How much an ADU costs in Simi Valley
What an ADU costs in Simi Valley in 2026: dated competitor ranges, City ADU permit fees, the 750 and 500 sq ft fee thresholds, and grant scam warnings.
Short answer: a garage conversion in Simi Valley is listed by one competitor's published calculator at about $130,000 to $180,000 (that company says its figures are planning budgets, not market averages), and a new detached unit between about $240,000 and $485,000 depending on size. Those are a competitor's published ranges, dated September 16, 2026. Aguila does not publish its own prices yet, because every lot prices differently.
The construction contract is only part of the bill. City permit fees, school fees, utility work and design also count, and two of the fee rules contradict each other in ways most cost pages miss. This page lays out each piece with its source and date.
Published construction ranges
The most recent dated Simi Valley ranges come from Safeway Remodel, a Simi Valley competitor, with a factual update stamped September 16, 2026. We show them so you can test bids against something public. They are not Aguila quotes.
| Project | Published range | Active construction |
|---|---|---|
| Garage conversion, 400 sq ft, 1 bed / 1 bath | $130,000 to $180,000 | About 4 to 5 months |
| Detached ADU, 600 sq ft | $240,000 to $330,000 | About 6 to 11 months |
| Detached ADU, 1,000 sq ft | $355,000 to $485,000 | About 6 to 11 months |
City of Simi Valley permit fees
The City's Summary of Service Charges effective July 1, 2024 (FY2024-25) has its own Accessory Dwelling Unit line in the new construction table. For standard wood-frame construction (types III-B, IV and V-B), combined plan check and inspection runs as below. The schedule adds 8 percent surcharges each for plumbing, mechanical and electrical, and an expedited single-cycle plan check costs double the plan check fee. Fees are usually adjusted each July, so confirm the current schedule.
- Pre-application review: $438.33.
- New Dwelling Fee per unit: $504.78 (one bedroom), $753.10 (two bedrooms). Ask Building & Safety whether it applies to your ADU.
| ADU size | Plan check + inspection |
|---|---|
| 500 sq ft | $3,009 |
| 750 sq ft | About $3,280 ($3,009 plus $108.23 per added 100 sq ft) |
| 1,000 sq ft | $3,551 |
| 1,200 sq ft | About $4,233 ($3,551 plus $340.74 per added 100 sq ft) |
The 750 vs 500 square foot contradiction
Two fee thresholds apply, and they are different. Under Government Code 66311.5, an ADU of 750 square feet of interior livable space or less pays no impact fees to the City, special districts or water companies; above 750, impact fees are charged in proportion to the ADU's size compared to the main house. School districts are separate: HCD's handbook says they may charge fees on ADUs larger than 500 square feet, and units under 500 square feet are exempt.
So a 700 square foot ADU can owe school fees but no city impact fees. A 480 square foot unit owes neither. Sizing a unit just under 500 or 750 square feet is one of the few design choices that cuts soft costs outright.
Grants, scams and paying for plans
The CalHFA ADU Grant, up to $40,000 for pre-development and closing costs, is not taking new money: CalHFA's page says the latest round has been fully allocated (update dated December 28, 2023). CalHFA also warns that anyone offering to help you get an ADU grant is running a financial scam.
CSLB's consumer alert covers the other common trap. Be careful about paying for 'plans' or 'permits' before work starts: ask for an accounting of the plan cost or call the engineer or architect, and check permit costs with the building department yourself.
Questions homeowners ask
What is the cheapest way to add an ADU in Simi Valley?
A JADU inside the house, then a garage conversion. Both reuse an existing foundation and roof, and a JADU of 500 square feet or less pays no impact fees or school fees.
How much are ADU permit fees in Simi Valley?
On the City's schedule effective July 1, 2024, combined plan check and inspection for a wood-frame ADU runs about $3,009 at 500 square feet and $3,551 at 1,000 square feet, plus 8 percent trade surcharges. School fees and utility work are extra.
Does a 700 square foot ADU pay impact fees?
No city impact fees: the exemption covers ADUs of 750 square feet or less. It can still owe school district fees, because that exemption stops at 500 square feet.
Is the $40,000 CalHFA ADU grant still available?
Not as of CalHFA's current page, which says the latest round is fully allocated. Treat anyone offering to get you that grant as a scam, per CalHFA's own warning.
Why don't you list your own prices?
Because a 400 square foot unit on a flat Texas Tract lot and the same unit on a sloped Wood Ranch pad in a fire zone are different jobs. Paul prices from a site visit, in writing, and the payment schedule follows the work.
Sources
Facts on this page last verified: .
- Competitor's published range: Safeway Remodel, ADU cost in Simi Valley (factual update September 16, 2026): https://www.safewayremodel.com/blog/adu-cost-simi-valley-2026 (2026-10-05)
- City of Simi Valley Summary of Service Charges, effective July 1, 2024 (FY2024-25): https://simivalleylibrary.org/wp-content/uploads/2025/02/CityofSimiValley_FeeSchedule2025.pdf (2026-10-05)
- HCD ADU Handbook, updated for law in effect January 1, 2026: https://www.hcd.ca.gov/sites/default/files/docs/policy-and-research/adu-handbook-update.pdf (2026-10-05)
- CalHFA ADU Grant Program status and scam alert: https://www.calhfa.ca.gov/adu/ (2026-10-05)
- CSLB Consumer Alert: Don't Pay Too Much Money Upfront (ADU payments): https://www.cslb.ca.gov/Resources/PressReleases/2024/ADU-payments.FINAL.pdf (2026-10-05)
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