The first question about an ADU is usually price, but the honest answer starts with build type. A garage conversion reuses a slab, walls, and roof. A junior ADU is carved out of the existing home and capped at 500 square feet. A new detached unit needs foundations, utilities, and a full plan set. Oct 2026 market guides price those builds very differently, and the ranges below are third-party market guides, not prices or quotes from Radiant Renovations Co.
Guide ranges by build type
For detached ADUs, ADU Verified's 2026 guide gives $200,000 to $400,000, Shulmen's 2026 guide gives $250,000 to $450,000 at $400 to $650 per square foot, and Construction by Maya's syndicated 2026 ranges run from $180,000 to $260,000 for a 500-square-foot unit to $350,000 to $550,000 or more for a 1,000 to 1,200-square-foot unit. For garage conversions, ADU Verified gives $100,000 to $220,000, Shulmen gives $130,000 to $220,000 over 4 to 6 months of construction, and Construction by Maya gives $90,000 to $160,000 for a 400 to 500-square-foot conversion. Attached ADUs are put at $260,000 to $380,000 by ADU Verified, junior ADUs at $80,000 to $175,000 across the guides, and prefab or modular units at $150,000 to $300,000. Presenting those as one ADU price would hide the build type, the size, and the site, which are exactly what decide the cost.
The line items that move the total
- Utilities. Sewer and water extensions, panel upgrades, and service capacity are repeatedly cited as surprises, with guide figures for sewer and water extensions and panel upgrades varying by distance and existing capacity. Check both before budgeting finishes.
- Site and soils. Hillside lots, steep slopes, expansive soils, and deep or pier foundations add guide premiums that grow with unit size, and grading and fire-access review can add time as well as cost.
- Historic review. An ADU in an HPOZ still faces exterior design review even though state law makes the ADU itself ministerial, and guides cite added weeks and historic-compatible finish costs for HPOZ sites.
- Soft costs. Plans, engineering, permits, and fees sit on top of construction in every guide, and a pre-approved LADBS standard plan can shorten plan check without waiving the building permit or site-specific review.
- Fees and thresholds. Guides describe impact-fee relief for smaller units and fee proportionality for larger ones, but fee practice must be confirmed with LADBS for the parcel and the unit size before any figure is relied on.
Rules that shape the budget before finishes do
California ADU law sets floors a city cannot go below, including approval of an ADU of up to 800 square feet with 4-foot side and rear setbacks regardless of lot coverage or floor-area limits, a ministerial decision rather than a discretionary hearing, and a decision clock for a complete application. The City of Los Angeles adds its own ordinance, LAMC 12.22 A.33, and its LADBS Standard Plan Program. None of that removes parcel checks: zoning, HPOZ status, hillside area, and Very High Fire Hazard Severity Zone status are checked per address, and the hillside-plus-fire-zone two-map test can close the door on a site that looks feasible from the street. See our ADU construction page, our garage conversion page, and our room additions page for how those paths differ, and read the permitting companion post in this blog for the stalls that most often delay approval.
Frequently Asked Questions
What do Oct 2026 guides say a detached ADU costs in Los Angeles?
Guides range from about $180,000 to $550,000 or more depending on size, site, and finishes. These are third-party market guides, not quotes, and they must not be collapsed into one average.
Why is a garage conversion cheaper in the guides than a detached ADU?
Because it reuses the slab, walls, and roof that already exist. Full bathroom and kitchen work, permits, and utility upgrades still push a conversion toward the top of its guide range.
Does a pre-approved LADBS plan mean my ADU is approved?
No. A standard plan is pre-reviewed for building-code compliance, but the building permit, site fit, soils, utilities, fire, and HPOZ review still apply to the parcel.
What should I check before budgeting an ADU?
Zoning, setbacks, HPOZ status, hillside area, fire-zone status, sewer and water capacity, and panel capacity. Those parcel checks decide feasibility before finishes are priced.
Get help with renovations in Los Angeles
If you are planning an ADU project in the City of Los Angeles, start with a conversation about scope, permits, and sequence before you commit to finishes or a start date.
Call Radiant Renovations Co. at +1 (424) 337-6597. The business is open 24 hours, 7 days a week, and is located at 352 W Martin Luther King Jr Blvd, Los Angeles, CA 90037.