When your garage should become an ADU
When a Simi Valley garage should become a rentable ADU: no replacement parking, no size cap, no sprinkler trigger, and the partial-garage rule now in flux.
A garage becomes an ADU when it gets complete independent living facilities: a kitchen, a bathroom, a place to sleep and its own exterior entrance. That is the version you can rent to a tenant, or give to a relative as a separate home.
Garage ADUs are built through our sister site, simivalleyaduconstruction.com, which covers detached, attached and garage ADUs in full. This page explains why the ADU route deserves a look for a garage, and what state law gives you that a plain living-space conversion does not.
Five state rules that favor a garage ADU
Simi Valley's own Ordinance No. 1349 already allowed existing living area converted within the existing structure to become an ADU without any size limit, as quoted in HCD's October 29, 2025 findings.
| Rule | What it means for your garage | Code |
|---|---|---|
| No replacement parking | The City cannot make you replace the garage spaces you convert | Gov. Code 66314(d)(11) |
| No size cap on a straight conversion | A unit built inside the existing walls is not held to local ADU size limits | Gov. Code 66323(a)(1), (b) |
| 150 square feet for access | The structure can grow up to 150 square feet only to fit ingress and egress | Gov. Code 66323(a)(1)(A) |
| No sprinkler trigger | Sprinklers are required only if the main house requires them | Gov. Code 66323(d); 66314(d)(12) |
| No owner-occupancy rule | You do not have to live on the property to rent the ADU | Gov. Code 66315 |
Simi Valley's partial-garage rule, and why it is changing
Ordinance No. 1349 says that when an attached garage holding a house's required parking is partially converted to an ADU, the remaining space stays parking if it is physically usable and at least 12 feet by 20 feet; otherwise it is used for storage or another non-habitable use. Treat that rule as superseded pending Ordinance No. 1373, the City's replacement.
The reason: on October 29, 2025 HCD issued 19 findings that Ordinance 1349 conflicts with state ADU law, among them that it counted garages as living area (the state definition excludes garages) and cited repealed code sections instead of Government Code sections 66310 to 66342. The City had until November 28, 2025 to respond. Until the new ordinance governs, confirm the partial-garage requirement with the City before drawing.
Fees and timing for a garage ADU
An ADU with 750 square feet of interior livable space or less is exempt from impact fees, and a converted ADU is not counted as a new residential use for water and sewer connection fees unless it is built along with a new home (HCD ADU Handbook, March 2026, Gov. Code 66311.5). A 400 square foot garage, the size Safeway Remodel uses in its September 16, 2026 cost example, falls well under that line.
Once the application is complete, the City must approve or deny it within 60 days when a house already stands on the lot (Gov. Code 66317). A denial must arrive with a full set of comments explaining how to fix the application.
Questions homeowners ask
Should my garage be an ADU or an added bedroom?
If anyone outside your household might live there, or you want rent income, make it an ADU. If it stays part of your home, a living-space conversion is simpler. Parking often decides it: the ADU route removes the replacement-parking requirement and the living-space route does not.
Can I list a garage ADU as a short-term rental?
Not if it was approved as a conversion unit under Gov. Code 66323. Rentals of those units must be for terms longer than 30 days (HCD ADU Handbook, March 2026).
Do I have to live on the property to rent the ADU?
No. State law bars owner-occupancy requirements for ADUs (Gov. Code 66315). The exception is a junior ADU that shares sanitation with the main house.
Why send me to another site for the ADU?
A full ADU is a different project with its own rules, fees and design questions, and simivalleyaduconstruction.com walks through all of them. Same company, same license, same phone number.
Sources
Facts on this page last verified: .
- California HCD, Accessory Dwelling Unit Handbook, March 2026: https://www.hcd.ca.gov/sites/default/files/docs/policy-and-research/adu-handbook-update.pdf (2026-10-05)
- HCD findings on Simi Valley ADU Ordinance No. 1349, letter of October 29, 2025: https://www.hcd.ca.gov/sites/default/files/docs/policy-and-research/ordinance-review-letters/simi-valley-adu-findings-102925.pdf (2026-10-05)
- City of Simi Valley, second reading of Ordinance No. 1349, staff memo of June 5, 2023: https://simivalley.granicus.com/MetaViewer.php?view_id=5&clip_id=2792&meta_id=204582 (2026-10-05)
- Safeway Remodel, ADU cost in Simi Valley (competitor-published, factual update September 16, 2026): https://www.safewayremodel.com/blog/adu-cost-simi-valley-2026 (2026-10-05)
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