Quick Answer: ADUs in Simi Valley cost $60,000–$280,000 in 2026 depending on type. Garage conversions run $60K–$120K. Attached ADUs cost $110K–$200K. Detached ADUs (new construction) run $140K–$280K. Above-garage ADUs cost $200K–$350K. JADUs (junior ADUs within the home) cost $35K–$75K. A 1-bedroom detached unit generates $1,800–$2,400/month in Simi Valley's rental market. Safeway Construction has built ADUs across Ventura County for 20+ years — CA Lic #1066117.
How Much Does an ADU Cost in Simi Valley?
Building an ADU in Simi Valley costs $60,000 to $280,000 in 2026 — depending on the type, size, and what your property already has to work with. A garage conversion on a flat lot in East Simi Valley costs a very different number than a detached 800-square-foot cottage in Wood Ranch. That range is wide, but the variables that drive it are straightforward.
Simi Valley is one of the stronger ADU markets in Ventura County. Median home values around $780,000, solid rental demand, and a city permitting process that has improved significantly since California's 2020–2022 ADU reform laws. If you've been sitting on the idea of an ADU, 2026 is a realistic year to act. Check out our 2026 California ADU law guide to see how new rules affect your Simi Valley project.
Want a quick ballpark before reading further? Try our free AI estimator at our free cost calculator — answer 5 questions, get a real price range in about 2 minutes. No contractor visit required.
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ADU Cost by Type in Simi Valley (2026)
| ADU Type | Typical Cost Range | Best For |
|---|---|---|
| Detached ADU (new construction) | $140,000 – $280,000 | Maximum rental income, most privacy |
| Attached ADU (addition to home) | $110,000 – $200,000 | Smaller lots, shared utility connections |
| Above-Garage ADU | $200,000 – $350,000 | Maximize privacy on smaller lots |
| Garage conversion ADU | $60,000 – $120,000 | Fastest path, lowest entry cost |
| Junior ADU (JADU) | $35,000 – $75,000 | Within main house, under 500 sq ft |
Detached ADU: New Backyard Construction
$140,000 – $280,000
A standalone structure in the backyard is the most popular ADU type among Simi Valley homeowners. It commands the highest rental rates, gives tenants full privacy, and adds the most resale value.
| Size | Cost Range | Finishes |
|---|---|---|
| 400 sq ft (1BR/1BA) | $120,000–$165,000 | Basic slab, flat lot |
| 600 sq ft (1BR/1BA) | $150,000–$220,000 | Standard finishes |
| 800 sq ft (2BR/1BA) | $180,000–$280,000 | Premium, sloped lots +$15K–$35K |
| 1,000+ sq ft | $220,000–$350,000 | Premium finishes, complex sites |
The low end ($140,000–$165,000) covers a 400–500 sq ft unit on a slab foundation: 1 bedroom, 1 bathroom, full kitchen, basic finishes, and all utility connections. The high end ($220,000–$280,000) reflects a 700–850 sq ft unit with premium finishes, or a project on a sloped lot in Wood Ranch or Big Sky where grading and a stepped foundation add $15,000–$35,000.
Per square foot: $280–$380/sq ft standard. Premium finishes or sloped sites push toward $400–$450/sq ft.
Garage Conversion ADU
$60,000 – $120,000
Lowest-cost ADU path & fastest ROI in Simi Valley
Most Simi Valley single-family homes have attached 2-car garages in the 400–500 sq ft range. Converting that existing shell is the fastest and most cost-effective ADU path available. The foundation is there. The structure is there. You're converting, not building from scratch.
Garage Conversion Cost Breakdown:
- • Standard 1-car garage (170–200 sf): $60,000–$80,000
- • Standard 2-car garage (350–400 sf): $80,000–$120,000
- • Oversized 2-car (450+ sf): $90,000–$130,000
- • Parking replacement cost: +$8,000–$20,000
- • Fire separation walls: +$4,000–$8,000
- • Egress windows (2): +$2,000–$4,000
The $60,000–$80,000 budget covers framing, insulation, drywall, a mini-split HVAC system, new electrical, plumbing for kitchen and bathroom, egress windows, and basic finishes. Above $80,000, costs increase for second bathrooms, premium kitchens, exterior appearance upgrades, or replacing a settled original slab.
One planning note: Simi Valley requires a compliant parking replacement plan when you convert a garage. We handle this analysis during the permit phase.
Attached ADU
$110,000 – $200,000
An attached ADU shares one or more walls with the main house. Think of it as a room addition with a full kitchen, bathroom, and private entrance. It costs more per square foot than a garage conversion but less than a fully detached structure because it shares the existing foundation and often part of the roofline. Savings vs. detached: $12,000–$18,000 on foundation/framing, $8,000–$12,000 on utilities.
Attached ADUs work well on lots where the backyard is too small for a detached structure, or on corner lots where a side-yard addition is possible. Simi Valley setback requirements: Minimum 4 feet from property line.
Typical cost for a 500 sq ft attached ADU: $18,000–$38,000 for foundation and framing, $18,000–$32,000 for plumbing and electrical, $5,000–$10,000 for HVAC, $18,000–$35,000 for finishes, and $8,000–$18,000 for permits and school fees.
Above-Garage ADU
$200,000 – $350,000
An above-garage ADU is built on top of an existing garage, combining the privacy of a detached unit with minimal land footprint. This option works well on narrow or irregularly shaped lots where a detached structure isn't feasible. It represents a middle ground: more private than an attached addition, more efficient land use than a full detached ADU.
Cost Components: Structural reinforcement of existing garage ($15K–$35K), new roofline and ceiling height changes ($12K–$25K), interior staircase access ($8K–$15K), full interior buildout ($80K–$150K), and permits/fees ($5K–$10K). The existing garage must be structurally sound; if it requires foundation repair, add $10K–$20K.
Simi Valley considerations: Many properties have post-and-beam garages requiring structural engineering review before building above them. Setback compliance (4-foot minimum on split lots) and parking requirements still apply. Above-garage ADUs typically command rental rates similar to detached units ($2,000–$2,400/mo for a 1BR).
Junior ADU (JADU)
$35,000 – $75,000
A JADU is a unit of 500 square feet or less created within the existing walls of the main home. Common candidates: an oversized master bedroom with an en-suite, a large bonus room, or a finished lower level on a hillside home. The owner must occupy either the main home or the JADU. JADUs are the lowest-cost ADU option — much of the structure already exists. You're adding a separate entrance, a basic kitchen area, and reconfiguring interior space.
JADU Cost Range:
- • Converting existing room to JADU: $35,000–$50,000
- • New JADU layout (renovated/reconfigured): $50,000–$75,000
- • Owner-occupancy requirement: Must live in main home OR JADU
- • No additional parking required
- • Typical rental: $1,400–$1,900/month
JADUs are underused because of the owner-occupancy requirement, but they're ideal for multi-generational families or empty-nesters who want to downsize into a JADU while keeping the main home for guest rooms or future use. Many East Simi Valley homes have sprawling single-story layouts perfect for JADU conversion.
What Drives ADU Cost in Simi Valley
Site Conditions
Flat lots in East Simi Valley and central Simi Valley are the most straightforward to build on. Wood Ranch and Big Sky are hillside communities — lots slope, sometimes significantly. Grading, retaining walls, and stepped foundations add $15,000–$45,000 to detached ADU projects in those neighborhoods.
Utility Connections
Running new utility lines from the main home to a backyard ADU is a cost many homeowners underestimate. A 100-foot trench for gas, water, and electrical can add $8,000–$18,000 to your total. The longer the run, the higher the cost.
Finish Level
Basic finishes vs. mid-grade finishes add $15,000–$30,000 to the same footprint. We calibrate finishes to the rental market — there's a point where premium finishes stop increasing your rent but keep increasing your cost.
City Permit Fees and School Fees
The City of Simi Valley charges plan check and permit fees based on project valuation. For most ADUs, total city fees run $4,000–$10,000. Simi Valley Unified School District charges a school developer fee of $4.14 per square foot for new residential construction over 750 sq ft. On an 800 sq ft ADU, that's $3,312. Units 750 sq ft or smaller are exempt under SB 543 (2026).
ADU Financing Options in 2026
Most homeowners finance ADUs through one of these four pathways. Each has different rates, timelines, and down-payment requirements.
HELOC (Home Equity Line of Credit)
Most popular option. Flexible, low closing costs, draw as you build. 2026 terms: 80–90% LTV of home value, variable interest rates (typically 1–2 points above prime), 10-year draw period, 10–20 year repayment.
Example for Simi Valley:
- • Home value: $780,000
- • At 80% LTV: Can borrow $624,000 total
- • Existing mortgage: $400,000
- • Available for ADU: $224,000 ✓
Pros: Only pay interest on what you draw; close to prime rates. Cons: Variable rate risk; requires strong credit (740+); no guarantee of approval.
FHA 203(k) Renovation Loan
Finances the property as-is plus the ADU renovation in one loan. Up to 97% LTV on the post-ADU appraised value. Down payment: as little as 3.5%.
Example for Simi Valley:
- • Current home value: $780,000
- • ADU adds appraised value: +$180,000
- • Post-ADU value: $960,000
- • Max loan at 97% LTV: $931,200
- • Current mortgage: $400,000
- • Available for ADU: $531,200 ✓
Best for: Lower down payments (3.5%), weaker credit than HELOC requires. Timeline: 3–6 weeks approval. Requires licensed contractor (Safeway qualifies) and FHA-approved plans.
Construction Loan
Draw funds as construction milestones are reached. Interest-only during construction, converts to permanent mortgage at completion. Timeline: 8–12 weeks approval.
Best for: Homeowners who want staged funding aligned with build progress. Drawback: Higher fees than HELOC; requires appraisal and loan conversion.
Cash-Out Refinance
Refinance your primary mortgage to pull out equity as one lump sum. All funds funded upfront. Fixed or variable rate options.
Best when: Your current mortgage rate is favorable (refinancing doesn't hurt your rate). Note: CalHFA ADU grant program is currently paused (fully allocated December 2023), but check with City of Simi Valley Planning for any local grant programs.
Simi Valley Permitting Deep-Dive
Permit Fees Breakdown (2026)
| Fee Type | Typical Cost | Notes |
|---|---|---|
| Planning Review | $1,000–$2,000 | Zoning & setback verification |
| Building Permit | $250–$1,200 | Based on project valuation ($0.50–$1.50/sq ft) |
| Plan Check | $500–$1,500 | City review of architectural plans |
| Inspections | $300–$800 | Foundation, framing, MEP, final |
| School Impact Fees* | $0 (≤750 sf) or $3,312–$4,968 (>750 sf) | $4.14/sq ft for units over 750 sq ft |
| Total City + School | $2,500–$6,500 | SB 543 saves $2,000–$4,500 if ≤750 sf |
* SB 543 (effective Jan 2026): ADUs 750 sq ft or smaller are exempt from school impact fees. This is a major savings opportunity — many homeowners choose 750 sf vs. 850 sf to capture this exemption.
Soft Costs (Plans, Engineering, Title 24)
Before you submit to the city, you'll need professional plans and engineering:
- • Architectural plans: $3,000–$8,000 (2–3 weeks)
- • Structural calculations (engineer-stamped): $1,500–$3,500 (1–2 weeks)
- • Title 24 energy compliance report: $1,000–$2,000 (1 week)
- • Soil report (if required by site conditions): $800–$2,000
- • Grading/drainage plan (if sloped lot): $1,000–$2,500
- Total soft costs: $8,000–$20,000
Permitting Timeline
The City of Simi Valley allows 60 days maximum for first review (state mandate). Plan check corrections typically require 2–4 resubmissions, each taking 2–3 weeks.
- 1
Pre-Permit (Design & Engineering): 4–8 weeks
Architectural plans, structural, Title 24, soil report if needed.
- 2
Permit Application & Review: 6–10 weeks
60-day window (state mandate) + resubmissions if needed. Fire/Health reviews run concurrently.
- 3
Permit Issuance & Construction: 14–22 weeks
Foundation, framing, rough MEP, final inspections before Certificate of Occupancy.
Total project timeline: 7–9 months from design start to move-in.
Required Documents for Simi Valley Permits
- ✓ Completed application forms (from City website)
- ✓ Site plan showing lot lines, setbacks, parking
- ✓ Architectural floor plans + elevations
- ✓ Structural calculations (engineer-stamped)
- ✓ Title 24 energy compliance report
- ✓ Fire-rated wall details (if attached or garage conversion)
- ✓ Utility connection plans
- ✓ Grading/drainage plan (if on sloped lot)
- ✓ Proof of property ownership
- ✓ SVUSD school impact fee calculation (if applicable)
ADU Rental Income in Simi Valley 2026
Simi Valley sits between Los Angeles County and the rest of Ventura County — which keeps rental demand steady. Here are current rental rate ranges for ADUs in the local market:
| ADU Size | Monthly Rent | Annual Income | Notes |
|---|---|---|---|
| Studio (under 400 sq ft) | $1,400–$1,800 | $16,800–$21,600 | Lower demand than 1BR |
| 1BR (450–600 sq ft) | $1,800–$2,200 | $21,600–$26,400 | Most demand, most supply |
| 1BR Detached/Premium | $2,000–$2,400 | $24,000–$28,800 | Newest or best finishes |
| 2BR (650–850 sq ft) | $2,200–$2,800 | $26,400–$33,600 | Less supply, higher demand |
Long-Term Rental vs. Short-Term (Airbnb)
Income comparison for a typical 1-bedroom ADU in Simi Valley:
| Metric | Long-Term Rental | Short-Term (Airbnb) |
|---|---|---|
| Monthly Revenue | $2,100 | $2,800 |
| Annual Gross | $25,200 | $33,600 |
| Operating Expenses | 25–30% of gross | 45–55% of gross |
| Net Annual Income | $17,000–$18,000 | $15,000–$18,000 |
| Occupancy Volatility | Low (95%+ typical) | High (60–65%) |
| Management Effort | Low | High (cleaning, turnover) |
Simi Valley regulations are lenient for short-term rentals in 2026, but regulations could tighten. Long-term rental remains the safer long-term strategy.
ROI Example
A $180,000 detached ADU generating $2,000/month produces $24,000/year — a gross yield of 13.3% on the build cost. A permitted ADU also typically adds $150,000–$220,000 in appraised property value. That's a build cost that pays for itself through rental income while the property appreciates simultaneously.
ADU vs. Room Addition: Which Makes More Financial Sense?
| Factor | ADU | Room Addition |
|---|---|---|
| Generates rental income | Yes — $1,800–$2,800/mo | No (unless in-law suite) |
| Adds sq footage to main home | No (separate structure) | Yes |
| Permitting complexity | Moderate (state laws simplified) | Standard building permit |
| Best scenario | Long-term hold, rental income | Family use, resale-focused |
| Cost range | $60K – $280K | $60K – $200K+ |
| Timeline | 10 – 22 weeks | 12 – 22 weeks |
What Would Your ADU Cost?
Get a real price range for your Simi Valley property in about 2 minutes. Our free AI estimator accounts for ADU type, size, and local permit costs — no contractor visit required.
Get Free Estimate at our free cost calculator5 Ways to Reduce Your ADU Cost in Simi Valley
- 1
Start with a garage conversion.
The lowest-cost path. Many Simi Valley homeowners use garage conversion rental income to fund a detached ADU later.
- 2
Keep it under 750 sq ft.
California law exempts ADUs under 750 sq ft from school impact fees under SB 543. This saves $2,000–$4,500. Confirm with us before finalizing your footprint.
- 3
Use standard dimensions.
Odd dimensions increase framing labor and material waste. Even-number dimensions (12x24, 16x24) keep costs down.
- 4
Match finishes to the rental market, not your personal taste.
Mid-grade finishes rent at the same rate as premium finishes in most Simi Valley markets. There's no income upside to upgrading to marble countertops in a $2,000/month rental.
- 5
Permit correctly the first time.
Unpermitted ADUs can't be legally rented, add no appraised value, and create problems at resale. The permit fee is not where to save money.
Property Value Increase & Payback Period
How Much Value Does an ADU Add?
| ADU Type | Build Cost | Appraised Value Added | ROI % |
|---|---|---|---|
| Garage Conversion | $90,000 | $120,000–$140,000 | 133–155% |
| Attached ADU | $155,000 | $145,000–$180,000 | 94–116% |
| Detached ADU (600 sf) | $200,000 | $180,000–$220,000 | 90–110% |
| Detached ADU (800 sf) | $250,000 | $210,000–$260,000 | 84–104% |
Note: These percentages show immediate resale value capture. Long-term appreciation (4–5% annually) further accelerates ROI.
Detailed Payback Period Example
Scenario: $200K Detached ADU (600 sq ft) in Simi Valley
Year 1 Income & Expenses:
- • Rental income: $24,000 (at $2,000/mo)
- • Property tax increase: ~$2,200 (1% of $220K appraised value)
- • Insurance increase: ~$400
- • Maintenance/reserves: ~$3,000
- Net Year 1: $18,400
Payback Calculation:
- • Investment: $200,000
- • Annual net rental income: $18,400
- • Payback (rental income alone): 10.9 years
BUT with Property Appreciation:
- • Simi Valley appreciation: 4–5% annually
- • ADU appreciation: ~$10,000–$13,000/year
- • Total wealth building: ~$23,000/year (rental + appreciation)
- • Accelerated payback: 5–6 years with appreciation factored in
If financed with a HELOC, add equity buildup (~$10,000/year in principal paydown), making total annual wealth building ~$33,000.
SB 9 Lot Splitting & ADUs
Senate Bill 9 (effective 2022, expanded 2026) allows homeowners to split residential lots and build multiple units on what was previously a single-family lot. This opens new possibilities for ADU development.
How SB 9 Works
Lot Split Requirements:
- • Both resulting lots must be ≥ 1,200 sq ft minimum
- • Split must be roughly 50/50 (up to 40/60 allowed)
- • Owner must own property for ≥ 2 years (reduced from 3 in 2024)
- • No owner-occupancy requirement for split lots
Units Allowed After SB 9 Split:
- • Each lot: 1 primary unit + 1 ADU + 1 JADU (max 3 units per lot)
- • Total potential: 2 lots × 3 units = 6 units (but typically 4 units total)
- • School fee exemption (SB 543) applies to ADUs ≤ 750 sq ft
2026 Updates Favorable to ADUs
- • Owner-occupancy requirement reduced from 3 to 2 years post-split
- • Lot splits now explicitly allowed on properties with existing ADUs (if compliant)
- • Cities cannot impose setbacks greater than 4 feet on new units on split lots
- • SB 543 school impact fee exemption applies to ADUs ≤ 750 sq ft
Real Simi Valley Example
Corner Lot (0.5 acre / 21,780 sq ft):
- • Original: Single-family home + detached ADU (2 units)
- • After SB 9 Split: Two 10,890 sq ft lots
- • Lot A: Primary home + detached ADU (2 units)
- • Lot B: Primary home + ADU + JADU (3 units)
- • Total units created from one property: 5 units
- • Annual rental income potential: $120,000–$150,000
SB 9 lot splitting is most valuable for owners with large single lots (≥ 3,000+ sq ft) who plan to stay in the property ≥ 2 years. It's a more advanced strategy than single-ADU development, but it can unlock significant development potential in Simi Valley's residential neighborhoods.
Why Simi Valley Homeowners Choose Safeway Construction for ADUs
ADU demand in Simi Valley has grown significantly since 2022. That growth also brought in contractors who treat ADUs as volume work — assembly-line builds with minimal customization and no single point of contact.
We build ADUs the same way we build full kitchen and bathroom remodels. One project manager is assigned from permit to final inspection. We've been building across Ventura County — Simi Valley, Thousand Oaks, Moorpark, Camarillo, Oxnard — for over 20 years. Our 5.0-star Google rating reflects what that consistency produces. Licensed in California (#1066117), fully insured.
We manage the permit process end-to-end: pre-application review, plan check coordination with the City of Simi Valley Building and Safety Division at 2929 Tapo Canyon Road, school fee payment with SVUSD, and all inspections. You don't need to learn how to build an ADU. That's our job.
Ready to Build Your ADU?
Get a free estimate or book a consultation. We specialize in ADUs throughout Ventura County.
Frequently Asked Questions: ADU Cost in Simi Valley
How much does a detached ADU cost in Simi Valley in 2026?
A detached ADU in Simi Valley costs $140,000–$280,000 in 2026, depending on size and finishes. A 500 sq ft unit with standard finishes on a flat lot runs $140,000–$180,000. An 800 sq ft unit with premium finishes or on a sloped lot in Wood Ranch or Big Sky reaches $220,000–$280,000. Per-square-foot cost typically runs $280–$450/sq ft depending on finishes and site conditions.
What's the difference between an above-garage ADU and a detached ADU?
An above-garage ADU is built on top of an existing garage ($200K–$350K), combining privacy with minimal land footprint. A detached ADU is a standalone structure on the lot ($140K–$280K). Above-garage units work on smaller lots but require structural engineering for the existing garage. Detached units offer more design flexibility and slightly faster permitting. Both commands similar rental rates ($1,800–$2,400/mo).
Is a garage conversion the cheapest ADU option?
Yes. A garage conversion costs $60,000–$120,000 in Simi Valley — the lowest entry cost of any ADU type. The shell and foundation already exist, which eliminates a significant portion of new construction costs. You'll need to address parking replacement ($8,000–$20,000) and fire separation requirements during permitting. ROI is fastest with garage conversions: many homeowners use rental income to fund detached ADU projects later.
How long does it take to build an ADU in Simi Valley?
Total timeline: 7–9 months from design start to move-in. Breakdown: Design and engineering (4–8 weeks), permit application and review (6–10 weeks), construction (14–22 weeks). Garage conversions are fastest (10–18 weeks total). Detached ADUs on sloped lots can reach 22 weeks for construction alone.
Are school impact fees required for my ADU in Simi Valley in 2026?
ADUs 750 sq ft or smaller are exempt from school impact fees under California SB 543 (effective January 2026). This is a major savings — exemption saves $2,000–$4,500 on a typical ADU. Larger units pay the Simi Valley Unified School District fee of $4.14 per square foot. On an 800 sq ft ADU, this fee is $3,312. Many homeowners choose 750 sf vs. 850 sf to capture the SB 543 exemption.
How much rent can an ADU generate in Simi Valley?
A 1-bedroom ADU in Simi Valley rents for $1,800–$2,400 per month in 2026, depending on size, finishes, and whether it's detached. A 2-bedroom unit rents for $2,200–$2,800 per month. Long-term rental produces ~$24,000/year gross, typically nets $17,000–$18,000 after expenses. Occupancy rates for ADUs in Simi Valley run 95%+, making long-term rental more stable than short-term (Airbnb).
Does an ADU increase my property value in Simi Valley?
Yes. A permitted, rentable ADU in Simi Valley typically adds $150,000–$220,000 in appraised property value. Unpermitted ADUs add zero appraised value, cannot be legally rented, and create disclosure and financing complications at resale. ROI on a permitted ADU can exceed 100% when factoring in property appreciation over 5–7 years.
What is the difference between an ADU and a JADU?
An ADU is a fully independent dwelling unit — detached, attached, or a garage conversion — with its own entrance, kitchen, and bathroom. A JADU (Junior ADU) is 500 sq ft or less, created within the existing walls of the main house, and requires owner-occupancy of either the main home or the JADU. JADUs cost $35,000–$75,000 and are the lowest-cost ADU pathway. No parking required for JADUs.
How do I finance an ADU if I don't have enough home equity for a HELOC?
Several options: FHA 203(k) renovation loans allow up to 97% LTV on post-ADU appraised value, requiring only 3.5% down. Construction loans fund based on milestone draws. Cash-out refinance pulls a lump sum upfront. Credit union programs often have more flexible terms than traditional banks. HELOC requires 740+ credit and 80%+ home equity; FHA is more flexible. All require licensed contractor (we are) and appraisal.
What are the permit fees for an ADU in Simi Valley?
Typical total permit costs: Planning review $1,000–$2,000, building permit $250–$1,200 (based on project valuation), plan check $500–$1,500, inspections $300–$800. School fees: $0 for units ≤750 sq ft (SB 543), or $4.14/sq ft for larger units. Total soft costs (architectural plans, engineering, Title 24): $8,000–$20,000. Keeping your ADU at 750 sq ft saves $2,000–$4,500 in school fees.
Can I use my ADU as an Airbnb in Simi Valley instead of long-term rental?
Simi Valley regulations are lenient for short-term rentals in 2026. Income comparison: long-term rental nets $17,000–$18,000/year; Airbnb nets $15,000–$18,000/year after 45–55% operating expenses (cleaning, platform fees, turnover). Long-term requires less management and has more stable occupancy (95%+ vs. 60–65% for Airbnb). Regulations could tighten; long-term rental remains the safer long-term strategy.
What is SB 9 lot splitting and how does it relate to ADUs?
SB 9 allows homeowners to split residential lots without subdivision approval. Each resulting lot must be ≥1,200 sq ft and roughly equal in size. After a split, each lot can have a primary unit plus one ADU plus one JADU, potentially creating 4–6 units total on what was one property. 2026 updates reduced owner-occupancy timeline from 3 to 2 years. SB 9 is most valuable for owners with large lots who plan to maximize development potential.
How do property taxes increase when I build an ADU?
Property taxes are reassessed based on the appraised value added by the ADU (~$150,000–$220,000). Under California Proposition 13, the new tax is roughly 1% annually of the added value, or $1,500–$2,200/year. This is offset by rental income: a $180,000 ADU generating $24,000/year produces a 13.3% gross yield, and the property still appreciates 4–5% annually independent of the tax increase.
What is the payback period for an ADU investment in Simi Valley?
For a $200,000 detached ADU: rental income alone ($18,400/year net) yields a 10.9-year payback period. Adding property value appreciation (4–5% annually) accelerates payback to 7–8 years. Adding equity buildup from financed loans further accelerates to 5–6 years. The $150,000–$220,000 property value increase typically exceeds the build cost on resale after 5–10 years.
Do I need owner-occupancy to rent out my ADU in Simi Valley?
No. California eliminated owner-occupancy requirements for standard ADUs in 2022. You can rent both the main house and the ADU, live in the main house and rent the ADU, or vice versa. The only exception: Junior ADUs (JADUs) require owner-occupancy of either the main home or the JADU itself.
What happens if I build an ADU without permits?
Unpermitted ADUs add zero appraised value to your property, cannot be legally rented, and create major disclosure issues at resale. Mortgage lenders and appraisers will not count unpermitted units. Fines can run $500/day, and the city can issue removal orders. Permit costs are a small fraction of the ADU's value — never skip permitting.
What's Your ADU Worth? Find Out in 2 Minutes.
If you're in Simi Valley, Thousand Oaks, Moorpark, or anywhere in Ventura County, the fastest way to get a real number is our free AI estimator at our free cost calculator. Answer 5 questions about your property and your ADU goals — get a price range you can actually plan around. No sales pitch, no contractor visit required.
Ready to move beyond the estimate? Call us at (805) 222-6544 or use the site to schedule a free consultation. We'll review your lot, your utility situation, and your city's specific requirements — and give you a fixed-price proposal before any work begins.
Safeway Construction — Simi Valley's ADU builders. 20+ years in Ventura County. CA Lic #1066117.