How big can an ADU be in Modesto?

Detached ADUs in Modesto can be up to 1,200 sq ft. Attached ADUs: 50% of primary home, max 1,200 sq ft. JADUs up to 500 sq ft.

How much does it cost to build an ADU in Modesto?

Build costs typically range $90,000 – $195,000, or $145 – $210 per square foot.

Verified March 14, 2026

ADU Regulations in Modesto, California

Q: What are the setback requirements for ADUs in Modesto?

Front: Same as primary dwelling. Side: 4 ft. Rear: 4 ft.

Stanislaus County · CA · Pop. 220,000

Max ADU Size

1,200

sq ft detached

Rear Setback

4 ft

Permit Timeline

60 days

Build Cost

$90,000 – $195,000

Zoning

Allowed ADU Types

✓Detached ADU

✓Attached ADU

✓JADU (Junior ADU)

✓Garage Conversion

Max per lot: 2 ADUs✓ No owner-occupancy required

Modesto follows California state ADU law; by-right approval

Source: City of Modesto — Accessory Dwelling Units · Modesto Municipal Code Section 10-1.8.10

Dimensions

Size & Setback Requirements

Detached

1,200

sq ft max

JADU

500

sq ft max

Attached

50% of primary home, max 1,200 sq ft

Setbacks

front

Same as primary dwelling

side

4 ft

rear

4 ft

Max height: 16 ft

Lot coverage: Per underlying zone

Modesto's established neighborhoods often have alley access ideal for rear ADUs

Permitting

Permit Process

Department

Modesto Community & Economic Development

Review Timeline

60 days

Permit Fees

$3,500 – $8,500

Impact Fees

Impact fees waived under 750 sq ft

Required Documents

›Site plan
›Floor plans
›Elevations
›Title 24 energy compliance
›Structural drawings

Modesto's online permit portal accepts ADU applications

Visit Modesto Community & Economic Development →

Infrastructure

Utilities & Requirements

Solar

Required

Parking

Not required

Separate Meter

Optional

Fire Sprinklers

See note

Sewer: Connect to City of Modesto sewer system

Fire Sprinklers: Not required unless primary structure requires them

Parking: No additional parking required

Financials

ADU Costs in Modesto

Typical Build Cost

$90,000 – $195,000

Cost per Sq Ft

$145 – $210

Monthly Rental

$950 – $1,650/mo

Property Value Added

Adds $80,000 – $155,000 to property value

Available Grants & Programs

★CalHFA ADU Grant Program available

Central Valley pricing makes Modesto one of the more affordable markets for ADU construction

Use the free ADU Cost Calculator →

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Disclaimer: Information is compiled from publicly available municipal codes for general informational purposes only. It does not constitute legal, zoning, or construction advice. Regulations change frequently. Always verify with your local planning department. Last verified: March 14, 2026. Verify with Modesto Community & Economic Development

Modesto Quick Facts

Max size1,200 sq ft
Rear setback4 ft
Permit timeline60 days
Build cost$90,000 – $195,000
Rental income$950 – $1,650/mo
Owner occupancyNot required

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Official Source

City of Modesto — Accessory Dwelling Units

Modesto Municipal Code Section 10-1.8.10

Last verified: March 14, 2026

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ADU rules change often.

Get notified when Modesto's regulations update, plus guides on permitting and financing.