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What Is the Difference Between a House and an ADU?

California is in the middle of a housing shift, and more homeowners are asking an important question: what is the difference between a house and an ADU? Understanding this difference is essential for households who want to maximize their property, create more living space, or generate rental income. A house has always been the primary residence on a parcel, while accessory dwelling units (ADUs) are secondary structures that provide flexible, self contained living space. Both serve different functions, but each can contribute to affordable housing options, multigenerational living, and financial benefits for families across Sacramento, the Bay Area, and other cities in California.

What Is a House? accessory dwelling unit single family bay area

A house is a primary dwelling built as a single family home on its own lot. It is the main house intended for full time occupancy, designed with complete living space that includes a kitchen, bathroom, bedrooms, and separate rooms for daily function. Unlike ADUs, a house is not considered a secondary housing unit. It is the foundation of property ownership, subject to zoning regulations, building codes, and local regulations that govern density, setbacks, and construction.
A house typically offers larger square feet than an ADU, giving households more flexibility for family needs. For example, a 2,000 square foot single family home in Sacramento may include three bedrooms and two bathrooms, as well as a garage and outdoor space. Houses can be sold independently, refinanced at competitive interest rates, and inherited as a cornerstone of long term wealth.

What Is an ADU?

An ADU, or accessory dwelling unit, is a smaller residential structure built on the same property as the main house. Unlike a guest house that might be used for visitors temporarily, ADUs are intended as self contained living space with a kitchen, bathroom, and sleeping area. California law recognizes them as secondary housing units that expand affordable housing options. ADUs provide homeowners with the chance to generate rental income, house extended family, or create private space for guests.

Detached ADUs

Detached ADUs are backyard cottages or standalone structures built separate from the main house. These units provide complete living space with their own entrance, bathroom, and kitchen, making them suitable for long term renting or multigenerational living.

Attached ADUs

Attached ADUs share a wall with the main house. They are typically created by converting part of the existing structure or adding on new square feet. While they are close to the family home, they still have a separate entrance and provide private living space for guests or tenants.

Garage Apartments

Garage apartments are ADUs created by converting garages into livable rental units. These are popular because they repurpose existing structures into fully functional units, complete with a bathroom and kitchen, without the need for entirely new construction.

Junior ADUs (JADUs)

Junior ADUs are small units, typically under 500 square feet, located within the footprint of the main house. They might include a bedroom and kitchenette, and while they offer limited space, they can provide flexible living space for family members or guests.

7 Key Differences Between a House and an ADU

1 | Ownership and Legal Status

A house is a standalone property with clear legal status as the primary dwelling. An ADU shares the same property as the main house. However, with AB 1033, some California cities now allow ADUs to be sold separately as condominiums, creating new opportunities for investors and homeowners alike.

2 | Permits and Approval Timelines

Building a house requires extensive permits, long review periods, and full compliance with zoning regulations and building codes. ADUs, on the other hand, benefit from streamlined permitting. Cities must issue a decision within 60 days of receiving a complete application. This faster process allows households to complete ADU projects more efficiently than new home construction.

3 | Size, Space, and Setbacks

Houses are generally larger, offering thousands of square feet, multiple bedrooms, and bathrooms. ADUs are smaller, with typical sizes ranging from 400 to 1,200 square feet. Detached ADUs and garage apartments often have reduced setbacks and flexible height limits, making them easier to fit onto the same property.

4 | Parking and Access

Houses often require multiple parking spaces. ADUs, however, are limited to one space per unit or bedroom, and many qualify for parking exemptions. Most ADUs also have a separate entrance, giving tenants or guests privacy while sharing the same property.

5 | Fees and Ongoing Maintenance Costs

New houses face full development impact fees and higher ongoing maintenance costs. ADUs under 750 square feet are exempt from many impact fees, and even larger units typically pay less than a new home. Maintenance is still required, but households save compared to the costs of an entirely new property.

6 | Occupancy and Use

A house can serve any residential purpose. ADUs are restricted to residential use and are subject to limitations on short term rentals in many cities. Unlike ADUs, houses can always be rented or sold independently. However, ADUs allow homeowners to generate long term rental income while still keeping the main house intact.

7 | Financing and Property Value

Houses are financed with conventional mortgages and subject to full reassessment for property taxes upon sale. ADUs are often financed through home equity lines, renovation loans, or ADU-specific programs. Property taxes only increase based on the value of the new unit. For homeowners, this means ADUs contribute additional value without resetting the original tax base of the main house.

Benefits of Choosing an ADU Over a House

ADUs offer unique benefits that make them suitable alternatives to buying a second house.

• Financial benefits: Lower construction costs, reduced fees, and potential rental income.
• Multigenerational living: Provides space for family without needing a separate property.
• Affordable housing options: Expands housing supply across cities like Sacramento and the Bay Area.
• Flexibility: ADUs can function as guest houses, granny flats, or rental units.
• Long term value: ADUs increase the total living space and overall property value.

When Is a House the Better Choice?

Despite the advantages of ADUs, there are times when a house is more suitable. Families who need more square feet than ADUs allow, or households seeking independent ownership without shared land, may prefer a house. Investors who want to purchase properties in other cities for long term growth may also find that a house is the better project. Unlike ADUs, houses are not restricted by accessory dwelling unit regulations and can be sold freely.

How to Decide Between a House and an ADU

When comparing the difference between a house and an ADU, consider these factors:

• What is your budget and how much space do you need?
• Do you want rental income to offset costs?
• Are you providing homeowners in your family with multigenerational living space?
• Do you want to explore long term investing opportunities or short term housing solutions?
• What local regulations, permits, and zoning regulations apply to your property?
  Answering these questions helps homeowners make an informed decision. Golden State ADUs specializes in guiding Sacramento households through permits, design, and construction to ensure each project is suitable for their goals.

Frequently Asked Houses vs. ADUs Questions

Is an ADU considered a house in California?

No, an ADU is classified as an accessory dwelling unit, not a primary house. Its legal status is secondary, sharing the same property as the main house.

Can I sell my ADU separately from my house?

Yes, but only in cities that have adopted AB 1033 ordinances. This allows ADUs to be sold as condominiums, creating new opportunities for investors.

How much does it cost to build an ADU compared to a house?

ADUs typically cost less to build because they use the same property as the main house, require fewer permits, and have reduced impact fees.

Will building an ADU increase my property taxes?

Yes, but only based on the value of the new unit. The original house remains subject to its original tax assessment.

Do ADUs have separate entrances?

Yes, most ADUs are designed with a separate entrance to provide privacy for tenants or guests while still being attached to or near the main house.

Can I use my ADU as a guest house?

Yes, ADUs are suitable for housing guests, visitors, or family members, making them versatile units for homeowners.

Conclusion

The difference between a house and an ADU comes down to scale, legal status, and intended use. A house is the main dwelling on its own parcel, while an ADU is a secondary housing unit built on the same property as the primary residence. Houses typically require more permits, larger budgets, and longer construction timelines. ADUs are smaller, more flexible, and designed to contribute to California’s demand for affordable housing options. They offer ongoing financial benefits through rental income, increase living space for families, and provide long term value to households. Whether you want a guest house for visitors, a granny flat for aging parents, or rental units to generate income, an ADU may be the most suitable choice. Ready to explore what an ADU can do for your property? Golden State ADUs is Sacramento’s trusted partner for design, permits, and construction. Contact us today to make an informed decision about your future.