A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateTrusted ADU Builders for San Diego Homeowners
Adding a second home to your San Diego lot should not mean living through months of dust, noise, and surprise invoices. Seedling ADU San Diego builds accessory dwelling units, garage conversions, and home additions with a written price before any work starts and a 365-Day Done Right Promise that covers every job we complete. Led by Ben Ortega, our crews show up background-checked and uniformed, with shoe covers and drop cloths on every visit. We work with families in North Park, Clairemont, Rancho Bernardo, and across San Diego County who want a new home on their lot without turning their existing home into a construction zone. For homeowners specifically in the city, our ADU Builders - San Diego team delivers the same fixed-price, clean-site experience. Call (858) 988-6447 for a free estimate and a straight answer about what your project will cost.
Key Takeaways
- Seedling ADU San Diego gives every family a written price before any work begins, with no surprise line items added later.
- Every ADU, garage conversion, and home addition is backed by the 365-Day Done Right Promise: if it is not done right, we make it right.
- The Cedarwell Care Promise means shoe covers, drop cloths, pet-safe products, and a clean-up photo before our crew leaves your property.
- We work with leading prefab and modular ADU brands including Boxabl, Plant Prefab, Tuff Shed, and James Hardie materials.
- A live person answers our phone 24/7 throughout your project. Call (858) 988-6447.
ADU Construction
ADU construction in San Diego is the full process of building a secondary dwelling on your existing residential lot, from the first site survey through framing, utilities, drywall, flooring, and final inspection. That process is where most families feel the most uncertainty, since budgets shift, timelines stretch, and communication stops once the crew arrives. Seedling ADU San Diego runs construction differently: you receive a fixed written price before tools leave the truck, and every day ends with a photo of the clean-up sent to your phone so you know exactly what the crew left behind. Most San Diego ADU construction projects run $180,000 to $320,000 depending on square footage, site access, and finish level, and we walk you through that range before you commit to anything.
Site Preparation
San Diego lots bring their own set of conditions: sloping grades in Mission Hills, tight side yards in North Park, and utility easements that vary block by block. For homeowners in the South Bay, National City ADU Builders from Seedling handle these same grading and drainage challenges every day. We handle grading, drainage, and utility trenching before framing begins so the foundation work doesn’t fight the terrain.
Permits and Inspections
Ben Ortega and the team manage the full permit path with the City of San Diego and County of San Diego, depending on your parcel. Every inspection point is scheduled, attended, and documented so there are no surprises when the inspector walks the site.
Detached ADU
A detached ADU is a standalone secondary home built in your backyard, fully separated from the main house, with its own entrance, kitchen, bath, and utilities. It’s the right choice for San Diego homeowners whose lot has the side or rear yard space for a new structure 400 to 1,200 square feet, and who want a clear boundary between the main home and the rental or family unit. Seedling ADU San Diego has built detached ADUs in neighborhoods like Mira Mesa, Otay Mesa, and La Jolla, with written pricing that locks before excavation starts. A detached ADU in San Diego typically ranges from $200,000 to $400,000, shaped by square footage, foundation type, and whether you choose a panelized system, a prefab unit, or true site-built construction.
Foundation Choices That Fit Your Lot
Some San Diego backyards work beautifully with a slab-on-grade foundation, while hillside lots in areas like Rancho Peñasquitos need pier-and-grade-beam engineering. We assess soil and slope during the estimate visit and price the right foundation the first time.
Prefab and Panelized Options
When a family chooses a Plant Prefab or Boxabl unit, we handle site prep, utility connections, and finish work around the factory-built shell. For James Hardie siding and trim, we coordinate material lead times so your project doesn’t stall waiting for product.
JADU
A JADU, or Junior Accessory Dwelling Unit, is a smaller second unit created within the walls of an existing single-family home, capped at 500 square feet and typically built as a garage conversion, basement conversion, or spare-room transformation with its own entrance and efficiency kitchen. San Diego homeowners choose a JADU when they want rental income or a private space for aging parents without the cost of a fully detached structure. Seedling ADU San Diego handles JADU design, permits, and construction, including the separate entrance, kitchenette, and bathroom requirements that San Diego code enforces. JADU projects in San Diego generally run $80,000 to $150,000, with the final number driven by existing plumbing locations, electrical panel capacity, and the condition of the space being converted.
Garage-Space Conversions
A garage JADU is one of the smartest uses of under-used square footage in older San Diego neighborhoods like Normal Heights and City Heights. For properties near the peninsula, our ADU Builders in Coronado handle garage conversions with the same clean, code-compliant approach. We keep the conversion clean: drywall, insulation, a proper entry door, and the kitchenette and bath the code requires.
Interior Living Conversions
Sometimes the best JADU candidate is a large recreation room or an attached studio with a private exterior door. We frame the separation wall, install the efficiency kitchen, and make sure the new unit has its own heating and cooling so the main house’s comfort isn’t compromised.
ADU Plans
ADU plans are the architectural drawings, structural calculations, and permit documents that the City of San Diego or County of San Diego must approve before any ADU construction begins. They include site plans, floor plans, elevations, electrical and plumbing layouts, and title-24 energy calculations, and they’re where a project either gets approved in weeks or stalls for months. Seedling ADU San Diego produces or coordinates ADU plans for every project, working with structural engineers and energy consultants who know exactly what San Diego plan reviewers look for. Plan costs typically run $5,000 to $12,000 depending on the ADU type and site complexity, and we include plan preparation in our written project price when you build with us.
Site-Specific Drawings
A plan set for a flat lot in Bonita looks very different from one for a hillside parcel in La Mesa. We measure, survey, and draw for your actual lot, not a template, so the permit submittal moves without redlines.
Structural and Title 24 Coordination
We bring in licensed structural engineers and Title 24 energy consultants on every project. Their calculations are folded into the plan set before submittal, so the building department sees a complete package the first time.
ADU Contractor
An ADU contractor is the licensed professional who manages the entire accessory dwelling unit build, including permits, subcontractors, scheduling, materials, and inspections. The difference between a good ADU contractor and a difficult experience is how clearly the price is set and how well the crew communicates once work starts. Seedling ADU San Diego is led by Ben Ortega, who sets a written price before the first trade shows up, and who holds every crew member to the Cedarwell Care Promise on every job site. Our contracting work for a San Diego ADU, garage conversion, or addition typically runs $160,000 to $350,000 depending on scope, and that figure includes all labor, materials, permits, and the 365-Day Done Right Promise in writing.
One Point of Contact
You will not be juggling calls from foundation crews, electricians, and drywall finishers. Ben and the project team coordinate every trade and give you one phone number to call, answered by a live person, 24/7.
Trade Coordination and Scheduling
San Diego’s best subcontractors book out weeks in advance. We schedule them in the right order, confirm lead times on windows and doors, and keep the project moving through inspection milestones without you chasing anyone down.
ADU Design
ADU design is the architectural and interior planning process that determines how your new unit looks, functions, and connects to your existing home and property. Good ADU design considers rooflines, window placement for San Diego’s light, privacy between the main house and the unit, and floor plans that make a 500-square-foot home feel livable rather than cramped. Seedling ADU San Diego starts every design conversation with your lot, your goals, and your budget, then shows you options across multiple formats and materials. Design fees in San Diego typically run $3,000 to $8,000 for the design phase, which we credit back toward construction when you build with us.
Plan Options Across Price Points
We can design a custom backyard ADU, adapt a factory plan from a brand like Boxabl or Plant Prefab, or convert an existing garage using a JADU layout. Each option gets priced against the others so you can choose with real numbers, not guesses.
Material and Finish Selections
James Hardie siding, composite decking, and interior finishes are selected during design so they’re ordered early and on-site when needed. No waiting on a backordered tile or window because the selections were a last-minute scramble.
Backyard ADU
A backyard ADU is a detached secondary home placed in the rear yard of your San Diego property, designed to maximize the usable outdoor space you have while giving the new unit privacy and its own access path from the street or alley. Backyard ADUs are the most common type of ADU construction in San Diego because our lots, especially in neighborhoods like Spring Valley, Lemon Grove, and Casa de Oro-Mount Helix, often have generous rear yards that are otherwise underused. Homeowners looking south of the city can rely on ADU Builders in Chula Vista for the same backyard ADU expertise. Seedling ADU San Diego builds backyard ADUs from 400 to 1,200 square feet with one-bedroom, two-bedroom, and studio layouts. San Diego backyard ADU costs typically run $200,000 to $380,000, with the variance tied to square footage, site preparation, and whether the home is site-built or uses a prefab system.
Setbacks and Site Placement
Every San Diego neighborhood has its own setback rules for rear-yard structures, and some parcels carry easements that restrict where a new home can sit. We map your buildable area during the estimate and design for a placement that clears all restrictions.
Outdoor Connection
A backyard ADU should feel like it belongs on your lot, not like a box dropped behind a fence. We plan decks, entry paths, and landscape transitions so the new home connects to your yard and to the main house in a way that makes sense.
Brands We Service
We work directly with Boxabl and Plant Prefab units, handling site preparation, foundation, utility connections, and finish work around their factory-built shells. Both brands require precise foundation tolerances and careful utility stubbing, and our crews have completed those pieces on projects across San Diego County. For exterior cladding and trim, we specify James Hardie siding and trim on most projects because of how it holds up against San Diego’s coastal moisture and inland heat cycles. We also coordinate Tuff Shed structures when a homeowner wants a finished, permitted studio built from a panelized or kit approach.
Whether you have a Boxabl unit on order, a Plant Prefab design selected, or a Tuff Shed shell already on site, we can take the project from bare dirt to final inspection. If you already own your ADU shell or have another brand selected, we’re glad to quote the site work and finish construction with the same written price and 365-Day Done Right Promise we apply to every project.
Signs You Need a Pro Right Now
- Your lot has drainage or slope issues. San Diego’s winter rains will find a poorly graded ADU site and put water against your new foundation. A proper site assessment catches drainage problems before concrete is poured.
- Your electrical panel is already at capacity. A new ADU adds circuits for kitchen, bath, and HVAC. If your existing panel can’t handle the load, you’ll need a subpanel or service upgrade planned into the project.
- You need a permit and you have not started drawings. The City of San Diego now requires complete plan sets for ADU permits, and incomplete submittals sit in review for weeks. A contractor who prepares plans correctly the first time saves you months.
- Your garage conversion has moisture or foundation cracking. Converting a garage in neighborhoods like Clairemont or Mira Mesa often reveals slab cracks and moisture intrusion. Addressing these before framing goes up prevents mold and structural problems later.
- You want certainty on price before you commit. If you’re comparing quotes that seem vague or open-ended, a written fixed price from a contractor who stands behind it with a 365-Day Done Right Promise is the clearest signal you’re working with the right team.
Our Process, Step by Step
- 1
On-site consultation and lot assessment. Ben Ortega or a project lead walks your San Diego property, measures the buildable area, checks setbacks and utility access, and listens to how you plan to use the new ADU. You’ll receive a written estimate covering the full scope, with no pressure and no obligation.
- 2
Written price and project agreement. Before any work starts, you get a fixed written price that covers labor, materials, permits, and subcontractors. No change orders appear mid-project unless you request a scope change in writing.
- 3
Design and permit submittal. Our design partners prepare site plans, structural calculations, and Title 24 reports for submittal to the City of San Diego or the County. We manage review comments and revisions until the permit is issued.
- 4
Construction with daily site care. Our background-checked, uniformed crews run the build with shoe covers and drop cloths inside your home, pet-safe products where there is a choice, and quiet-tool practices near bedrooms during school hours. A clean-up photo is sent before the crew leaves each day.
- 5
Final inspection and 365-Day Done Right Promise. We walk the finished ADU with you, complete the final inspection, and hand over the keys to a new home backed in writing. If anything is not done right within the first year, we make it right.
How Much Does ADU Builders Cost in San Diego?
A typical ADU build in San Diego runs between $180,000 and $380,000 depending on the type of unit, square footage, and site conditions. A JADU or garage conversion usually lands between $80,000 and $150,000, while a detached backyard ADU of 600 to 800 square feet typically costs $200,000 to $320,000. Larger two-bedroom units with premium finishes can reach $380,000 or more. The main variables are foundation type, utility trenching distance, panel upgrades, and the finish level you choose for kitchen, bath, and flooring.
What affects your price most is site preparation. San Diego lots with steep grades, retaining walls, or old sewer lines require more groundwork before framing begins. The second driver is finish level: quartz counters, custom cabinets, and James Hardie siding add cost compared to standard builder-grade materials. To avoid overpaying, insist on a written price that itemizes labor, materials, permits, and site work, and ask any contractor you interview whether their price includes all subcontractor work. Every Seedling ADU San Diego estimate includes the full written line-item scope, permits, materials, and the 365-Day Done Right Promise. Call (858) 988-6447 to schedule your free estimate.
Our Service Area Near San Diego
We build ADUs across San Diego and the surrounding cities, including ADU Builders in El Cajon, ADU Builders in National City, Spring Valley, Lemon Grove, Casa de Oro-Mount Helix, Bonita, Eucalyptus Hills, Bostonia, Coronado, La Mesa, and La Presa. Typical response time for an on-site estimate within San Diego County is two to three business days. For a closer look at how we approach ADU builds in the city, see our main ADU Builders in San Diego page or return to our home page for the full range of services.
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.
Frequently Asked Questions About ADU Builders in San Diego
An ADU builder is a licensed contractor who designs, permits, and constructs accessory dwelling units, garage conversions, and home additions on residential lots. Seedling ADU San Diego handles the full process from site assessment and plan preparation through final inspection and warranty. Call (858) 988-6447 to discuss your project and get a written estimate.
Most site-built ADU projects in San Diego take six to ten months from permit submittal to final inspection, while garage conversions and JADUs typically take three to five months. The timeline depends on plan-review speed at the City or County, utility connection scheduling, and material lead times. We give you a written schedule with your price so you know what to expect before work begins.
ADU costs in San Diego range from $80,000 for a JADU or garage conversion up to $400,000 for a large detached two-bedroom unit. Your specific number depends on square footage, site preparation, foundation type, finish level, and whether you choose a prefab or site-built approach. We provide a free, written, line-item estimate so you can plan without guesswork. Call (858) 988-6447 for exact pricing.
Yes, we handle site preparation, foundation work, utility connections, and finish construction for Boxabl and Plant Prefab units across San Diego County. We also work with Tuff Shed structures and specify James Hardie siding and trim on many projects. Bring us your brand preference, and we’ll price the full site and finish scope.
If something goes wrong after your ADU is complete, a live person answers our phone 24/7 and can dispatch a crew to assess the issue. The 365-Day Done Right Promise covers any work that was not done correctly during the first year, and we make it right at no charge. Call (858) 988-6447 any time.
If any part of your ADU, garage conversion, or home addition is not built correctly, Seedling ADU San Diego makes it right within the first year at no charge. The promise is provided in writing before work begins, not as a verbal assurance. It covers every project we complete, with no exceptions.
Clear a path from the street or alley to the build area, move pets to a safe part of the house during work hours, and let us know about any school schedules or quiet-time needs in your home. Our crews bring shoe covers, drop cloths, and pet-safe products on every visit. We’ll send a clean-up photo before the crew leaves each day, so you always know the condition of your property.
Schedule Your ADU Builders Service in San Diego Today
You deserve a written price before any work begins, a clean and respectful job site every day, and a finished ADU backed by the 365-Day Done Right Promise. Call (858) 988-6447 to schedule your free estimate with Seedling ADU San Diego. Ben Ortega and the team will walk your lot, answer your questions, and give you real numbers you can plan around.
Written by Ben Ortega, Owner at Seedling ADU San Diego, serving San Diego and surrounding communities.
