How Much Do Adu Permits Cost? | Fee Ranges By City

People often ask, how much do adu permits cost? and the number can swing a lot. One town bills mostly by valuation. Another bills by hourly review. Some waive certain fees under a size cap. Others don’t. This article breaks the bill into plain line items, shows planning ranges that match common projects, and gives you a fast method to get a near-exact total for your lot for most projects.

What adu permit fees usually include

Most invoices bundle several departments. The names change, yet the parts tend to repeat. Think of it as three layers: review, permission to build, and fees tied to added demand on city systems.

Fee category	What it pays for	Typical range
Building permit	Permit issuance plus required inspections for code compliance	$1,500–$8,000+
Plan review	Staff review of drawings, corrections, and rechecks	$800–$6,000+
Zoning or planning review	Checks setbacks, height, lot limits, parking, and ADU rules	$0–$2,500
Trade permits	Electrical, plumbing, mechanical permits if not bundled	$0–$2,500+
Grading or right-of-way	Work that touches the street, sidewalk, or public easement	$0–$4,000+
Utility connection or capacity	New meter, upsized line, or connection charge where required	$0–$15,000+
Impact or development fees	Fees tied to parks, roads, or similar public systems	$0–$20,000+
School district fees	District impact fees in places that charge per added floor area	$0–$6,000+

Adu permit cost factors by city

Fee totals change because cities bill in different ways, and because certain project details trigger add-ons.

Local billing method

Some places set a fee from construction valuation. Others mix valuation with hourly review. If your city uses hourly review, extra correction cycles can raise the bill. If your city uses valuation, bigger scope and higher finishes can raise the valuation that drives fees.

Size thresholds

Fee rules often change at size cutoffs. In parts of California, many cities follow a 750-square-foot cutoff for development impact fees, with proportional charging over that size. San José also notes size cutoffs for certain local impact fees and school fees on its ADU FAQ page.

Detached versus attached

Detached ADUs more often need new trenching, a new service panel, and separate sewer or water work. Attached builds and conversions can reuse more of what’s there, so fees tied to utilities may stay lower.

Site triggers

Right-of-way work, steep lots, protected trees, flood zones, coastal overlays, and historic review can add review steps and separate permits. One sidewalk cut can add traffic control fees that don’t show up in early ballparks.

How Much Do Adu Permits Cost?

Use these ranges for early budgeting. Then use the next section to pull a line-item estimate that matches your plan.

Conversions and garage ADUs

Conversions often sit on the low end since you’re not building a new foundation and you may reuse existing utility lines. A common planning range is $2,000 to $6,000 in permit and review fees, then add any utility upgrades your inspector requires.

Detached ADU under 750 square feet

Small detached units can still trigger utility work, yet fee caps and waivers can keep impact-style fees low in some places. Many owners land in a $4,000 to $12,000 planning range, then add the cost of any new meter, panel upgrade, or sewer capacity charge.

Detached ADU over 750 square feet

Crossing a size threshold can bring in impact fees and higher review effort. It’s common to see $10,000 to $25,000+ in permit and related agency charges in higher-fee cities, before major utility connection work.

Two-story ADU or complex site

Stairs, long spans, tall walls, and retaining work can add engineering review and extra inspections. Right-of-way permits and stormwater requirements can also stack on. Budget on the upper end unless your city confirms the add-ons don’t apply.

Fast way to get your near-exact total

You can get a fee estimate in one afternoon. The trick is to collect the inputs that drive billing, then ask the permit desk for the same “fee worksheet” staff use.

Step 1: Pull current fee pages for your jurisdiction

Start with your city or county construction permit fee page, plus any ADU handout. Some places also publish online estimators. Seattle explains how plan review and permit fees are calculated and when payments are due on Seattle SDCI’s permit cost page.

Step 2: Write down four facts that change fees

• ADU type: conversion, attached new build, detached new build
• Gross floor area in square feet
• Utility plan: reuse existing laterals or add new service
• Street work: any taps, trenching, or work in the public easement

Step 3: Ask for a line-item estimate

Ask the permit desk for the fee list that would appear on your permit invoice at issuance. Ask them to break out building permit, plan review, zoning, trade permits, right-of-way, and any impact-style charges. This list is the backbone of your budget.

Step 4: Check fee caps or waivers tied to ADU size

Many places have rules that change charges under certain sizes. San José notes that school impact fees do not apply to ADUs under 750 square feet and that park impact fees also do not apply under that cutoff. Those details are on San José’s ADU FAQ page. If you’re outside San José, look for a similar FAQ or fee bulletin in your city.

Step 5: Add a buffer that fits your billing style

If your city bills hourly for review, budget extra for one more correction cycle. If your city bills from valuation, budget for scope changes that raise valuation, like an added bathroom or higher-end finishes. Also keep room for utility surprises once a contractor opens a trench.

Common fee surprises and how to spot them early

Most sticker shock comes from a list of repeat surprises. Catching them early can save you a lot of stress.

Right-of-way permits tied to utility work

If you need a new water tap, a sewer lateral tie-in, or a sidewalk cut, your city may require traffic control, street restoration, and separate inspection trips. Ask your contractor where each trench will run. If any segment crosses into public space, price the right-of-way permit early.

Capacity charges tied to fixture count

Some utilities charge based on added fixtures or added dwelling units. This can dwarf your city permit fees. Call the water and sewer provider and ask what triggers a capacity charge for an ADU on your parcel.

Impact fees that depend on final square footage

Impact fees are sometimes calculated after zoning review confirms final floor area. If your plan is near a cutoff, decide early whether you’re staying under it. Don’t wait until plan review to trim a few square feet.

Separate fire review

Some jurisdictions route ADU plans through a fire agency for access, sprinklers, or hydrant spacing. Ask if fire review is automatic for detached units, especially on long driveways.

Keeping permit costs from creeping up

You can’t skip core fees, yet you can keep the scope tidy so you pay for what you need and avoid extra permits that come from design choices.

Lock the size before you submit

Each size change can trigger recalculation, rechecks, and new fee totals. If you’re aiming for a size cutoff, keep a simple “do not cross” number in your plan set and stick to it.

Reduce street work when feasible

Routing utilities through your own yard can reduce street permitting in some cases. Ask a licensed contractor for two routing options and compare the fee impact.

Use standard construction details

Simple spans, standard shear walls, and a straightforward roofline can reduce engineering time and reduce review back-and-forth. That helps in hourly review cities, and it can keep valuation lower in valuation-based cities.

Bundle trade work when it avoids repeat inspections

If you’re already doing a panel upgrade or a service change, ask whether bundling it with the ADU permit avoids duplicate inspection trips. Separate permits can mean separate review and inspection fees.

Budget worksheet you can paste into your notes

Once the city gives you line items, fill in this worksheet. It keeps your estimate clear and makes it easy to ask follow-ups.

Line item	Question to ask	Your number
Building permit	Does it include all inspections, or do some inspections bill by the hour?	$____
Plan review	Flat fee or hourly billing? Any charge for resubmittals?	$____
Zoning or planning review	Separate ADU zoning check, design review, or overlay review?	$____
Trade permits	Are electrical, plumbing, and mechanical bundled or separate?	$____
Right-of-way	Any public easement work, traffic control, or street restoration?	$____
Utility charges	New meter, panel upgrade, upsized line, or capacity charge?	$____
Impact fees	Any waiver under a size cap? If charged, is it proportional?	$____
School fees	Does your district charge at your ADU size?	$____
Other agency	Fire review, stormwater review, tree review, or similar?	$____
Buffer	One extra review cycle plus a small utility surprise	$____

Final checks before you pick a number

Permit fees are only one slice of total ADU cost, yet they can swing by five figures once utilities and impact fees show up. Get the line-item list early, pick a size that matches your city’s thresholds, and keep street work as simple as your site allows.

If you’re still wondering how much do adu permits cost? for your place, take your sketch, your square footage, and your utility plan to the permit desk and ask for the invoice-style breakdown. You’ll walk away with a budget you can trust.