Find The Best ADU Contractors 
in San Diego County

An accessory dwelling unit relieves many problems and allows for a ton of flexibility of uses. People are building them to use as extra space (an office or guest house), a music or yoga studio, a mancave or she-shed, or a home for their retired parents or grown children.

The two primary options are either building a new unit in the backyard or converting an existing garage to an ADU. It can be attached to an existing home, attached to a garage in the rear of the lot, or detached completely.

In San Diego, a garage conversion ADU usually costs about $150,000 to $230,000 all-in, including plans, permits, city fees, and construction, with the construction alone typically running $120,000 to $150,000. A new detached ADU runs from about $190,000 for a 400 sq ft unit to $450,000 or more for 1,200 sq ft. Local builders price detached units at roughly $375 to $600 per square foot, and the smaller the unit, the higher the cost per square foot. Plans, engineering, and permits typically add another $10,000 to $18,000.

For a garage conversion, you can expect the entire process to take 5-6 months. A new accessory dwelling unit takes about 6-9 months total: 2-3 months for design and permits, then 3-6 months of construction. Permits can take longer when the City of San Diego or the County is backed up.

In the City of San Diego, ADUs are allowed on residential lots that have an existing or proposed home. A single-family lot can have one new ADU, one ADU converted from existing space, and one junior ADU, and the Bonus ADU program can allow up to 4 to 6 ADUs on some lots depending on lot size. Multifamily properties such as duplexes and apartment buildings can add ADUs too, including up to eight detached ADUs, as long as that doesn’t exceed the number of existing units.

When looking to build an accessory dwelling unit or even starting to explore the idea, it’s best to search for only local, licensed General Contractors. No other contractors are qualified or equipped to do this sort of construction, and using an unlicensed contractor or handyman would be a mistake.

Often, yes. Under California’s AB 2533, in effect since January 1, 2025, an unpermitted ADU or garage conversion built before January 1, 2020 can usually be legalized by meeting health and safety standards rather than every current code, and the city can’t charge penalties or impact fees to do it. A good contractor can inspect the unit and estimate the work involved. Learn more about this situation here: legalizing an unpermitted garage conversion.

It depends on the city and the utility. Many ADUs share the main home’s water and sewer lines, while others need a new water meter, a separate sewer lateral, or an electrical panel upgrade, which adds cost. San Diego Gas & Electric handles power across the county. Your contractor should confirm what your city and utilities require before pricing the job.

Not in most of the city. The City of San Diego requires no parking for an ADU outside the Coastal Overlay Zone, and none for a junior ADU. Bonus ADUs are the exception: each one needs a parking space unless the property is in a Transit Priority Area.

In some cases, yes. California’s AB 1033 lets cities allow an ADU to be split off and sold as a condominium, and both the City of San Diego (since August 2025) and unincorporated San Diego County (since spring 2026) have opted in. A sale requires a condominium map and meeting local rules, so talk to your contractor and a real estate attorney before you design with a sale in mind.

Yes, walking path access of 3’ wide is required from the front yard/sidewalk to the ADU (a driveway is acceptable).

No. You can rent both the main house and the ADU, and you don’t have to live on site. A junior ADU requires the owner to live on the property only if it shares a bathroom with the main house. In the City of San Diego, an ADU can’t be rented for less than 31 days in a row.

Expect roughly $8,000 to $18,000 in city and agency fees, depending on the jurisdiction and the size of the ADU, on top of plans and engineering. State law exempts ADUs of 750 sq ft or less from impact fees, though school fees still apply. The City of San Diego publishes its building permit fees in Information Bulletin 501.

Give us a call – we are happy to help! Too shy to say hello? Check out this blog with the 50 most frequently asked ADU questions from our clients: https://www.greatbuildz.com/blog/los-angeles-50-most-common-adu-questions/

An ADU housing unit becomes the optimum living arrangement in retirement in many respects. Having a house of one’s own helps a person to preserve independence and pride. And being on the same property and within a few feet of their family or support network is crucial when the need for assistance arises. This is especially true for retired individuals who opt to stop driving. Even though retirement is a delicate balance between independence and assistance, an ADU may be the best of both worlds.

It is probably a mistake to save money by operating as your own general contractor. Although you believe this may save you money, it’s a horrible idea unless you are really skilled or have a vast network of subcontractors (plumber, framer, roofer, foundation, electrical, stucco, drywall, etc,). When you choose an ADU contractor (or general contractor), you are not only paying them to oversee the project, but also for their relationships with the crew, employees, and subcontractors who can complete the project successfully. It is quite difficult for you to find skilled tradespeople. And if one of these contractors performs poorly, you will have to pay twice to repair their errors.

Regardless of the specifics of your project, you should pay your ADU contractor a reasonable fee. Obtain three to five bids from various ADU contractors prior to making a final decision. If all of the bids are somewhat comparable in price, it indicates that your project is ‘clear’ to each contractor and that their pricing is likely in line with the market. However, if your estimates are inconsistent, it indicates that something is wrong. Either your project’s specifications are unclear, or your contractors’ bids are unrealistically high or cheap. In this instance, obtaining several bids will assist you determine the job’s suitable pricing.

ADU investments have become an appealing financial prospect for investors. Real estate investors or first-time investors previously chose to purchase a duplex or triplex, but now have a new alternative. The ADU investment opportunity is quite straightforward: buy a single-family house with the option to add an ADU and/or junior ADU, and construct one or both. This ADU investment has transformed the property from a single-family dwelling to a duplex or triplex. An ideal property has sufficient backyard space or a detached garage that can be transformed into an ADU. Now, the ADU investor may rent the units to numerous tenants and generate several streams of rental revenue from a single property.