Why does adu construction cost vary by city?

Local labor rates, permit timelines, and demand differ across Southern California. Each city in our guides applies its own cost multiplier to the regional baseline, so a adu construction in a coastal premium market costs more than the same scope inland.

Is the price worth it — and how do I avoid overpaying?

Get at least three written bids for the identical scope, make finishes allowance-based, and check that permits and overhead-and-profit are shown as their own lines. Keystone matches you with up to 3 vetted contractors and will review a bid you already have.

ADU Construction Cost in Southern California (2026)

Q: How much does a adu construction cost in Southern California in 2026?

A mid-size adu construction typically runs $90k–$180k at the LA County baseline. Small projects start around $60k; large or high-end work can reach $450k or more. Orange County runs slightly above this and San Bernardino County below.

A mid-size adu construction typically runs $90k–$180k at the LA County baseline ($300–$500 per sq ft). Small projects start around $60k; large or high-end work can reach $450k or more.

Pricing varies across Southern California — Orange County runs a bit above the LA baseline and San Bernardino County below. Compare by county and city below.

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ADU Construction Cost by Size

Southern California baseline ranges (LA County = 1.0× baseline). Individual counties and cities vary — see below.

Size	Type	Range	Low	High
Small	JADU / studio	150–400 sq ft	$60k	$130k
Medium	1-bed garage conversion	400–600 sq ft	$90k	$180k
Large	Detached 2-bed	800–1,200 sq ft	$250k	$450k

ADU Construction Cost by County

Los Angeles County

$90k–$180k

mid-size · 1.00× baseline

See LA County city-by-city

Orange County

$95k–$189k

mid-size · 1.05× baseline

See OC city-by-city

San Bernardino County

$77k–$153k

mid-size · 0.85× baseline

See SB County city-by-city

ADU Construction Cost by City

What Affects ADU Construction Cost?

ADU type (JADU vs attached vs detached)
Site prep and grading
Utility connections
CA Title 24 energy compliance
City ADU permit timeline

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ADU Construction Cost FAQs

Keep exploring

Compare other project costs, drill into adu construction by area, or read our guides.

Other project cost guides

ADU Construction by area

Renovation guides

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