How much does a 1-bedroom ADU cost to build in Los Angeles County?

A 1-bedroom ADU in LA County typically ranges 450–600 sq ft and costs $180,000–$350,000 total for a detached unit (all-in: construction, permits, design, utilities). Garage conversions for the same size run $80,000–$180,000. The wide range reflects LA County's varied construction costs by submarket: coastal areas (Malibu, Pacific Palisades) and hillside lots with limited access are significantly more expensive than the San Fernando Valley flatlands.

What are the permit fees for an ADU in LA County?

LA County permit fees vary by ADU size and type but typically run $5,000–$20,000 total for all required permits (building, electrical, plumbing, mechanical). The building permit fee is typically calculated as a percentage of valuation (1–3% of project value). School fees apply in many unincorporated areas: approximately $4.08/ft² for residential in 2024. Water and sewer capacity/connection fees can be substantial ($5,000–$20,000) depending on the local water authority (LA DWP, Las Virgenes, etc.).

Is a garage conversion or new detached ADU cheaper in LA County?

Garage conversions are significantly cheaper — typically 40–60% of the cost of a new detached ADU — because the foundation, floor slab, and roof structure already exist. A typical LA County 2-car garage conversion (400–440 ft²) costs $70,000–$140,000 all-in vs. $180,000–$300,000 for an equivalent-size new detached build. The tradeoff: garage conversions often require adding insulation, HVAC, plumbing, and egress windows, and you lose parking (LA County requires replacement parking in most circumstances).

Can I build an ADU myself in LA County to save money?

Owner-builder permits are available in LA County, allowing homeowners to act as their own general contractor. This can save 15–25% on GC overhead and profit. However, you still need licensed subcontractors for electrical, plumbing, and HVAC work. Owner-builder permits require the homeowner to live in the unit for a specified period after construction and restrict the sale of the property. The complexity of LA County plan check requirements and Title 24 energy compliance makes self-managing an ADU project challenging without prior construction experience.

Los Angeles County ADU Cost Calculator: Construction Budget and Total Project Cost

Estimate ADU construction cost in Los Angeles County — from base build cost per square foot through design, permits, utilities, and contingency to total project budget.

Related Calculators

Los Angeles County ADU Cost Calculator
Estimate a Los Angeles County ADU budget from unit size, construction cost, design, permits, utility work and contingency.

How LA County ADU Costs Are Estimated

An ADU (Accessory Dwelling Unit) project cost has four main components:

Total project cost = Base construction + Design/engineering + Permits/fees + Utilities/site work + Contingency

Base construction cost = ADU area (ft²) × Construction cost per ft²

2024 Construction Cost Ranges — Los Angeles County

ADU Type	Cost per ft²	Notes
Garage conversion (ADU)	$150–$250/ft²	Lowest cost; uses existing structure
Junior ADU (JADU, <500 ft²)	$200–$350/ft²	Interior conversion
Detached ADU (new construction)	$300–$500/ft²	Full new build
Prefab / modular ADU	$200–$400/ft²	Factory-built, faster timeline
Above-garage ADU	$350–$600/ft²	Structural complexity
Two-story ADU	$350–$550/ft²	Higher foundation and framing costs

Soft Cost Breakdown

Cost Category	Typical Range
Architectural design	$8,000–$25,000
Structural engineering	$2,000–$8,000
Title 24 energy compliance	$1,000–$3,000
Surveys / soil report	$2,000–$5,000
LA County plan check fees	$3,000–$15,000
Building permit fees	$5,000–$20,000
School fees (Mello-Roos areas)	$1,500–$5,000
Water/sewer capacity fees	$5,000–$20,000
Utility connections (SCE, SoCalGas)	$2,000–$10,000

Worked Example — 600 ft² Detached ADU

Line Item	Low	High
Base construction (600 ft² × $350–$450/ft²)	$210,000	$270,000
Design and engineering	$12,000	$22,000
Permits and plan check	$8,000	$18,000
Utilities and site work	$10,000	$25,000
15% contingency	$36,000	$50,250
Total estimated budget	$276,000	$385,250

LA County ADU Program Notes

By-right approval: ADUs under 1,200 ft² meeting setback and height limits may be approved ministerially (no discretionary review) under AB 68 / SB 9.
Impact fee exemption: ADUs under 750 ft² are exempt from many LA County impact fees.
Owner-occupancy waiver (2020–2025): The owner-occupancy requirement for ADUs was suspended; verify current rules at time of application.
Pre-approved ADU plans: LA County offers pre-approved ADU plan sets ($10,000–$30,000 savings in design fees).

Frequently Asked Questions

How much does a 1-bedroom ADU cost to build in Los Angeles County?: A 1-bedroom ADU in LA County typically ranges 450–600 sq ft and costs $180,000–$350,000 total for a detached unit (all-in: construction, permits, design, utilities). Garage conversions for the same size run $80,000–$180,000. The wide range reflects LA County's varied construction costs by submarket: coastal areas (Malibu, Pacific Palisades) and hillside lots with limited access are significantly more expensive than the San Fernando Valley flatlands.
What are the permit fees for an ADU in LA County?: LA County permit fees vary by ADU size and type but typically run $5,000–$20,000 total for all required permits (building, electrical, plumbing, mechanical). The building permit fee is typically calculated as a percentage of valuation (1–3% of project value). School fees apply in many unincorporated areas: approximately $4.08/ft² for residential in 2024. Water and sewer capacity/connection fees can be substantial ($5,000–$20,000) depending on the local water authority (LA DWP, Las Virgenes, etc.).
Is a garage conversion or new detached ADU cheaper in LA County?: Garage conversions are significantly cheaper — typically 40–60% of the cost of a new detached ADU — because the foundation, floor slab, and roof structure already exist. A typical LA County 2-car garage conversion (400–440 ft²) costs $70,000–$140,000 all-in vs. $180,000–$300,000 for an equivalent-size new detached build. The tradeoff: garage conversions often require adding insulation, HVAC, plumbing, and egress windows, and you lose parking (LA County requires replacement parking in most circumstances).
Can I build an ADU myself in LA County to save money?: Owner-builder permits are available in LA County, allowing homeowners to act as their own general contractor. This can save 15–25% on GC overhead and profit. However, you still need licensed subcontractors for electrical, plumbing, and HVAC work. Owner-builder permits require the homeowner to live in the unit for a specified period after construction and restrict the sale of the property. The complexity of LA County plan check requirements and Title 24 energy compliance makes self-managing an ADU project challenging without prior construction experience.

Last updated 8/9/2026