A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable ADU Builders Across San Diego
Adding an accessory dwelling unit in San Diego typically costs between $180,000 and $420,000 for a custom detached build, with prefab installations landing closer to $140,000 – $280,000. Those are real numbers for this market, not national averages. We know San Diego lots, San Diego inspectors, and the particular headaches that come with canyon slopes, coastal marine layers, and homes built before current seismic codes. If you’re weighing a detached ADU, a garage conversion, or a JADU above an existing garage, call (619) 376-2760 and we’ll walk the property with you, write up a real price, and put the whole thing in writing before any work begins.
Key takeaways
- A custom detached ADU in San Diego runs roughly $180,000 – $420,000 depending on site conditions, foundation work, and finish level.
- Prefab and modular ADUs using brands like Boxabl, Plant Prefab, and Tuff Shed can bring the build window down to 6 – 9 months instead of 12 – 14.
- Russell Delmar leads our San Diego operation, and every project carries the 365-Day Done Right Promise in writing.
- The 2020 bonus ADU program makes San Diego one of the most ADU-friendly large cities in California, but canyon-lot geotech still governs what actually gets approved.
Why Lodgewick ADU San Diego Is San Diego’s Preferred ADU Builders Company
Most San Diego homeowners have heard a contractor story that ended badly. A price that crept up after the wall came down. A crew that vanished for three weeks. A “finished” project that leaked the first winter. Russ Delmar started this San Diego operation under the Kingswell family’s ADU division specifically to run projects differently. That means a written price before the first hole is dug, a defined arrival window on every visit, and a clean job site at the end of each day. The Kingswell Guarantee is not a verbal promise. It’s a written document you get before work starts, and it includes a free return visit if anything fails within 365 days of completion.
We’re not a franchise juggling forty cities. This San Diego office coordinates scheduling and dispatch locally, and our ADU Builders team handles every job from first site visit to final inspection. When you call (619) 376-2760, a live person answers. No voicemail tree, no “press 2 for new projects.” That matters at 7 AM when a concrete truck is fifteen minutes out or at 9 PM when you have a question about a change order.
ADU Construction in San Diego
ADU construction in San Diego means building a second dwelling unit on a lot that already has one home. It’s the most direct way to add rental income, create a place for aging parents, or give an adult kid a path out of paying San Diego rents. In this city, ADU construction is shaped by something no other large California market deals with quite the same way: thousands of houses built between the 1950s and 1980s on canyon edges and hillsides where flat ground is scarce and the geology under your feet varies block by block. A simple backyard ADU on a flat Clairemont parcel is a different project than one perched above a slope in Point Loma.
Site evaluation comes before anything else
Before we quote an ADU in San Diego, we look at slope, soil, access, and the existing home’s structural condition. On canyon lots especially, what you see at street level rarely matches what’s happening at the rear property line. We measure, we soil-test where needed, and we figure out whether your hillside triggers a geotech report before the city will even review plans. That step alone can change the foundation design completely.
Permits, drawings, and the San Diego review process
San Diego’s Development Services Department has streamlined ADU review in recent years, but each neighborhood has its own quirks. The coastal height-limit exemptions vary by overlay zone, and fire-resistant construction requirements kick in for chaparral-adjacent neighborhoods. We prepare plans that reflect your exact site, submit with complete documentation, and handle plan-check corrections without leaning on you to chase the city.
Detached ADU in San Diego
A detached ADU in San Diego is a standalone second home in your rear yard, with its own kitchen, bathroom, entrance, and address-adjacent sensibility. On a standard 5,000 – 7,000 sq ft San Diego lot, a detached ADU typically runs 500 – 800 square feet and costs between $180,000 and $420,000 when built stick-by-stick on site. The wide range is real. Flat lots with straightforward access and conventional slab foundations sit at the lower end. Hillside lots with retaining walls, pier-and-grade-beam foundations, and limited equipment access climb toward the top. Prefab options from Plant Prefab or Boxabl can compress both the cost and the timeline, provided your site can accept a crane or a flatbed delivery.
Foundation realities on San Diego hillsides
There’s no single “standard” foundation for a detached ADU in San Diego. On stable ground in Mira Mesa or North Clairemont, a thickened-edge slab works fine. On Santa Fe Formation clay or canyon fill, you may need deepened perimeter footings, helical piers, or both. We bring in a soils engineer when the conditions call for it, and the cost of that report and any foundation overbuild is written into your estimate before you sign anything.
What a detached ADU includes
Beyond the structure itself, a detached ADU in San Diego requires its own subpanel, water service, sewer lateral, and often a separate gas drop. If your existing sewer line is cast iron from the 1960s, the city may require replacement of the section your ADU taps into. We include those line items in the written price. You’ll never get a change order sprung on you at the drywall stage without prior written approval.
Trusted Brands We Service in San Diego
We install and assemble prefab and modular ADU systems from Boxabl, Plant Prefab, and James Hardie siding is a standard exterior finish on many of our San Diego builds. Because our San Diego office orders directly through established supply channels, San Diego customers don’t wait weeks for parts when a panel or window needs replacing mid-build. We also work with Tuff Shed structures when a homeowner wants a shell-and-finish approach, though we’re clear about what a garden shed is versus what gets permitted as an ADU. If you’ve already bought a kit or a factory-built module, we’ll handle site prep, permits, utility connections, and final inspection.
Common ADU Builders Problems We See in San Diego Homes
- Legacy unpermitted work. In neighborhoods like North Park and Normal Heights, garage conversions were done decades ago without permits. Today’s city requires that work be legalized or corrected before a new ADU can proceed on the same lot. We find this early, tell you straight, and build the fix into the plan rather than discovering it mid-demolition.
- Undersized foundations on canyon fill. A 4-inch unreinforced slab poured directly on loose soil is common in 1960s-era San Diego construction. It was fine for a carport. It will not support a living unit, and it will fail inspection. We test before we assume.
- Fire-resistant construction codes. If your property abuts a chaparral canyon in Scripps Ranch or Rancho Peñasquitos, the urban-wildland interface rules govern siding, vents, and sometimes roof assemblies. Missing those details in the plans means a failed final inspection and another month of delay.
- Coastal moisture and marine-layer exposure. Homes west of I-5 in Ocean Beach or Point Loma deal with persistent damp air. Proper flashing, vapor barriers, and vented assemblies matter more here than in inland communities, and cutting those corners leads to mold and framing rot within a few years.
Pricing for ADU Builders in San Diego, CA
Here are honest ranges for San Diego, as of 2025 – 2026. A prefab studio or one-bedroom ADU lands between $140,000 and $280,000, including site work, utilities, and permits. A custom one-bedroom detached ADU runs $180,000 to $350,000. Two-bedroom custom detached units typically run $300,000 to $420,000, especially on hillside lots with geotech and retaining work. Garage conversions on flat San Diego lots usually fall between $120,000 and $200,000, but that assumes the existing structure is in sound shape. A JADU inside an existing home runs $80,000 to $150,000. Every estimate we write in San Diego includes line items for permits, fees, and contingency allowances. Call (619) 376-2760 for a free estimate, and we’ll put your number in writing before any commitment.
We Also Serve Cities Near San Diego
Our San Diego office regularly sends crews to Coronado, National City, Chula Vista, and Lemon Grove. Each of those cities runs on its own building department and its own ADU review process. If you’re just outside San Diego proper, call (619) 376-2760 and we’ll tell you whether your address falls in our normal service area. For everything else in the region, see ADU Builders in San Diego to learn more.
Serving San Diego, CA - Our Local Coverage Area
We’re based in the San Diego area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU Builders in San Diego
The 2020 program lets you build two ADUs on single-family lots when you include at least one JADU, effectively tripling the housing units allowed on a standard San Diego parcel. On a 5,000 sq ft lot, that usually means a detached one-bedroom ADU plus a JADU carved out of the existing home or garage. Parking requirements are waived for the second unit in most zones. Call (619) 376-2760 and we’ll walk through what your specific lot qualifies for under current San Diego code, because bonus-program rules shift by overlay zone and hillside designation.
You can add an ADU, but San Diego will not issue a building permit for new construction while a known unpermitted conversion sits on the same parcel. The city requires you to either legalize the existing conversion, which means bringing it up to current code for electrical, plumbing, and egress, or demolish it and start fresh. We handle both paths: some North Park homeowners legalize the old garage unit and then add a detached ADU behind it; others scrape it entirely and build one larger permitted unit. The cost difference is real, so we price both scenarios before you decide. Call (619) 376-2760 to have us look up your parcel history.
Generally yes, provided your lot falls under the coastal ADU height provisions San Diego adopted after 2020, and as long as the structure still meets rear and side setback rules for your specific zone. Point Loma’s older hillside subdivisions often carry additional geotech requirements that can influence foundation design and usable square footage. The answer depends on your lot’s LDR (land development review) status and whether your home sits in a coastal overlay. We’d rather look at your specific parcel than give you a blanket yes. Call (619) 376-2760 for a site-specific read.
Expect the city to require you to bring the touched portions of the existing home up to current code for electrical, plumbing, and smoke/CO detection. A 1970s Clairemont home often has aluminum branch wiring, a 100-amp panel, and cast-iron drain lines. When you tie an ADU into those systems, the inspector will typically require a panel upgrade to 200 amps, replacement of the portions of wiring you touched, and sometimes a full sewer lateral replacement if the existing line runs under the new addition. We write these upgrades into your estimate as line items, not surprises. You’ll know the total before demolition starts.
San Diego measures setbacks from the property line, not from the slope, but canyon-lot ADUs often trigger a geological review that effectively changes what you can build and where. If the only buildable flat area sits between the house and a descending slope, the setback from that slope edge is commonly determined by soils engineering and the city’s hillside review process, which may require retaining walls, deepened footings, or pier-supported foundations. That’s exactly the kind of project the 2020 bonus program was meant to encourage, but the engineering costs are real. On a Clairemont canyon lot, our crew once opened up a 1960s-era garage conversion to find the original footing was just a 4-inch unreinforced slab poured directly on uncompacted fill, no rebar, no stem wall, and a previous owner had cut a doorway through the rear bearing wall without a header. We stopped work, brought in our soils engineer, and redesigned the foundation with a deepened perimeter footing and helical piers. The homeowner approved the change order in writing before we dug a single hole, and the new ADU now carries a fully permitted structural upgrade instead of a hidden collapse risk. Call (619) 376-2760 if you have a canyon lot and want to know what’s actually buildable.
If you’re still in the planning stage, the fastest way to get real numbers is a site visit. Call (619) 376-2760 or ask us to come out and walk the property. We’ll measure, check the slope, run a preliminary buildability read, and write you a price in plain English. No pressure, no deposit required for the first conversation.
Written by Russ Delmar, Owner at Lodgewick ADU San Diego, serving San Diego and surrounding communities.
