Accessory Dwelling Units Explained: What, Why, and How


The Benefits of Accessory Dwelling Units (ADUs)

When you come across the term “what is an accessory dwelling unit”, you might imagine a small, independent living space nestled on the same property as a larger home. Imagine a compact yet fully functional apartment that provides everything a regular home would – a kitchen, bathroom, sleeping area, and living space.

Here’s a quick overview of what is an accessory dwelling unit:

  • Definition: An ADU is a secondary, self-contained living unit on the same lot as a primary residence.
  • Features: ADUs have their own kitchen, bathroom, and living space.
  • Types: They can be detached, attached, or part of the main house like a converted garage or basement.
  • Purpose: They provide flexibility, such as rental income or housing for family members.

ADUs have been around for centuries, known by various names like granny flats, in-law suites, and carriage houses. Historically, they have provided a practical solution for multigenerational living and affordable housing. Today, they offer a versatile way to enhance property value, generate rental income, or accommodate family needs.

I’m Michael Kootchick, a real estate developer with years of experience in creating and managing ADUs. My background has given me a deep understanding of what is an accessory dwelling unit and how it can benefit homeowners.

ADU Overview Infographic - what is an accessory dwelling unit infographic pillar-4-steps

What is an Accessory Dwelling Unit?

An Accessory Dwelling Unit (ADU) is a small, self-contained living space located on the same property as a single-family home. These units are designed to provide additional housing options without the need to purchase a new property. They come equipped with their own kitchen, bathroom, and living area, making them independent from the main house.

Types of ADUs

ADUs come in various forms, each offering unique benefits. Here are the most common types:

1. Detached ADU:
A standalone unit, often referred to as a backyard cottage or granny flat. These are completely separate from the main house and usually located in the backyard.

2. Attached ADU:
An addition to the main house, like a bump-out or an extension. These units share a wall with the primary residence but have their own separate entrance.

3. Internal ADU:
A section of the main house that is partitioned off to create a separate living space. This could be a converted basement or attic.

4. Garage Conversion:
An existing garage transformed into a living space. This type of ADU is popular for its cost-effectiveness and efficient use of existing structures.

5. Basement Conversion:
An underutilized basement converted into an independent living area. This type is ideal for properties with ample basement space.

Legal Aspects

Building an ADU involves navigating various legal requirements, including zoning laws, building codes, and permits. Understanding these aspects is crucial for a smooth construction process.

Zoning Laws:
Zoning laws determine where ADUs can be built. These rules vary by location and can dictate the size, height, and placement of the unit. For instance, some areas may require a minimum lot size or limit the number of ADUs per property.

Building Codes:
Building codes ensure that the ADU is safe and habitable. These regulations cover everything from electrical wiring to plumbing and structural integrity. Compliance with building codes is mandatory to obtain construction permits.

Securing the necessary permits is a critical step in building an ADU. This process involves submitting architectural plans and meeting local building standards. Permits ensure that the construction meets all legal and safety requirements.

Case Study:
In Portland, Oregon, ADUs have become a popular way to increase housing density without altering the character of neighborhoods. The city has streamlined the permitting process, making it easier for homeowners to build these units. Similarly, California has passed laws to simplify ADU construction, addressing the state’s housing shortage.

By understanding what is an accessory dwelling unit and the various types and legal aspects involved, homeowners can make informed decisions about adding an ADU to their property. This knowledge sets the stage for exploring the benefits and use cases of ADUs, which we’ll delve into next.

Why Consider an Accessory Dwelling Unit?

Adding an accessory dwelling unit (ADU) to your property can be a game-changer. Let’s explore the benefits, use cases, and financial advantages of ADUs.

Benefits of ADUs

Flexibility: ADUs offer flexible living arrangements. Whether it’s a detached unit or a basement conversion, they can adapt to various needs.

Rental Income: One of the biggest perks is the potential for rental income. Renting out an ADU can provide a steady income stream, helping to cover mortgage payments or other expenses.

Multigenerational Living: ADUs are great for multigenerational families. They allow elderly parents to live independently while staying close to family, often referred to as “granny flats.”

Property Value: Adding an ADU can significantly increase your property’s value. A well-designed ADU can make your home more attractive to future buyers.

Use Cases

Family Housing: ADUs can serve as housing for family members. This is particularly useful for aging parents or adult children who need a place to stay.

Rental Units: Many homeowners use ADUs as rental units to generate additional income. This can be especially beneficial in high-demand rental markets.

Caregiver Housing: If you need a live-in caregiver, an ADU provides a separate, comfortable living space for them. This ensures privacy for both the caregiver and the family.

Financial Advantages

Cost Efficiency: Building an ADU is often more cost-effective than buying a new property. Utilizing existing space, like a garage or basement, can save on construction costs.

High ROI: The return on investment (ROI) for ADUs can be substantial. For example, in California, a $100,000 ADU could generate $1,200 to $2,200 in monthly rent, easily covering the additional property taxes and then some.

Tax Benefits: You can also take advantage of tax benefits. For instance, expenses related to building and maintaining the ADU can be deducted if it’s used as a rental property. Depreciation of the ADU itself can also be written off over 27.5 years.

By understanding these benefits, use cases, and financial advantages, you can see why ADUs are becoming a popular choice for homeowners. Next, let’s dive into how to build an ADU, covering planning, design, and the construction process.

How to Build an Accessory Dwelling Unit

Planning Your ADU

Building an Accessory Dwelling Unit (ADU) starts with careful planning. This phase involves several key steps:

Site Assessment: First, evaluate your property to determine the best location for your ADU. Consider factors like lot size, existing structures, and access to utilities. A feasibility study can help identify any potential challenges.

Zoning Requirements: Check your local zoning laws. Different areas have different regulations for ADUs. For example, some cities may require a minimum lot size or additional parking spaces. It’s crucial to ensure your plans comply with these rules to avoid fines or delays.

Budgeting: Create a detailed budget. Include costs for permits, design, construction, and any necessary professional services like engineers or surveyors. That building an ADU can increase your monthly utility bills and property taxes.

Designing Your ADU

Once your planning is in place, the next step is designing your ADU. Here are some key considerations:

Architectural Plans: Develop detailed architectural plans. These should include the layout, dimensions, and specifications for materials. It’s often helpful to hire an architect or designer experienced with ADUs.

Styles: Choose a style that complements your primary home. Popular options include Contemporary, Craftsman, and Spanish/Mediterranean. Your choice will affect both the aesthetic and functionality of the unit.

Customization: Think about who will use the ADU. If it’s for an elderly family member, consider features like wheelchair accessibility and grab bars. If it’s a rental unit, ensure it has a separate entrance and adequate privacy.

Construction Process

The construction phase involves several steps, from obtaining permits to final inspections:

Permits: Before breaking ground, you need to secure the necessary permits. This can be a complex process, as each city has its own requirements. Typically, you’ll need to submit your plans to the city’s planning department for approval. Be prepared for possible revisions and a waiting period.

Contractors: Hire reputable contractors. Get multiple bids and check references. Make sure your contractors are familiar with local building codes and have experience with ADUs.

Timeline: Develop a realistic timeline. Construction can take anywhere from a few weeks to several months, depending on the complexity of the project. Regularly communicate with your contractors to ensure the project stays on schedule.

Inspections: Throughout the construction process, your ADU will need to pass various inspections. These ensure the unit complies with building codes and safety standards. Plan for these inspections to avoid delays.

By following these steps, you can successfully navigate the process of building an ADU. Next, let’s address some frequently asked questions about ADUs, including potential drawbacks and legal considerations.

Frequently Asked Questions about Accessory Dwelling Units

What’s one drawback of an ADU?

Space Limitations: One common drawback of an accessory dwelling unit (ADU) is space constraints. Local regulations often dictate the maximum size of an ADU, which can be as small as 750 square feet or a percentage of the main house’s square footage. This limited space can pose challenges for design and functionality. However, smart design solutions like built-in storage and multi-functional furniture can help make the most of the available space.

Privacy Concerns: Another potential issue is privacy. Since ADUs share a lot with the primary residence, maintaining privacy for both units can be tricky. Simple solutions like strategic landscaping, privacy screens, and soundproofing can help mitigate these concerns.

What is another name for an accessory dwelling unit?

ADUs go by many names, each conjuring a different image. Here are a few commonly used terms:

  • Granny Flats: Often used to describe small, standalone units perfect for elderly family members.
  • In-Law Units: These are typically attached to the main house and provide a separate living space for extended family.
  • Backyard Cottages: Detached units located in the backyard, offering a cozy, independent living space.

These alternate names help people better understand the concept and potential uses of ADUs. Whether you call it a granny flat, in-law unit, or backyard cottage, the benefits remain the same: flexible living spaces, additional rental income, and the ability to keep family close by.

By understanding these frequently asked questions, you can better navigate the complexities of adding an ADU to your property. Next, let’s explore the financial advantages of ADUs.


Accessory Dwelling Units (ADUs) offer a versatile and practical solution for modern housing needs. They provide flexible living spaces, generate rental income, and support multigenerational living. Whether it’s an attached unit, a detached cottage, or an internal apartment, ADUs can greatly enhance the functionality and value of your property.

OneStop ADU: Your Partner in ADU Development

At OneStop ADU, we simplify the entire process of creating your own ADU. From initial property evaluation to design, permitting, and construction, we handle everything to ensure a smooth and efficient experience. Our San Diego ADU services are designed to meet your unique needs, offering pre-designed plans or customized solutions.

Why Choose OneStop ADU?
Comprehensive Services: We manage all aspects, including zoning, design, and construction.
Fixed Pricing: Know exactly what your ADU will cost.
Guaranteed Timelines: We promise on-time completion.

Future Trends in ADUs

The future of ADUs looks promising. With increasing housing demands and changing family dynamics, more homeowners are exploring ADU options. Additionally, new zoning laws and government programs, like New York State’s Plus One ADU Program, are making it easier for homeowners to add these units.

Key Trends to Watch:
Sustainable Designs: Expect more eco-friendly and energy-efficient ADU designs.
Technological Integration: Smart home features will become more common in ADUs.
Policy Support: Continued government incentives and zoning reforms will promote ADU development.

By staying informed and choosing the right partner, you can leverage these trends to create a valuable and adaptable living space on your property.

Ready to explore the possibilities? Visit our San Diego ADU services page to get started on your ADU journey with OneStop ADU. Let’s create a flexible, valuable, and sustainable living space together.


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