ADUs, Granny Flats, or Casitas

Accessory Dwelling Units (ADUs), Granny Flats, and Casitas

In response to San Diego’s housing shortage, the city is working on making it easier and cheaper to build granny flats or accessory dwelling units (ADU). An ADU is a great way to offset the cost of your home, take advantage of the high cost of rent in San Diego County, or give yourself a little more privacy if you have a multigenerational home.


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What is a Granny Flat?

Although it is called a granny flat, it doesn’t mean your grandma has to live there. They are often used by grandparents, young adult children, nannies, houseguests, and (depending on zoning laws) renters.

For San Diego County zoning purposes, they are called accessory dwelling units (ADU). An ADU is a secondary, self-contained living area built on the property of a single-family home. Sometimes they are also called casitas, guest houses, mother-in-law units, pool houses, in-law apartments, bonus units, accessory apartments, or secondary living units.

They usually have a kitchenette, bathroom, and private entrance. Depending on the size and design, they may be all one room like a studio apartment or they can have a bedroom and separate living area.


How Much Does it Cost to Build an ADU in San Diego?

An ADU is a great investment in your home, but you will want to make sure you are well aware of the costs. Even for a small space, you will need to add electrical, plumbing, and heating. Plus, you will need to budget for a bathroom and kitchenette.

That is why building an ADU can cost $300 to $600 a square foot depending on the degree of difficulty, where the build out is going, and whether or not it is two-story. This does not include permit fees.


What are my Design Options for a Granny Flat?

A granny flat can be attached or detached from your home. Sometimes it can be added on over the garage or the garage can be converted to a granny flat. If there is room in the back or front yard, it can be added as a detached unit. The recent tiny house movement has been a real boon, making more space-saving and attractive designs available to homeowners.

If an elderly family member will be using the ADU, you will want to make sure the secondary living unit is accessible to seniors. TR Construction also specializes in aging in place remodeling and can help bring the unit in line with universal design or accessible design principles.


What are San Diego County’s Zoning Laws for ADUs?

Recent changes in California state law have made it much easier to build an ADU. You will still require a building permit, but the fees have been dramatically lowered and the approval process is now much easier. However, the ADU cannot be used as a vacation rental. To prevent the building of vacation rentals, any leases for ADUs cannot be for less than 30 days.

According to San Diego County, “An ADU attached to a primary dwelling may be up to 50% of the size of the single-family residence, up to a maximum of 1,200 square feet. An ADU detached from the single-family residence may be up to 1,200 square feet, regardless of the size of the residence.” San Diego County also has resources available to homeowners to help streamline construction and approval.

For more information about San Diego County and surrounding cities guidelines
San Diego County General ADU Guidelines and Frequently Asked Questions
San Diego County Comprehensive List of ADU Requirements
City of San Diego Companion/Junior Units
City of Poway ADU Fact Sheet (PDF)


San Diego ADU Builders

TR Construction has been working in San Diego County since 1994. We very familiar with the zoning laws and can help guide you in the process of building your own ADU. If you would like more details about granny flats and the required steps for building one in San Diego, please give us a call at (858) 537-6490.

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In The News – Follow San Diego County’s Move Towards More ADUs
San Diego Housing Commission launches program to spur granny flat production
Making It in San Diego: Granny flat permits soar
Board of Supes Waive Permit Costs, Fees for ‘Granny Flats’ for Next Five Years to Address Housing Shortage
San Diego may offer homeowners loans to build affordable housing


ADU Project Gallery