The cost of a Los Angeles ADU permit typically falls between about $1,000 for a small garage conversion and more than $8,000 for a newly built detached unit. The Los Angeles Department of Building and Safety (LADBS) calculates most charges from your project’s construction valuation, and California law eliminates several impact fees for units under 750 square feet. What you pay depends almost entirely on how big the unit is, how it’s built, and which agencies get a share.
How LADBS Calculates the Building Permit Fee
The building permit fee is the largest single charge on most ADU projects. It scales with the total valuation of your project, meaning estimated labor and materials combined. LADBS uses the fee table in LAMC Section 91.113:
- Up to $2,000 valuation: $65 flat fee
- $2,001–$20,000: $40 plus $1.25 per $100 of valuation
- $20,001–$50,000: $170 plus $6.00 per $1,000 of valuation
- $50,001–$100,000: $195 plus $5.50 per $1,000 of valuation
- $100,001–$500,000: $395 plus $3.50 per $1,000 of valuation
- $500,001–$1,000,000: $520 plus $3.25 per $1,000 of valuation
On top of the base permit fee, LADBS adds a plan check fee equal to 90% of the building permit fee, which covers the engineers who review your blueprints for structural and code compliance.1City of Los Angeles. Appendix 2.4 – Summary of Case Filing and Building Permitting Fees A $500 building permit fee brings roughly another $450 in plan check. Together, these two charges form the backbone of what you’ll pay LADBS directly.
You’ll also pull separate sub-permits for electrical, plumbing, and mechanical work. Each has its own fee based on the number of fixtures or the complexity of the installation. A garage conversion with minimal new plumbing costs far less in sub-permits than a ground-up build with a full kitchen and bathroom.
What the Totals Look Like for Real Projects
The city publishes sample estimates. A new one-story, 1,200-square-foot ADU with a construction valuation of $121,200 carries a total permit fee of approximately $8,448. A 400-square-foot garage conversion valued at $20,000 comes in around $1,045.1City of Los Angeles. Appendix 2.4 – Summary of Case Filing and Building Permitting Fees The gap is enormous, and it’s driven almost entirely by valuation.
That valuation figure matters more than most homeowners realize. It must reflect realistic current market rates for materials and labor. Lowballing it to shave fees invites corrections and delays during plan check. LADBS runs an online fee calculator where you can input occupancy category, construction type, and floor area to generate a preliminary estimate before submitting anything.2Los Angeles Department of Building and Safety. Plan Check Fee Estimate System The tool warns that final fees are set at submission and may differ, but it will get you in the right ballpark for budgeting.
Impact Fee Waivers Under State Law
Smaller ADU projects catch a major break here. California Government Code Section 65852.2 prohibits any local agency, special district, or water corporation from imposing impact fees on an ADU of less than 750 square feet.3California Legislative Information. California Government Code 65852.2 For units of 750 square feet or more, impact fees must be proportional to the ADU’s size relative to the primary home rather than charged at the full rate for a new residence.
The same statute blocks cities from requiring a separate utility connection for certain ADUs, which wipes out the connection fees and capacity charges that would otherwise apply. If your ADU is built within or attached to the existing home, or converts existing space such as a garage, the city cannot force a separate water or sewer hookup unless the ADU was built alongside a brand-new primary dwelling.3California Legislative Information. California Government Code 65852.2 For detached ADUs that do require new connections, the fees must be proportional to the unit’s actual burden on the system.
These waivers can save thousands on a smaller project. One important carve-out: the 750-square-foot prohibition applies to local agencies and special districts, not to school districts.
School District Fees
School districts have independent authority under Education Code Section 17620 to charge developer fees on new residential construction to fund school facilities.4California Legislative Information. Education Code 17620 For residential additions and conversions, these fees kick in when the increase in assessable space exceeds 500 square feet. A 480-square-foot garage conversion falls below the threshold; a 600-square-foot new build does not.
The split between the 500-square-foot school threshold and the 750-square-foot impact fee waiver trips up a lot of homeowners. They hear “under 750 square feet, no impact fees” and assume that covers everything. It doesn’t. School districts were deliberately excluded from the state’s ADU impact fee waiver, and LAUSD sets its own fee schedule that it adjusts periodically, so check the district’s current per-square-foot charge when budgeting for a unit above 500 square feet.
Sewer, Fire, and Other Agency Charges
The Los Angeles Bureau of Sanitation charges a Sewerage Facilities Charge when a project adds a new dwelling unit to a lot. The charge is based on estimated sewage flow rates set by the Board of Public Works, not a flat fee.5Los Angeles Municipal Code. Los Angeles Municipal Code SEC 64.11.3 – Basis for Sewerage Facilities Charge The calculation accounts for the type of unit and gives credit for any existing structures that previously contributed to sewer usage on the lot.6Los Angeles Municipal Code. Los Angeles Municipal Code SEC 64.16.1 – Sewerage Facilities Charge for Sewer Converting a garage that never had plumbing produces a larger charge than modifying a space that already had a bathroom.
Properties in a Very High Fire Hazard Severity Zone face additional fire department review. Requirements include minimum fire-flow capacity from nearby hydrants, limits on distance from a paved access road at least 20 feet wide, and maximum distances to a public hydrant. A detached ADU with an approved fire sprinkler system can sit up to 300 feet from vehicular access; without sprinklers, the limit is 150 feet. These rules don’t always add permit fees, but they can force design changes that drive up construction costs, and a fire department plan check in a hazard zone has its own processing step.
Cutting Costs With the Standard Plan Program
One of the most effective ways to trim both cost and timeline is the LADBS ADU Standard Plan Program. Licensed architects and engineers design ADU plans that LADBS pre-approves for compliance with building, residential, and green building codes. When you select a pre-approved plan, LADBS reviews only site-specific factors like zoning and foundation requirements rather than checking the full set of blueprints from scratch.7Los Angeles Department of Building and Safety. ADU Standard Plan Program
The city owns at least one pre-approved plan that homeowners can use at no cost. Others are available for purchase directly from the design firms that created them. You give up some design flexibility, but for homeowners who don’t need a custom layout, the faster plan check and reduced architectural fees often more than offset the constraint. The program also lowers the chance of plan check corrections that trigger re-review fees.
Why 750 Square Feet Is the Magic Number
If you have flexibility on size, the financial case for staying under 750 square feet is hard to ignore. Below that threshold, state law wipes out impact fees from the city and special districts, eliminates the separate-utility-connection requirement for many project types, and forces any remaining fees to be proportional rather than flat-rate.3California Legislative Information. California Government Code 65852.2 Combined with the lower building permit fee that comes with a smaller valuation, a 700-square-foot unit can cost a fraction of what an 800-square-foot unit costs in permits alone. School fees still apply above 500 square feet regardless, but the overall savings from staying under 750 remain substantial on most projects.
If You Already Have an Unpermitted Unit
Homeowners with an existing unpermitted unit face a different cost picture. The City of Los Angeles has a formal legalization pathway under the Unpermitted Dwelling Unit Ordinance (Ordinance No. 184,907), which lets property owners bring qualifying units into compliance. The program carries a significant condition: you must provide at least one low- or moderate-income affordable housing unit for each unit you legalize, enforced through a recorded Affordable Housing Land Use Covenant on your property.8Los Angeles City Planning. Unpermitted Dwelling Units
The process runs through three city departments: City Planning, LADBS, and the Housing and Community Investment Department. You’ll file an inter-agency referral form and a public benefit application, then satisfy LADBS plan check requirements to prove the unit meets life safety standards. On top of the standard permit fees that apply to any ADU, expect the cost of bringing non-compliant construction up to code, which can dwarf the permit fees themselves depending on how the unit was originally built.