ADU vs Tiny Home in San Diego: Key differences explained

Across San Diego, homeowners are exploring new ways to add housing, create flexible space, or live more efficiently. Two popular options that often come up are Accessory Dwelling Units (ADUs) and Tiny Homes.

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Although they can look similar from the outside, there are key differences in how they’re built, permitted, and used. Understanding these distinctions can help homeowners decide which option best fits their goals, budget, and property type.

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What Is an ADU?

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An Accessory Dwelling Unit (ADU) is a secondary housing unit built on the same property as a main home. It can be attached to the main residence, detached in the backyard, or created by converting existing space—such as a garage.

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ADUs are recognized under California state housing laws and must comply with all local building, fire, and zoning codes. They include their own kitchen, bathroom, sleeping, and living space, making them fully functional homes.

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Because ADUs are built on permanent foundations and connected to utilities, they are treated as permanent residential structures and can legally be used for long-term occupancy.

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What Is a Tiny Home?

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A Tiny Home is smaller—typically between 100 and 400 square feet—and designed for efficient living. They come in two main types:

• Tiny Homes on foundations, which are stationary and can sometimes qualify as permanent residences if they meet local building standards.
• Tiny Homes on wheels (THOWs), which are mobile and often classified similarly to recreational vehicles (RVs) under California law.

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Tiny homes are known for their minimalist design, compact size, and flexibility. However, how they’re used in San Diego depends heavily on zoning and permitting regulations.

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How San Diego Classifies ADUs vs. Tiny Homes

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In San Diego, ADUs are fully permitted residential units under both state and local law. They can be rented out long-term, provided they meet the city’s development standards and permit requirements.

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Tiny homes, especially those on wheels, fall under different rules. A movable tiny home may be allowed in limited areas, such as RV parks or certain zoning designations, but it typically cannot serve as a permanent dwelling on a residential lot. For a tiny home to qualify as a legal residence within San Diego city limits, it must be built on a foundation and meet the same building and safety standards as other residential structures—including ADUs.

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Construction and Foundation

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ADUs are constructed much like traditional homes. They sit on permanent foundations, go through plan review and inspection, and are connected to utilities such as water, sewer, and electricity.

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Tiny homes can be built either on wheels or on a foundation. A tiny home on wheels offers flexibility and mobility but is not considered a permanent structure. One on a foundation may meet building codes but must still align with zoning regulations to be legally occupied.

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Cost and Financing

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The cost difference between ADUs and tiny homes can be significant.

• ADUs in San Diego generally range from $150,000 to $300,000+, depending on size, finishes, and site conditions. They can often be financed through home equity loans, construction loans, or ADU-specific programs.
• Tiny homes usually range between $30,000 and $80,000, depending on design and whether they’re built on wheels or a foundation. However, financing options for tiny homes are more limited since they are often classified as personal property rather than real estate.

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While ADUs involve higher upfront costs, they are considered permanent improvements to the property, whereas tiny homes may not impact the property’s assessed value.

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Size and Design

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ADUs can be up to 1,200 square feet in San Diego (depending on zoning), providing ample space for a one- or two-bedroom layout suitable for long-term living.

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Tiny homes, by design, prioritize compactness and simplicity, typically ranging from 100 to 400 square feet. They are often chosen for minimalism, mobility, or temporary housing solutions.

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Permits and Utilities

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An ADU requires city permits, inspections, and permanent utility connections. This ensures the unit meets all safety, building, and zoning requirements.

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A tiny home on wheels does not go through the same permitting process unless it’s reclassified as a permanent structure. Instead, it typically uses temporary or off-grid utility systems. A tiny home built on a foundation would need the same permits and utility connections as an ADU.

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Pros and Cons Explained

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ADU Pros:

ADUs are fully legal residential units under San Diego’s zoning and state housing laws. Because they’re built on permanent foundations, they’re eligible for long-term occupancy, rental use, and property integration.

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ADU Cons:

Building an ADU involves more planning, permitting, and upfront cost compared to a tiny home. The construction process is longer and requires adherence to detailed building standards.

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Tiny Home Pros:

Tiny homes are generally quicker and less expensive to build. They appeal to homeowners seeking a simple, flexible, or mobile living space, and they often come with lower utility needs and environmental impact.

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Tiny Home Cons:

Tiny homes—especially on wheels—may not qualify for long-term residential use under San Diego regulations. They can face zoning restrictions, limited financing options, and may not add value to the property since many are not classified as real estate.

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Which Option Is Right for You?

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Choosing between an ADU and a tiny home depends on your goals:

• If you want a permanent residence that complies with San Diego building codes and can be legally rented, an ADU may be more suitable.
• If your priority is mobility, lower costs, or temporary use, a tiny home might offer more flexibility.

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Both options represent innovative approaches to creating more livable, efficient spaces within San Diego’s housing landscape—it’s simply a matter of determining which aligns best with your property and lifestyle.