What Are ADU Permit Fees?

Key takeaways

• Permit fees are not one bill. They are five or more charges from different offices.
• In California, an ADU of 750 square feet of interior living space or less pays no impact fees ¹.
• Small ADUs still pay plan review, permit and inspection fees. The size rule does not touch those.
• Above 750 square feet, impact fees may apply, scaled to the size of your main home ¹.
• On Sacramento’s own 2026 sheet, one extra square foot roughly doubles the total ².
• School and utility charges follow their own rules. Ask those offices directly.

What ADU permit fees mean, in plain English

Before you build, the city has to check your plans. Then an inspector visits during the work. Permit fees pay for that staff time.

Many places also charge impact fees. An impact fee is money for public things a new home is said to use, like parks, roads or flood control. It is not for checking your plans.

Other offices may charge you too. The school district may collect a school fee. The water and sewer provider may charge to hook up the new unit.

So “permit fees” is a family of charges. Some come from the city. Some come from other agencies that serve your lot.

Why permit fees matter to you

Fees are cash you pay before a single wall goes up. Most loans and bids do not cover them unless you ask.

They can also shape the design. In California the 750 square foot line can switch impact fees on or off. A small change in size can move your bill by thousands of dollars on some city sheets.

Fees are part of your soft costs, the costs that are not labor or materials. Leave them out and your budget will be short.

How ADU permit fees work, step by step

The order varies by city. This is the common pattern.

1. You submit plans. The city often charges a plan review (plan check) fee at this point.
2. Staff check the plans. They compare them with the building code and zoning. Extra review rounds may cost more in some cities.
3. The city prices the permit. Many cities use a valuation: square feet times a city rate. Fees are then a share of that number.
4. Other agencies add their charges. The school district, sewer and water providers and special districts each bill on their own.
5. You pay and the permit is issued. Most remaining city fees, including any impact fees, are due here.
6. Inspections follow. These are usually covered by the permit fee. A failed inspection may bring a re-inspection fee in some cities.

Your city may add steps of its own, such as a separate planning review.

The five kinds of fee on an ADU permit

California’s rule: the 750 square foot line

Fee rules vary by state; outside California, check the state and local law (our ADU laws by state table tracks them).

In California, the rule sits in Government Code § 66311.5, which took that number on 1 January 2026 when SB 543 (Stats. 2025, ch. 520) renumbered former § 66324. Before 25 March 2024 the same rule was in § 65852.2.

Subdivision (c)(1) says a local agency, special district or water corporation “shall not impose any impact fee” on an ADU with 750 square feet of interior livable space or less, or a junior ADU with 500 square feet or less.

An ADU larger than 750 square feet can be charged impact fees, but only “proportionately in relation to the square footage of the primary dwelling unit.”

The exemption covers impact fees only. Subdivision (c)(2) defines an impact fee by reference to Gov. Code § 66000(b), adds park fees under § 66477, and excludes connection fees and capacity charges.

Section 66000(b) itself leaves out “fees for processing applications” ³, so plan review, permit and inspection fees fall outside the exemption and a small ADU still pays them.

Utility charges follow their own rule. An ADU is not a “new residential use” for connection fees unless it is built with a new single-family home (§ 66311.5(b)).

For an ADU inside an existing house or accessory structure under § 66323(a)(1), the utility may not require a separate connection or charge for one (subdivision (d)).

For other ADUs it may require a new connection, with a fee proportionate to the unit’s burden by square feet or drainage fixture units (subdivision (e)). See utility connection requirements.

Sources: [1]

School fees and utility hookups, in plain words

California school districts can charge a fee on new homes under Education Code § 17620 ⁵. For other residential work, that section allows the fee only when the added assessable space is more than 500 square feet.

State ADU law plugs into that line. It treats an ADU or junior ADU under 500 square feet of interior livable space as work that does not add 500 square feet ¹. So a very small unit is often outside the school fee. Ask the district how it applies this to your plans.

Water and sewer work differently again. For a conversion inside your existing house or an existing accessory building, the provider may not require a separate hookup or charge you for one. For a new detached unit, it may require one, with a charge scaled to the unit’s size or plumbing load ¹.

Sources: [5] [1]

Rules outside California

California is unusual. It has a state law that bans impact fees on small ADUs. Most states leave fees to cities and counties.

Outside California, expect your local fee schedule to apply in full unless your state says otherwise. Some states have passed their own ADU laws in recent years. Check the state-by-state ADU law table, then your city’s fee page.

The same five fee types show up almost everywhere. The names, the amounts and the order you pay them change.

One city’s fee sheet: Sacramento, 749 vs 750 vs 1,200 sq ft

The City of Sacramento publishes an ADU fee estimate for new construction (form CDD-0419, revised 12 July 2026) with three columns. These are the city’s own figures for its own fees, not a California average ².

One extra square foot roughly doubles the bill on this sheet, because the three impact fees switch on.

The sheet excludes school fees (paid at the district), sewer and regional sanitation fees, and special district fees.

Note that the statute measures interior livable space, while the worksheet labels its column by square footage; if your plans show exactly 750 square feet of interior livable space, ask the city how it measures before paying an impact fee.

Building-permit and plan-review subtotals are HyreADU’s addition of the sheet’s two lines.

How “proportionate” works above 750 sq ft

A hypothetical, for arithmetic only. Suppose a city’s park impact fee is a hypothetical $10,000 for a new single-family home, and you build a 1,000 sq ft ADU behind a 2,000 sq ft house. The formula shows one common way cities apply the rule.

The statute ties the charge to the main home’s square footage but does not print a formula. The ratio above is one way cities apply it; your city’s fee resolution decides. Sacramento’s 1,200 sq ft column, for example, uses its own schedule.

Where you will see these fees

• The city fee schedule. In California, a city, county or special district with a website must post its current fee schedule there ⁴.
• A fee estimate worksheet. Some cities, like Sacramento, publish one for ADUs ².
• The plan check invoice when you submit drawings.
• The permit invoice when the permit is ready to issue.
• A school district receipt. The city may ask for it before it issues the permit.
• A utility letter or invoice for any new water or sewer connection.
• Your contractor’s bid, often as an allowance or an exclusion. Read that line closely.

What drives the size of your fee bill

No two cities price the same way. These are the things that move the total.

• Interior livable space. In California, 750 square feet is the impact-fee switch ¹.
• The project valuation. Cities that price permits by valuation charge more as square feet rise. See why permit valuations are not build prices.
• The ADU type. A conversion inside an existing building is treated more gently on utility hookups than a new detached unit ¹.
• The size of your main home, because fees above 750 square feet must be proportionate to it ¹.
• Which districts serve the lot. Flood, fire, sewer and transit districts each may add a line, as on Sacramento’s sheet ².
• Review rounds. Incomplete plans can mean more review time, which some cities bill.

Staying at 750 square feet or less: benefits and limits

Permit fees compared with related costs

Common misreadings

Myth A small ADU in California pays no fees.

Reality It pays no impact fees. Plan review, permit and inspection fees still apply, and Sacramento’s 749 sq ft column still totals about $5,272 ².

Myth Fees above 750 sq ft are the full new-home rate.

Reality They must be proportionate to the main home’s square footage (§ 66311.5(c)(1)).

Myth The rule is in Gov. Code 65852.2.

Reality That section was repealed in 2024. The current section is § 66311.5; a city document citing 65852.2 or 66324 is out of date.

What to ask the city and your builder

• Does your city publish an ADU fee estimate sheet? Which version is current?
• How do you measure interior livable space for the 750 square foot rule?
• Which fees are due at plan check, and which at permit issue?
• Which outside agencies will bill me: school, sewer, water, fire, flood?
• Is my unit a conversion or new construction for utility hookup rules?
• Is there a fee for extra plan review rounds or re-inspections?
• Builder: are permit and agency fees in your bid, an allowance, or excluded?

How to find your own fee total

1. Find your city’s ADU fee estimate or fee schedule; many building departments publish one. Our California ADU fees by city study links the ones we have read.
2. Measure the interior livable space on your plans and note which side of 750 sq ft it falls on.
3. Call the school district for its residential rate; it is collected separately.
4. Ask the water and sewer providers whether your ADU type needs a new connection under § 66311.5(d) or (e).
5. Add the totals to the soft-cost side of your budget, then run the ADU fee estimator.

Checklist: fees before you sign a contract

1. Download the current fee schedule and any ADU fee worksheet.
2. Write down the interior livable square footage from your plans.
3. Mark each fee line as city, school, utility or district.
4. Get the school district’s answer in writing if your unit is near 500 square feet.
5. Ask the sewer and water providers for their connection rule in writing.
6. Put all fees in your budget as a separate soft-cost line.
7. Recheck the totals before you pay, as schedules can change.

Where permit fees sit in the project

1. ADU size (interior livable space)
2. impact-fee exemption or proportional fee
3. permit fee total
4. soft costs
5. cost estimate

Related guides, tools and research

• Fee estimator toolSee which fee lines apply to your size
• ADU fee statisticsFee figures with their sources
• Fee sheets city by cityCity fee sheets we have read
• ADU permit valuationsWhy the valuation on a fee sheet is not a build price
• How the ADU permit process worksThe full permit path
• ADU cost guideWhere fees sit in the total

Related terms

ADU Soft Costs

ADU soft costs are the parts of an accessory dwelling unit budget that pay for paperwork, professional services and money rather than for physical construction: design, engineering, surveys, permits and government fees, utility charges, insurance and financing costs.

ADU Cost Estimate

An ADU cost estimate is a written, itemized prediction of what it will cost to build a specific accessory dwelling unit on a specific lot, listing the work, materials, allowances, exclusions and assumptions behind the total.

ADU Hard Costs

ADU hard costs are the money spent physically building an accessory dwelling unit: site preparation, foundation, framing, roofing, windows, mechanical, electrical and plumbing systems, finishes, and the trenching that brings utilities to the unit, together with the contractor’s labor, overhead and profit.

ADU Utility Connection

An ADU utility connection is the way an accessory dwelling unit gets water, sewer, electricity and, where used, gas: either as a branch off the main house's existing service, or as a new, separate connection running directly from the utility to the unit.

ADU Permit

An ADU permit is the building permit a city or county issues to allow construction of an accessory dwelling unit, after checking the plans against local zoning standards and the building code.

ADU Cost Per Square Foot

ADU cost per square foot is the cost of an accessory dwelling unit divided by its floor area, a shorthand for comparing units of different sizes.

ADU Construction Process

The sequence of building an ADU: feasibility, design, permits, site work, foundation, framing, rough-in inspections, finishes and final inspection.

Also referenced from: ADU Size, ADU Bathroom, ADU Cost Per Square Foot, ADU Cost Estimate, ADU Soft Costs, ADU Permit, Building Department, Permit Expediting, ADU Utility Connection, ADU Water Connection, ADU Sewer Lateral, ADU Design-Build, ADU Grant