How much does an ADU cost in California in 2026?

By Jarrod·Editor·Last verified April 2026

Most California homeowners pay $100,000–$400,000 to build an ADU, all-in. Garage conversions start around $40k; high-end detached builds in the Bay Area can top $500k. Type, region, size, and finish level drive the spread — not which contractor you pick.

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How to read these numbers. Ranges are scoping estimates from a regression of eight published 2026 builder pricing sources, applied to a regional multiplier. They cover typical design, engineering, building permits, materials, labour, and contractor margin on a flat lot with standard utilities. They do not separately model site work, utility upgrades, above-baseline impact fees, financing carry, or fire-zone / coastal / hillside overlays — any of which can shift a real quote 10–40%. Full methodology →

Cost by ADU type

Each ADU type has its own cost profile. Garage conversions are the cheapest (existing structure); detached new builds are the most expensive (full foundation + utilities).

All-in design-build cost by ADU type, 2026 dollars, Los Angeles prices, typical size for each type
ADU type	All-in cost, low to high
Garage ConversionCheapest path. ~400 sqft typical. 4–8 month builds.	$36,000–$96,000typical $60,000$90–$240 per sqft
Junior ADU (JADU)Within existing footprint. ≤500 sqft. Owner-occupancy rules apply to some JADUs.	$36,000–$96,000typical $60,000$90–$240 per sqft
Basement ConversionOlder homes only. Waterproofing + egress drive cost.	$63,000–$168,000typical $105,000$105–$280 per sqft
Attached ADU5–15% cheaper than detached. Shared wall.	$105,000–$266,000typical $168,000$150–$380 per sqft
Prefab / ModularFaster install. Cost certainty. Lot constraints apply.	$81,000–$216,000typical $135,000$135–$360 per sqft
Detached ADUMost flexible. Highest resale value. 12–18 months.	$135,000–$360,000typical $225,000$180–$480 per sqft

Each bar runs from the low to the high estimate, on a scale that starts at $0. The dark mark is the typical cost.

Cost by region

Per-square-foot pricing varies widely by California region. Bay Area runs ~30% above LA baseline; Central Valley runs ~25% below.

Detached ADU, about 750 sqft: all-in design-build cost by region, 2026 dollars
Region	All-in cost, low to high
Bay Area (SF, Oakland, San Jose)1.30× LA prices	$175,500–$468,000typical $292,500$234–$624 per sqft
Central Coast (Santa Barbara, SLO)1.05× LA prices	$141,750–$378,000typical $236,250$189–$504 per sqft
Los Angeles + Orange County1.00× LA prices	$135,000–$360,000typical $225,000$180–$480 per sqft
San Diego region0.95× LA prices	$128,250–$342,000typical $213,750$171–$456 per sqft
Sacramento region0.85× LA prices	$114,750–$306,000typical $191,250$153–$408 per sqft
Inland Empire0.85× LA prices	$114,750–$306,000typical $191,250$153–$408 per sqft
Central Valley (Fresno, Bakersfield)0.75× LA prices	$101,250–$270,000typical $168,750$135–$360 per sqft

Each bar runs from the low to the high estimate, on a scale that starts at $0. The dark mark is the typical cost.

What's included in these numbers

All-in design-build pricing covers the four main cost layers:

Architecture & engineering — typically 5–10% of total ($10k–$30k)
Permits & impact fees — typically 5–15% ($8k–$35k including soils, plan check, school fees)
Construction labor & materials — typically 70–80% ($150k–$300k+)
Soft costs — utility connections, site prep, project management — typically 5–10%

What can push you 20–40% higher

Sloped lots requiring engineered foundations ($25k–$80k)
Long utility runs from main house to ADU ($15k–$50k)
Tree-protection or hillside review processes (3–6 weeks delay + arborist fees)
Custom architectural features beyond catalog options
Difficult site access (no driveway for materials)
Impact fees on ADUs over 750 sqft (waived for smaller ADUs)

How much does an ADU cost in California in 2026?

Cost by ADU type

Cost by region

What's included in these numbers

What can push you 20–40% higher

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