot impose a parking requirement or condition for ADUs. However, on-street parking must be available in your neighborhood, and guests and residents must not block fire lanes or create a public-safety hazard.
What inspections are required for an ADU in Simi Valley?
Detached and garage-conversion ADUs undergo full building inspections: foundation (if detached), framing, rough mechanical/electrical/plumbing, insulation, drywall, and final building. Junior ADUs may skip foundation inspection if added to primary home. All ADUs require a utility final (water meter, electrical service verification) and a planning final (confirming setbacks and use match the permit). Simi Valley schedules inspections 3–5 business days after a phone request; inspectors typically pass projects on the first attempt if work matches plans. Budget 8–16 weeks for inspections depending on project size and crew scheduling.
What is the difference between a detached ADU and a garage conversion in Simi Valley?
A detached ADU is a new building on the lot with its own foundation, roof, and utilities. A garage conversion reuses an existing structure (typically a 2-car garage) by converting the interior into a habitable unit with kitchen and bathroom. Detached ADUs require more planning (foundation, grading, utility extensions) and cost more ($100,000–$250,000 typically); garage conversions are faster and cheaper ($80,000–$150,000 typically) because the structure already exists. Simi Valley approves both ministerially under state law. Garage conversions require a licensed plumber to relocate utilities and add egress windows; detached ADUs require utility trenching and a possible structural engineer for seismic design. Both have the same 60-day permit timeline.