Building an additional living space on your property sounds like it should be simple. However, several crucial laws and restrictions apply to ADUs. Converting a basement into a starter apartment for a young adult or building a small rental flat for extra income requires thorough planning and diligent permit applications. Let’s discuss ADU permits and the costs you can expect in 2025.

What Is an ADU?

An accessory dwelling unit (ADU) is an additional housing space that is typically built after the main structure. ADUs are smaller than the primary dwelling and generally intended to house a person from the family, like a grandparent, an adult child, or a third unrelated party that pays rent to the property owner. 

Accessory dwelling units provide the necessary amenities for a resident to live independently of the primary dwelling. An ADU will always include provisions for living, sleeping, eating, cooking, and hygiene. There is no single ADU definition, as they come in many different forms. The main ADU types are:

  • Detached new constructions
  • Garage conversions
  • Above garage/workshop
  • Bump-outs
  • Basement conversions
  • Internal ADUs

Related post: The Benefits of Adding an Accessory Dwelling Unit (ADU) to Your Property

What Are the San Diego Permit Requirements for an ADU?

Whether you’re constructing a new ADU, converting an existing area, or placing a pre-fabricated ADU, there are key permit requirements to which you must adhere. First, you must apply for a building permit that covers site prep, foundations, and utilities. Next, you need an ADU-specific permit that covers legal occupancy and compliance with San Diego ADU regulations.

Before starting, you must also go through the plan review and approval process. You will send architectural plans, engineering reports, and any other required documentation to local authorities. You may need to make modifications to meet ADU standards before your plans are approved. Without securing all necessary permits, your ADU will be considered illegal. Some of the other fees you can expect to pay include:

  • Mapping
  • Lead hazard prevention
  • Sewer and water capacity
  • Stormwater inspections

How Much Do ADU Permits Cost in San Diego?

ADU permits can cost between $9,000 and $20,000, but the exact fee depends on the ADU type, the size of your project, and your location. Based on the specifications of your ADU, it may incur higher permit fees as it can have a more significant impact on the property, environment, and surrounding dwellings.

ADU Type

Detached and bump-out ADUs typically have higher permit fees than those that are included in the same footprint as the original structure. Conversion ADUs can have lower permit fees, but the exact cost varies significantly. The permit fees for ADUs built on top of the existing structure, like above garage apartments, change based on the new size and height of all structures on the property.

Project Size

The bigger the ADU, the higher the permit fees. The maximum floor space of a detached ADU is 1,200 square feet. Nonetheless, conversions of the existing structure aren’t subject to the same restrictions. Smaller units may not require fees like impact and school fees, which can increase the overall fee cost significantly.

Location

ADU permit fees vary between states, but within California, different zones apply in neighborhoods. For example, in coastal and historically significant areas, ADU permit fees can be higher. Depending on your zone, you may also be legally required to include an appropriate off-street parking space, which can affect your plans.

How the San Diego Housing Crisis Impacts ADU Regulations

California officials have been encouraging the development of ADUs to ease the state’s housing shortage and provide more affordable housing. A series of laws have been passed to make it easier to build ADUs. For example, there is a law – SB13 – which waives specific permit fees such as development impact, school, and park fees for ADUs under 750 square feet. The same law offers reduced permit fees for ADUs bigger than 750 square feet.

How Much Do ADUs Cost to Build in San Diego?

Starting with the design and planning fees, you can expect to pay between $8,00 and $15,000 for architectural plans. Engineering plans will cost an additional $2,500 to $5,000, plus Title 24 energy calculations, which can cost up to $1,000. Then, you must include your permit fees, which can cost up to $20,000, as mentioned.

Construction expenses vary drastically according to the size of the ADU, the materials, and the complexity of the build. Economy ADUs start at $130,000 minimum for one bedroom and one bathroom. Choosing high-end materials and including multiple rooms can increase the construction costs to more than $200,000 for 600 square feet.

How to Ensure Compliance With Permit Regulations

The number of laws and fees involved in ADU construction can be overwhelming, particularly for those who have never been involved in the dwelling construction process before. It is crucial to work with a qualified general contractor with experience in permit law to ensure full compliance. At Jeff Seals Remodeling, we handle every aspect of a construction or conversion project, from planning to building, including permit applications and compliance.

You can apply for your own permits, but with so many moving parts and laws that are consistently being updated and changed, it’s easy to miss one aspect that can derail your entire project. Whether attaching a backyard cottage for a grandparent or building an above-garage apartment for your adult child, the Jeff Seals Remodeling team can manage all the details.

Building the Perfect ADU

Planning, designing, and applying for the relevant permits are the most critical aspects of building an ADU. Working with an expert team helps you navigate the complexities and hurdles commonly associated with creating an accessory dwelling unit in San Diego. Contact Jeff Seals Remodeling to discuss your ADU plans and develop a strategy to ensure compliance throughout the building process.