What Are the Different Types of ADUs?

What Are the Different Types of ADUs?

Accessory Dwelling Units (ADUs) have gained significant popularity in California and other parts of the United States. These secondary housing units on the same lot as a primary residence offer a versatile solution to various housing needs. 

As homeowners look to maximize their property’s potential, it is crucial to understand the different types of ADUs available.

Different Types of ADUs

This article delves into the various types of ADUs, their benefits, and suitable scenarios for each.

1. Detached ADUs

Definition and Characteristics

Detached ADUs are standalone units separated from the primary residence. These structures can be custom-built or pre-fabricated, ranging from tiny homes to larger guest houses. 

Detached ADUs often have their own entrance, kitchen, bathroom, and living area, providing complete autonomy from the main house.

Standard Designs and Construction Materials

Standard designs include single-story cottages, multi-story units, and modern tiny homes. Construction materials vary widely, from traditional wood and brick to contemporary steel and glass.


Privacy: Detached ADUs offer greater privacy for both the occupants of the ADU and the main house. This makes them an ideal choice for rental units or guest houses. 

Increased Property Value: Adding a detached ADU can significantly boost property value, making it a wise long-term investment.

Suitable Scenarios

Detached ADUs are particularly suitable for:

  • Multi-generational living: Providing a separate space for elderly parents or adult children.
  • Rental Income: Generating additional income by renting out the unit.
What Are the Different Types of ADUs?

2. Attached ADUs

Definition and Characteristics

Attached ADUs are connected to the main house but function as separate living units. They can be additions to the existing structure or conversions of part of the main house, like a wing or a basement.

Differences from Detached ADUs

Unlike detached ADUs, attached units share a wall with the primary residence, which can influence design and construction costs.


Cost-Effective Construction: Attached ADUs often require less construction work than detached units, making them more affordable. 

Space Efficiency: They are ideal for properties with limited space, as they do not require additional land.

Suitable Scenarios

The attached ADUs are ideal for the following:

  • Additional living space for family members.
  • Guest quarters or home offices.

3. Garage Conversion ADUs

Definition and Characteristics

Garage conversion ADUs involve transforming an existing garage into a livable dwelling unit. Depending on the garage’s location relative to the main house, this type of ADU can be either detached or attached.

Conversion Process and Potential Challenges

The conversion process typically involves adding insulation, plumbing, electrical systems, and sometimes a raised floor to meet residential standards. Challenges may include zoning regulations, structural changes, and parking considerations.


Cost Savings: Utilizing an existing structure reduces construction costs significantly. 

Preserve Yard Space: Since the garage footprint already exists, it doesn’t take away from yard or garden areas.

Suitable Scenarios

Garage conversion ADUs work well for:

  • Maximizing unused garage space.
  • Creating rental units without altering the main living space.
What Are the Different Types of ADUs?

4. Basement Conversion ADUs

Definition and Characteristics

Basement conversion ADUs involve converting an existing basement into a separate living unit. These ADUs are internal to the main house but can have their entrance.

Conversion Process and Potential Challenges

The conversion process includes waterproofing, installing proper egress windows for safety, and adding necessary utilities. Challenges may include low ceiling heights and ensuring adequate ventilation and natural light.


Efficient Use of Space: Converts underutilized basement space into a functional living area. Maintains Aesthetics: It does not alter the home’s external appearance, preserving its curb appeal.

Suitable Scenarios

Basement conversion ADUs are suitable for:

  • Urban areas with limited land availability.
  • Additional living quarters for family members or tenants.

5. Internal ADUs

Definition and Characteristics

Internal ADUs, also known as in-law units or granny flats, are created by reconfiguring the existing space within the main house. This can include converting attics and large rooms or adding a second story.

Key Features and Typical Designs

Key features include separate living areas, bathrooms, and sometimes small kitchens. Typical designs involve partition walls, additional staircases, or creating private entrances.


Minimal External Changes: As they are within the existing structure, internal ADUs require minimal changes to the exterior. Cost-Effective: Often cheaper to build since they utilize existing space and infrastructure.

Suitable Scenarios

Internal ADUs are best for:

  • Homes with underutilized internal spaces.
  • Creating an in-law suite for family members.
Types of ADU

6. Junior ADUs (JADUs)

Definition and Characteristics

Junior ADUs (JADUs) are smaller ADUs, typically at most 500 square feet. They are often created by repurposing a portion of the main house, like a garage or extra bedroom.

Legal Requirements and Size Restrictions

JADUs have specific size restrictions and must include an efficient kitchen and a separate entrance. They are often subject to local zoning regulations and may have fewer permitting requirements.


Affordability: Their smaller size makes JADUs more affordable to construct. Quick Construction: Their limited size allows for faster build times than larger ADUs.

Suitable Scenarios

JADUs are ideal for:

  • Creating a small rental unit for extra income.
  • Housing for a college student or young adult family member.

7. Modular ADUs

Definition and Characteristics

Modular ADUs are prefabricated units constructed off-site and then transported and assembled on the property. Depending on the design and site layout, these units can be detached or attached.

Differences from Traditional Construction

Modular construction involves building sections or modules of the ADU in a factory setting, which are then transported to the site for assembly. This differs from traditional on-site construction, which builds the unit from the ground up on location.


Faster Construction Time: Factory-built modules can be constructed quicker than traditional builds, reducing project timelines. 

High Quality: Factory settings allow for better quality control and precision in construction.

Suitable Scenarios

Modular ADUs are suitable for:

  • Rapid housing solutions, especially in areas with housing shortages.
  • Cost-effective builds due to economies of scale in factory production.
Types of ADU


ADUs offer a flexible and practical solution for various housing needs, from accommodating family members to generating rental income. Understanding the different types of ADUs—detached, attached, garage conversions, basement conversions, internal ADUs, JADUs, and modular ADUs—helps homeowners make informed decisions based on their specific circumstances and property characteristics.

Whether you’re looking to add a rental unit, create additional living space for family members, or increase your property’s value, there is an ADU type that can meet your needs. Consulting with professionals in ADU design and construction can further help you navigate options, and ensure sure our the project complies with local regulations and maximizes the benefits.

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