San Diego ADU Builders

Under San Diego’s 2025 rules, a single-family lot can typically accommodate one Junior ADU (JADU) plus two ADUs—one converted from existing space and one newly built detached unit (Inside San Diego). The City also offers an ADU Bonus Program, allowing additional units when at least one is deed-restricted as affordable (City of San Diego). However, mid-2025 reforms limited its scope: the bonus program is now prohibited in low-density single-family zones and capped by lot size—for example, no more than four total units on lots under 8,000 sq. ft.. Bottom line: you can always build at least one ADU (plus a JADU) by right, but if you’re considering multiple units, check current zoning and bonus program rules first.

There is no minimum lot size requirement to build an ADU in San Diego. California state law prohibits cities from imposing lot size minimums for ADUs (CA HCD ADU Handbook), meaning even small residential lots may add an ADU if they meet other standards like setbacks and height. By code, the smallest ADU must be at least 150 sq. ft. (the minimum efficiency unit size). In San Diego, the maximum ADU size is 1,200 sq. ft., depending on zoning and lot coverage (City of San Diego). So, even on compact city lots, homeowners can typically add an ADU as long as they respect local building and safety codes.

Yes, coastal properties in San Diego follow additional rules. If your property lies in the Coastal Overlay Zone, many ADUs will require a Coastal Development Permit (CDP), especially if they add new square footage such as a detached unit or an addition (City of San Diego). Conversions within existing structures or JADUs may sometimes be exempt. Since September 7, 2022, the City has authority to issue ministerial CDPs for ADUs in non-appealable areas, allowing a streamlined approval similar to a building permit. However, if your lot is in an appealable area—often closer to the shoreline or in sensitive zones—the CDP process can involve more review and Coastal Commission oversight. In short, state ADU law still applies in the coastal zone, but you should budget extra time for a CDP where required.

In 2025, building an ADU in San Diego typically costs $350,000–$500,000+ for a detached unit of 700–1,200 sq. ft., which translates to about $375–$600+ per sq. ft. depending on sitework, utilities, and finishes (ADU Insider; Jean Prescott). Smaller projects or conversions can range $150,000–$300,000+, with garage conversions generally costing less than ground-up builds (Lifehouse SD). All-in budgets include design, engineering, permits, site prep, and utilities, with fees in San Diego typically adding $6,500–$21,000 depending on size (Better Place; City of San Diego Fee Bulletin). State law still waives impact fees for ADUs ≤750 sq. ft., which can save tens of thousands (CA HCD). Bottom line: plan conservatively at the mid-to-high range, then value-engineer with standard plans and early utility coordination to keep costs predictable.

In 2025, most San Diego ADUs take about 10–16 months from first consultation to move-in, with construction itself averaging 6–12 months once permits are issued. The timeline typically includes 4–8 weeks for pre-design and feasibility, 2–4 months for permitting under California’s 60-day review mandate, and 6–12 months of on-site build depending on site conditions, utilities, and scope. San Diego also offers a 30-day expedited review for projects using pre-approved standard plans, which can shorten the overall schedule. Detached backyard cottages usually run closer to 12 months door-to-door, while garage conversions and interior ADUs may finish faster. Complex sites, service upgrades, or coastal permits can extend the process, so planning with complete intake documents and early utility coordination is key (San Diego Housing Commission).

No, an ADU in San Diego cannot encroach into the front yard. The City requires ADUs to observe the standard front yard setback of the property’s zoning district, meaning you cannot build an ADU closer to the street than where the main house could be placed (City of San Diego). However, ADUs do benefit from reduced side and rear setbacks—as little as 0–4 feet depending on height and fire zone—consistent with California state law. In practice, this means ADUs are typically located in the backyard or side yard, but never encroaching into the front setback area.

In most cases, no parking is required for ADUs in San Diego. City code confirms that off-street parking spaces are not mandated for ADUs, except in a specific coastal scenario (City of San Diego). If your property is outside the Coastal Overlay Zone, zero parking spaces are needed. Within the coastal zone, parking is only required if you are in the Beach Impact Area and also outside a Transit Priority Area—in that case, one space per ADU is required. Even then, exceptions apply: units under 500 sq. ft. or properties near car-share vehicles are exempt. Additionally, if you convert an existing garage to an ADU, the City cannot require you to replace those lost parking spaces. The bottom line: nearly all ADUs in San Diego, especially those in urban and suburban neighborhoods, have no parking requirement.

If your property is in a High or Very High Fire Hazard Severity Zone, special ADU rules apply. As of 2025, ADUs must maintain at least a 4-foot side and rear setback, even for single-story units under 16 ft tall, to create defensible space (City of San Diego). For projects using the ADU Bonus Program, lots in these fire zones must front a public street with two separate evacuation routes—bonus ADUs are not allowed on cul-de-sacs or single-access roads. In addition, while standard ADUs don’t require sprinklers if the main home doesn’t have them, bonus or affordable deed-restricted ADUs must include sprinklers. These rules, along with wildfire-resistant construction standards, are designed to ensure safety and compliance in San Diego’s high-risk fire areas.

When building an ADU in San Diego, expect to pay standard permit and school fees, but there are key exemptions that save costs. Development impact fees are waived for ADUs under 750 sq. ft., and larger ADUs only pay fees proportional to their size (City of San Diego). Utility connection fees apply if a new water or sewer connection is required, but San Diego offers a 50% reduction on capacity charges for ADUs, and conversions that don’t need new connections avoid these fees entirely . School fees are exempt for units under 500 sq. ft., but apply to larger ADUs (e.g., ~$4.80 per sq. ft. in San Diego Unified as of 2024). Permit fee waivers that once existed have expired, though the 2025 ADU Bonus Program now imposes a small “community enhancement” fee for affordable or bonus ADUs under 750 sq. ft. Bottom line: small and conversion ADUs enjoy major fee savings, making them one of the most cost-effective ways to add housing in San Diego.

Yes—San Diego offers pre-approved ADU plans that can significantly speed up permitting. Under AB 1332 (2023), cities must provide faster approvals for ADUs using state- or city-sanctioned standard plans. San Diego accepts free County of San Diego ADU plans, as well as pre-approved designs from Chula Vista and Encinitas. When you apply with one of these plans, the City provides a streamlined 30-day review instead of the typical 2–3 months. You’ll still need to ensure the design fits your site and license the plan from the creator, but this option removes most of the uncertainty and saves significant time.

Most ADU permits in San Diego take about 2–3 months for approval, thanks to California’s rule requiring cities to act on ADU applications within 60 days of a complete submittal (CA HCD). In practice, simple projects can get through in that time, while more complex sites (coastal, hillside, or with multiple correction cycles) may take closer to 3–4 months. San Diego also offers an expedited 30-day review for applications using pre-approved ADU plans (County of San Diego), which can significantly speed things up. Always plan for some buffer, but with proper preparation and experienced guidance, permit approval is typically much faster today than in years past.