This Accessory Dwelling Unit webpage is a one-stop-shop for information and resources to assist homeowners interested in creating an accessory dwelling unit or junior accessory dwelling unit on their property.

An Accessory Dwelling Unit, also known as an “ADU”, is a residential unit that provides independent living facilities including a kitchen, sleeping, and bathroom facilities.

A Junior Accessory Dwelling Unit, also known as a “JADU”, is a residential unit that is no more than 500 square feet in size, contained entirely within the walls of an existing residence and has a separate entrance, an efficiency kitchen and may include a separate bathroom or may share a bathroom within an existing residence.

ADUs may be either detached, attached, or created through the conversion of existing space into an ADU, as shown below.

Typically, the process will consist of the following steps. Please note, this is a typical process and not indicative of all ADU projects.

1. Contact a Professional: Staff recommends reaching out to a design professional with experience working on ADUs to develop a proposal that is tailored to you, as well as assisting you with understanding and obtaining permits.
2. Research: Before putting pen to paper, review the City’s ADU development standards in Chapter 22.43, which details development standards for ADUs/JADUs, additional technical studies that may be required, and other general requirements. Consider potential environmental constraints, such as FEMA flood zones, fire severity zones, and Wildland Urban Interface which could result in stricter building code and material standards. 
3. Preliminary Review: Once you have a good understanding of the scope of work you’d like to pursue, prior to submitting an application, work with a professional to draft preliminary plans. Email Us the draft plans and a Planner will provide you with preliminary feedback.
4. Submit Application: Review the ADU/JADU Building Permit Submittal Requirements and submit a Building Permit Application and pay all applicable permit filing fees. Staff strongly encourages you to review the  submittal requirements Section 22.43.150 and provide all the required information. 
5. Application Approval: Once approved, you will receive your building permit and you may begin construction. Please note, you will also likely be required to obtain approval and pay applicable fees to service providers, such as Central Contra Costa Sanitary District, Mountain View Sanitary District, Contra Costa Health for septic systems, and/or Contra Costa County Fire Protection District.
6. Construction: Find reputable contractors to assist with construction. Consider visiting the Contractors State License Board website for advice on hiring a contractor. If the property owner is acting as the general contractor, then identify a licensed plumber, mechanical, electrical subcontractor.
7. Inspections: Contact the Building Division at (925) 372-3596 to schedule inspections prior to occupancy.
8. ADU Ready for Occupancy: Once final inspections are complete, then you may move in and enjoy your ADU!

Each property owner’s needs will be different based on budget, the intent and purpose of their ADU, and physical constraints of the land. Costs associated with creation of an ADU or JADU are typically divided into hard and soft costs:

• Hard costs include construction costs; installation of utilities; design and engineering fees; and legal, permitting, and development impact fees.
• Soft costs may include financing costs; insurance; property tax; and maintenance and upkeep costs.

Most fees are tied to the valuation and scope of your project. The most notable fees include Building Permit fees and Engineering Development Impact fees. Staff recommends you review the City’s Fee Schedule (Building Division fees are on pages 2 through 7 and Engineering Division fees are on pages 13 through 15) and consult with the Building and Engineering Divisions to get a better understanding of the overall expected cost to acquire a Building Permit.

PLEASE NOTE: Per State law, effective January 1, 2020, through January 1, 2025, ADUs less than 750 square feet are not subject to impact fees and ADUs 750 square feet or larger are subject to impact fees proportional to the primary dwelling unit. School impact fees may still apply: Mt. Diablo Unified School District imposes impact fees for ADUs over 750 square feet and Martinez Unified School District imposes impacts fees for ADUs over 500 square feet. Furthermore, some prefabricated ADUs may not be subject to Title 24 Energy Calculation fees.

The California Housing Finance Agency (CalHFA) ADU Grant Program occasionally provides financial assistance for predevelopment costs necessary to build and occupy an ADU or JADU. For additional information, please see CALHFA’s ADU Grant Program at https://www.calhfa.ca.gov/adu/.

The City’s ADU regulations were amended in accordance with State law and became effective August 19, 2023.

Notable development standards include:

Frequently Asked Questions

Additional Resources

• Martinez ADU/JADU Code
• Martinez User Fee Schedule
• California ADU Website
• HCD ADU Handbook
• AARP: The ABC’s of ADUs
• Central Contra Costa Sanitary District
• Martinez ADU Brochure

If you have any questions about building an ADU or JADU, please contact:

Planning Division
(925) 372-3515
Email Us

Building Division
(925) 372-3515
Email Us