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).

Cost by region

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

Region	Multiplier vs LA	Detached ADU example (750 sqft)
Bay Area (SF, Oakland, San Jose)	1.30×	$175,500–$468,000
Central Coast (Santa Barbara, SLO)	1.05×	$141,750–$378,000
Los Angeles + Orange County	1.00×	$135,000–$360,000
San Diego region	0.95×	$128,250–$342,000
Sacramento region	0.85×	$114,750–$306,000
Inland Empire	0.85×	$114,750–$306,000
Central Valley (Fresno, Bakersfield)	0.75×	$101,250–$270,000

All-in design-build estimates for a typical 750 sqft detached ADU in 2026 dollars.

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%