How much does an ADU cost in Orange County?
Current L Square prefab ADU model prices, the site and utility conditions that shape a quote, and the scope review needed before final pricing. CSLB #1095476.
ADU cost in Orange County depends on the project type, size, design tier, existing conditions, utilities, access and finish scope. L Square currently has fixed prices configured for six prefab models from 600 to 1,200 square feet. For garage conversions, attached ADUs, custom detached builds and JADUs, the ADU cost calculator below gives a typical planning range from our current per-square-foot rates — $150–$300/sq ft for garage conversions, $260–$400/sq ft attached, $270–$380/sq ft detached — and final pricing always follows a site and scope review.
Pricing reviewed August 12, 2026. Model prices are the current configured fixed model price before applicable site-specific add-ons. Sewer, electrical, demolition, grading, access, permit and other property conditions may change the final quote. Final pricing requires a site and scope review.
Current configured prefab model prices
The rows below are the only ADU model prices currently configured for L Square. They are model prices, not final project totals. Site-specific add-ons and jurisdiction requirements are reviewed before a final quote.
| Model | Size | Beds/baths | Current configured price |
|---|---|---|---|
| Model 600 | 600 sq ft | 2 bed / 1 bath | $180,000 |
| Model 800A | 800 sq ft | 2 bed / 2 bath | $240,000 |
| Model 800B | 800 sq ft | 2 bed / 2 bath | $240,000 |
| Model 1000A | 1,000 sq ft | 3 bed / 2 bath | $295,000 |
| Model 1000B | 1,000 sq ft | 3 bed / 2 bath | $295,000 |
| Model 1200 | 1,200 sq ft | 3 bed / 2 bath | $354,000 |
ADU cost calculator — Orange County (2026)
For the types without a configured fixed price, pick a type and size to see the typical planning range at our current per-square-foot rates. It is a planning tool, not a quote — the site factors below decide where a real project lands.
▶Where the money goes
Line-item budgets are itemized in our garage conversion guide.
Planning ranges, not quotes — rates reviewed August 12, 2026. Final pricing requires a site and scope review of the conditions below.
Why one property quote differs from another
A model price is only one part of a real ADU budget. The final number depends on the property, the utility route, the design package, outside-agency review and the finish scope. That is why L Square reviews the site before issuing final pricing.
- Electrical service and panel capacity
A new dwelling needs safe electrical capacity. The existing service, main panel, subpanel options and utility involvement can affect the scope.
- Sewer route and connection conditions
Distance to the connection, gravity flow, trenching access and existing line condition can change how the ADU is connected.
- Utility metering
Some projects use shared utilities, some use submeters, and some require separate service coordination. The right answer depends on the property and local requirements.
- Demolition and existing-structure condition
Old garages, slabs, sheds, concrete, framing and roof conditions can affect the work required before the new unit can be built or converted.
- Lot slope, drainage and foundation scope
Flat lots are simpler. Sloped lots, drainage constraints, retaining needs and foundation design can materially change the construction plan.
- Construction access
Side-yard width, staging space, equipment access and concrete placement affect labor and logistics.
- Finish and appliance selections
Cabinets, counters, flooring, tile, fixtures, appliances and HVAC choices should be specified before comparing bids.
- Permit, school, utility and outside-agency review
City permit review, school fees, utility coordination and outside-agency conditions may apply. Keep those items in the written scope instead of assuming they are included.
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State rules and financing notes to verify before budgeting
California ADU rules are governed by state law and local implementation. Start with the official HCD ADU handbook, then confirm the local maximum and submittal requirements for the property.
- Under Government Code section 66321, local maximum rules generally may not be below 850 square feet, or 1,000 square feet for an ADU with more than one bedroom. An 800-square-foot pathway is protected under specified height, setback and other standards. Verify the local maximum for the property.
- Under Government Code section 66313(d) and section 66333(d), a JADU is no more than 500 square feet and must be contained entirely within a proposed or existing single-family residence. Enclosed uses within the residence, including attached garages, count as part of the residence. Efficiency kitchen requirements, sanitation provisions, a deed restriction and owner-occupancy rules apply where required by current law. Confirm details against HCD guidance and the local agency.
- Some FHA scenarios may consider 75% of eligible ADU rent, subject to appraisal, lease, transaction, occupancy, income-cap and underwriting rules. Review HUD Mortgagee Letter 2023-17 and confirm with a licensed lender before relying on rental income for qualification.
How to get a number you can trust
A reliable quote starts with a site review, then a written scope that separates the configured model from site-specific add-ons, permit and agency requirements, utility work, finish selections and assumptions. That is the document you can compare against other bids.
If you want to compare ADU paths before a site visit, these guides explain the scope differences without pretending every property has the same price:
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