What is an ADU? Understanding Accessory Dwelling Units

In the evolving landscape of residential housing, Accessory Dwelling Units (ADUs) are increasingly becoming a topic of discussion. Serving as versatile spaces that cater to various needs, they offer homeowners a unique blend of financial, housing, and aesthetic advantages.

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Our comprehensive FAQ list aims to provide valuable insights into ADUs, enabling you to explore all their benefits and considerations easily.

Christian Johnston

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1. What is an Accessory Dwelling Unit?

An ADU, short for Accessory Dwelling Unit, is a secondary housing entity residing on the same lot as the primary residence. Depending on its design, this space can be attached to the main dwelling, be an entirely detached structure, or even emerge from an adapted part of an existing structure such as a garage. ADU’s are often referred to as a "secondary housing unit", "backyard cottage", or "auxiliary dwelling unit".

2. What are the benefits of having an ADU?

The shortage of affordable housing is a growing concern in many areas, and there is increasing interest in alternative solutions to address this issue. One such solution that has gained traction is the use of accessory dwelling units. According to a report by the California Department of Housing and Community Development, homeowners, cities, and counties are showing interest in ADUs as a potential solution to the affordable housing shortage.

• Rental Income

Adding an Accessory Dwelling Unit (ADU) to a home can provide homeowners with a range of benefits. For one, it allows them to generate rental income, which can be used to offset mortgage payments or other financial obligations. This can be a smart financial move for homeowners looking to maximize their earning potential and get the most out of their property.

• Housing for your family

Another key benefit of these versatile spaces is that they offer flexibility for homeowners with changing needs over time. For example, an ADU can be used to accommodate elderly parents who need extra care or returning adult children who need a place to stay while they get back on their feet. 

In areas with high housing demand, properties with ADUs may also see an increase in market value, making them a wise investment for homeowners looking to maximize their return on investment.

3. How is an ADU different from a guest house or in-law suite?

Though all three – ADUs, guest houses, and in-law suites – serve as supplementary living spaces, they harbor distinct differences. An ADU boasts of complete independence, featuring its own kitchen and bathroom, and holds the potential for rental. Meanwhile, guest houses or in-law suites, sometimes referred to as "alternate" or "attached dwelling units", are typically geared for transient stays or close family and might not be as equipped as a full-fledged residential unit.

4. What are the common regulations for building an ADU?

Constructing an ADU demands strict adherence to local zoning ordinances and building regulations. Commonly imposed rules dictate constraints on size, height, positioning, and sometimes aesthetic conformity to ensure the structure integrates seamlessly with the surrounding environment. Moreover, the provision of utilities, such as water, electricity, and sewage, must align with prevailing standards. A consultation with local authorities or professionals knowledgeable in "accessory dwelling unit regulations" is strongly advised before commencing any ADU project.

5. What are the different types of ADUs?

ADUs can manifest in various forms, each tailored to the specific needs of homeowners and the innate dynamics of the property.

Illustration depicting various types of accessory dwelling units.
Illustration depicting various types of accessory dwelling units.

The choice of ADU essentially pivots on individual needs, property specifics, and local regulatory stipulations.


JADUs are diminutive units within the primary residence and are often equipped with a basic kitchenette.

• Detached ADUs

Detached ADUs stand solitary on the premises, providing spacious areas and comprehensive amenities.

• Attached ADUs

Attached ADUs merge with the primary residence, offering a middle ground between closeness and independence.

• Garage Conversions

Garage conversions utilize existing infrastructure to transmute into functional ADUs, ensuring cost-effectiveness.

6. How much does it cost to build an ADU?

While freestanding ADUs tend to be more costly than their attached counterparts or internal transformations, a general ballpark figure spans between $150,000 to $350,000.

To effectively budget for an ADU construction, homeowners must consider various factors such as design, categorization, dimensions, and geographical setting. The overall cost will depend on these factors, but a sensible approach would be to consider the budget from a holistic perspective.

• Financing Costs

Loans or alternative financing mechanisms often carry interest rates and additional associated fees.

• Soft Costs

These encapsulate design and permitting fees, architectural charges, city-related expenses, and specialized evaluations, such as soil analyses and land appraisals.

• Build Costs

  • Vertical Build

The primary construction phase. To provide a benchmark, in places like San Diego, the average cost for this phase typically oscillates between $345 to $425 per square foot.

  • Site Work/Utilities

This encompasses land preparations, utility setups, and priming the site for construction.

  • Finishes

These are the final touches that define the ADU's internal and external appearance and ambiance.

Integrating an Accessory Dwelling Unit (ADU) into your property can be a smart investment decision. However, before diving into this project, it is essential to understand the regulations and intricacies involved in building an ADU. By taking the time to research and plan thoroughly, you can ensure that your project is successful and profitable in the long run.

Build with Multitaskr!

If you're planning to build an Accessory Dwelling Unit (ADU) in San Diego or Los Angeles, Multitaskr will guide you through every step of the process. Our team is committed to providing high-quality service and support from start to finish. Contact us today to schedule a consultation for your ADU project.

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