Building a Granny Flat in San Diego: What Homeowners Should Know
Many homeowners in San Diego are looking at granny flats — also known as accessory dwelling units (ADUs) — as a practical way to add usable space and increase property value. SJB Construction Inc works with homeowners navigating this process, from understanding local regulations to completing the build. These self-contained living areas are commonly used to house aging parents, adult children, or long-term tenants.
San Diego County has been dealing with a housing shortage, and in response, the San Diego Board of Supervisors voted to waive permitting fees for ADUs. This has made it a more financially accessible time to consider building a granny flat or detached ADU in the area.
Can You Build an ADU on Your Property?
Before moving forward, it's important to determine whether your property qualifies. In San Diego, an ADU — sometimes referred to as a companion unit (CU) — can be either attached to the main home or detached, such as a backyard cottage or converted garage. There are several regulations that apply:
- The unit must be located in a residential zone where a single-family residence exists or is being built.
- It must be on the same legal lot as the primary dwelling.
- It cannot be sold separately from the main home.
- It must include space for sleeping, sanitation, eating, and living.
- It must comply with fire and main building setbacks.
- A compliant parking space must be provided.
In some cases, an existing structure can be converted into an ADU. However, properties zoned as multi-family units may not qualify. City and county regulations can also differ, so it's worth verifying the rules that apply to your specific address before starting any project.
As for size, a detached ADU can be up to 1,200 square feet. If the unit is attached to the main home, it must not exceed 50 percent of the existing dwelling's floor area. Common locations for granny flats include basements, existing garages, above garages, or as standalone structures on the property.
What Does It Cost to Build a Granny Flat in San Diego?
Construction costs vary depending on the scope of the project, but the minimum is generally around $250 per square foot. Several factors can push that number higher:
- Expanding an existing structure or building from scratch
- Adding new power, sewer, or electrical connections
- Building on a second story
- Laying a new foundation, constructing exterior walls, or adding a roof
- Challenging on-site conditions
The cost per square foot for an ADU tends to be higher than for a standard single-family home. This is largely because the build still requires the most expensive rooms — a kitchen and bathroom — without the ability to offset those costs by adding larger living areas or additional bedrooms.
Some homeowners consider prefabricated or modular units as a way to reduce costs. However, the advertised price per square foot from modular companies typically doesn't include planning, permitting, site grading, foundation work, sales tax, or transportation fees. Additionally, not all sites are eligible for factory-built dwellings.
On the positive side, the fee waiver program in San Diego County can result in significant savings. With developmental impact fees also being waived, some homeowners may save an estimated $14,000 or more compared to building outside this period. The San Diego Union-Tribune has reported that the waiver can represent roughly a 50 percent discount on typical fees, which can range from $30,000 to $49,000.
As an investment, a granny flat can add meaningful value to a property. With the average price per square foot for a San Diego home sitting around $446, adding approximately 600 square feet of living space could increase a home's resale value by around $200,000.
SJB Construction Inc assists homeowners throughout the San Diego area with granny flat construction, garage conversions, and detached ADU builds. They can help assess your property, walk through the regulatory requirements, and provide guidance on what a project might realistically involve.
