AXE CONSTRUCTION INC · CSLB Lic #1069232 · Class B General Building · Licensed and insured since 2020 · Verify our license
Published 2026 benchmarks put the cost to build an ADU in Los Angeles at roughly $100,000 to $225,000 for a garage conversion and $150,000 to $400,000 or more for a detached new construction ADU, or about $250 to $450 per square foot, before soft costs and site work. This page explains where those numbers come from, what city fees really cost, and what moves the final cost on your lot.
AXE CONSTRUCTION INC · CSLB Lic #1069232 · Class B General Building
There is no single number, because an accessory dwelling unit is new construction on a specific lot with specific utilities. What exists are published benchmarks that agree with each other more than most homeowners expect:
| Source | What it measures | Figure |
|---|---|---|
| UC Berkeley Terner Center for Housing Innovation, statewide ADU owner survey | Median construction cost reported by California ADU owners (2020–2021) | About $150,000, or roughly $250 per square foot, which now reads as the floor of the Los Angeles range |
| Published 2026 Los Angeles contractor and designer cost guides | Typical all-in construction cost by ADU type on standard lots | Garage conversion $100,000–$225,000 ($250–$450 per square foot); detached new construction $150,000–$400,000+ ($300–$450 per square foot); small or hillside units $450–$600+ per square foot |
| City of Los Angeles published fee examples (cited by local guides) | Plan check and permit fees on two sample units | About $1,045 for a 400-square-foot garage conversion; about $8,448 for a 1,200-square-foot detached unit, before school and sewer fees |
Read together: a garage conversion in Los Angeles is a six-figure project, a detached unit is a bigger one, and the per-square-foot number falls as the unit gets larger because the kitchen, the bathroom and the utility hookups are fixed costs. Everything below is about why.
The least expensive route for most Los Angeles homeowners because the slab, walls and roof of the existing garage are reused. What you pay for is the conversion to living space: a new floor assembly or moisture barrier, insulation, egress windows, a wall where the garage door was, plumbing saw-cut under the slab, electrical, a mini-split, finishes and the permit. A one-car garage becomes a studio; a two-car garage becomes a one- or two-bedroom. Published guides: $100,000 to $225,000. Our garage conversion page covers the code requirements.
A standalone unit built from the ground up: foundation, framing, roof, utilities trenched from the main house, and the full set of interior systems. More money than a conversion, but full control of layout, ceiling height and windows, and the most privacy for tenants or family. Published guides: $150,000 to $400,000 or more, with two story units and hillside lots at the top. Our ADU page covers detached and two-story units.
Shares a wall and often utilities with the main house, which usually makes it cheaper per square foot than a detached unit. The trade is privacy, and the design has to respect the main house's structure and the fire separation between units.
Up to 500 square feet carved out of the existing home, with its own entrance and an efficiency kitchen. The lowest cost of all because no new structure is built, and it can be added alongside a full ADU on the same lot under California state law.
Permit costs are smaller than most homeowners fear and more layered than they expect. For an ADU permit in the City of Los Angeles you pay LADBS plan check fees and a building permit fee based on the project valuation, plus separate electrical, plumbing and mechanical permits. Three rules set by California state law decide the rest:
Published 2026 guides put total city fees for a typical Los Angeles ADU at roughly $5,000 to $15,000, with small garage conversions at the bottom and large detached units at the top. In unincorporated LA County and in other cities, each building department sets its own schedule, and several offer a pre approved plan program that shortens review. Unpermitted work costs more than any fee: it cannot be legally rented, counted by an appraiser, or sold without correction.
Two numbers answer the question for most Los Angeles homeowners. First, rental income: a permitted, legal unit with its own address rents as a studio, one-bedroom or two-bedroom, and in most Los Angeles neighborhoods that income covers the monthly payment on construction financing with room to spare over a long hold. Second, property value: appraisers and buyers count permitted living space, and an ADU adds significant value to the lot. The other reasons, multigenerational living and a home office with its own entrance, do not show up on a spreadsheet and are just as common.
One honest drawback: an ADU changes how the backyard is used and adds a second set of utilities, maintenance and, for a rental, a landlord's responsibilities. We design around the backyard and say so to homeowners who are on the fence.
Most construction disputes start in the contract, not on the job site. I went to law school before I became a contractor, so every agreement we write spells out scope, allowances, change orders and the schedule in plain terms. When nothing is left vague, there is nothing to argue about later.
We partner with construction lending companies to offer financing options. Learn more about Axe Construction, or verify our license at cslb.ca.gov.
Converting an existing garage or carving a junior ADU out of the main house. Both reuse the structure you already own, skip the foundation, framing and roof, and usually stay under the 750-square-foot line that exempts them from impact fees. A single-story detached unit under 800 square feet is the next least expensive, because it avoids most local design rules.
Using the published 2026 benchmarks on this page, a 500-square-foot detached ADU runs roughly $150,000 to $225,000 at $300 to $450 per square foot, before soft costs and site work, and small units sit at the high end of the per-foot range because the kitchen, bathroom and utility hookups are fixed costs spread over fewer feet. A 500-square-foot garage conversion costs less.
At the published $300 to $450 per square foot range, an 800-square-foot detached unit runs roughly $240,000 to $360,000 in hard construction cost. An 800-square-foot unit is still exempt from most local design rules under state law, but it is over the 750-square-foot impact-fee line, so city fees rise.
Roughly $360,000 to $540,000 in hard cost at the published range, and the per-foot number usually falls at this size because fixed costs are spread wider. A 1,200-square-foot detached unit is the largest the City of Los Angeles allows, pays impact and school fees, and often needs an electrical service upgrade and a second bathroom.
Attached is usually cheaper per square foot because it shares a wall, a roof line and often utilities with the main house. Detached costs more but gives tenants and family full privacy and gives the design freedom. A garage conversion is cheaper than either because the structure exists. The lot usually decides: where there is room for a detached unit, most homeowners choose it.
Published 2026 guides put total city fees for a typical Los Angeles ADU at roughly $5,000 to $15,000: plan check, building permit, electrical, plumbing and mechanical permits, plus school fees above about 500 square feet and sewer connection fees where they apply. Units of 750 square feet or less are exempt from local impact fees under state law.
Yes, on the ADU only. The County Assessor adds the new unit as new construction at its market value and the main house keeps its existing assessed value; the whole property is not reassessed. A rough planning figure is a little over 1% of the ADU's assessed value per year, which rental income usually covers.
The City's LADBS Standard Plan Program pre-approves designs owned by private designers who charge for them; they shorten plan check, not the design bill. Los Angeles County's program offers pre-approved plans for unincorporated areas at low or no cost. Either way the plans still need a site-specific permit and site work, so the savings are in weeks of review, not tens of thousands of dollars.
Published 2026 guides put two-car garage conversions in Los Angeles at roughly $120,000 to $225,000, or $250 to $450 per square foot, depending on the slab, the required upgrades, plumbing under the slab, the electrical panel and the finish level. A two-car garage gives you a one- or two-bedroom layout; a one-car garage gives a studio.
Besides the cost, the honest one is that it changes how the backyard and the driveway are used and adds a second set of utilities, maintenance and, if you rent it, a landlord's responsibilities. We design around the backyard and say so to homeowners on the fence rather than selling a unit they do not need.
No. We price each ADU from the lot, the unit type and the plan set, and give a written line-item estimate after the complimentary site visit, then a fixed-price contract with change orders in writing. The benchmarks on this page come from published third-party sources and are meant to size the decision, not to replace an estimate.
Thinking about an ADU in Los Angeles? Call (323) 729-3140 or Schedule your complimentary site visit through our contact page. We will check the lot, the garage and the utilities and give you a written estimate before you spend anything on design.
AXE CONSTRUCTION INC · CSLB Lic #1069232 · Class B General Building 8383 Wilshire Blvd, Suite 363, Beverly Hills, CA 90211 · (323) 729-3140