ADU design-build · San Diego County
San Diego ADUs
Detached, attached, garage conversions and junior ADUs, designed and built for your lot.
BHI Builders designs, permits and builds detached ADUs, attached ADUs, garage conversions and junior ADUs across San Diego County's 19 permit authorities, as one team, under California contractor license 738313, issued in 1997.
- 1997Licensed in California sinceCheck the license
- 111Permits on the public record, 2000 to 2025See the projects
- 5.0Google rating from 17 reviewsRead the reviews
- A+Better Business Bureau ratingSee the BBB profile
Your land. A second home.
An ADU can house a parent, give a grown child a start, earn rent, or let you move in while you rent the main house. We take it from the first look at your lot to the final inspection, in La Jolla, Del Mar, Encinitas, Carlsbad and across San Diego County.
Four ways to add a home
01 / Detached
Detached ADU
A separate home in the yard, one or two stories. The most privacy and the strongest rental.
The wrong choice when the yard is small or steep: a new foundation and new utility runs are most of the work.
About this type02 / Attached
Attached ADU
Built onto the side or back of your house, with its own entrance. Sharing a wall saves on foundation and utility runs.
The wrong choice when the only place it fits is the front setback or over the house's main drain.
About this type03 / Garage
Garage conversion
Your garage becomes a full home. Usually the fastest path, because the slab, walls and roof are already there.
The wrong choice when the slab is cracked or too low, or the garage sits in the City's Beach Impact Area, where its parking must be replaced.
About this type04 / Junior
Junior ADU
Up to 500 square feet carved out of your house, with its own entrance and an efficiency kitchen. Ideal for a parent or a caregiver.
The wrong choice when you want to rent it and live elsewhere: a junior ADU that shares a bathroom needs the owner on the property.
About this type
On the call we tell you which one fits your lot, including if the answer is none.
How an ADU comes together
- 01Site and layout.. We mark the footprint and find the sewer, water and power lines it will tie into.
- 02Foundation.. Trenches, rebar and the plumbing under the slab are inspected, then the concrete is poured.
- 03Framing.. Walls, then the roof structure, then sheathing that makes the shape solid.
- 04Systems.. Plumbing, wiring and ducts run through the open walls before they're insulated.
- 05Weather-tight.. Windows, roofing and the weather barrier close it in.
- 06Finishes.. Drywall, cabinets, tile, floors and fixtures. Final inspection, then the keys.
What moves the price.
$82,560 to $428,632
Plain-spec planning range across the four types today. Your size, site and finishes move it.
How much does an ADU cost in San Diego County?
| Type | Plain spec | Low | High |
|---|---|---|---|
| Detached ADU | 800 sq ft | $318,040 | $428,632 |
| Attached ADU | 600 sq ft | $244,301 | $331,021 |
| Garage conversion | 450 sq ft | $95,862 | $131,732 |
| Junior ADU | 400 sq ft | $82,560 | $112,734 |
BHI's range model, October 2026. Planning ranges at a plain spec, not a quote for your lot.
- Size. The biggest lever. Every room adds framing, finishes and fees.
- Your site. Slope, tight access and distance to the sewer line add excavation and labor.
- Utilities. A new sewer lateral or a bigger electrical panel can add five figures. We check both on the first visit.
- Finishes. Cabinets, tile, windows and fixtures can move the total more than the floor plan does.
- Fees. State law waives impact fees on ADUs under 750 square feet. Larger units pay a share of the main house's.
About a year, start to finish.
- Design and engineering
- 1 to 3 months
- City review and permits
- 2 to 6 months
- Construction
- 4 to 8 months
Garage conversions and junior ADUs move faster. A preapproved plan can shorten City review to about 30 days.
From our own permit record
BHI's two most recent County ADUs each spent about seven months in plan review. The solar ADU's plans went to the County in January 2025 and its permit issued in August 2025; the two-story ADU's went in November 2023 and issued in July 2024. State law gives a city or county 60 days to decide a complete ADU application, and 15 business days to say whether it is complete.
Step inside
Light from two sides, a kitchen that fits real cooking, and a bedroom that feels like its own place. This is what 800 square feet can be.
Four steps, one team.
Visit. We walk the lot with you and check what the rules and utilities allow.
Design. Plans drawn around your lot and the way you will use the ADU.
Permits. We prepare the submittal and answer the City's corrections.
Build. One crew from foundation to final inspection.
Where we build ADUs
A permit in Escondido runs through the City; in Rancho Santa Fe or Hidden Meadows it runs through the County of San Diego. We submit to all 19 offices in the county.
All 19 permit authorities: San Diego, Carlsbad, Chula Vista, Coronado, Del Mar, El Cajon, Encinitas, Escondido, Imperial Beach, La Mesa, Lemon Grove, National City, Oceanside, Poway, San Marcos, Santee, Solana Beach, Vista, Unincorporated San Diego County.
ADUs we've built.
Hillside ADU
Two-story ADU
ADU
Hillside ADU
ADU
Three of them, from the record
- Two-story ADU and a junior ADU1,152 sq ft detached ADU with a deck and garage, plus a 498 sq ft junior ADU · North County Metro, near Escondido · County permits issued July 2024, completed 2024
- Two detached ADUs and a garage conversionTwo 940 sq ft detached ADUs and a 320 sq ft garage conversion · Escondido · City of Escondido permits issued June 2025
- ADU with rooftop solarSingle-story, L-shaped, solar on both wings · Hidden Meadows, near Escondido · County plans submitted January 2025, permit issued August 2025
BHI Builders’ work is truly incredible! I had such a great experience working with this company and would highly recommend them for any construction project. Their communication was excellent throughout the entire process, and every member of the team was professional, friendly, and a pleasure to work with. I couldn’t be happier with the results!
Nila Makhfi, on Google
Questions homeowners ask
How much does an ADU cost in San Diego?
At a plain spec, our calculator puts a detached ADU of about 800 square feet at $318,040 to $428,632. A garage conversion starts near $95,862. Your site, utilities and finishes decide where you land.
How big can an ADU be?
In the City of San Diego, detached and attached ADUs can be up to 1,200 square feet. A junior ADU is up to 500 square feet inside the house. A garage conversion keeps the garage's existing footprint.
How long does it take?
Most detached ADUs take about a year from the first drawings to move-in: a few months of design, a few months of City review, and four to eight months of construction. Conversions are faster.
Do I have to replace the parking I lose?
Usually not. The City doesn't require replacement parking when you convert a garage, except in the Beach Impact Area. State law also waives ADU parking near transit.
Can I rent it out?
Yes, for stays of 30 days or longer. Short-term vacation rentals aren't allowed in ADUs in the City of San Diego.
Do I have to live on the property?
Not for an ADU. For a junior ADU, the owner must live on the property unless the junior ADU has its own bathroom.
Will an ADU raise my property taxes?
Only for the value the ADU adds. Your main house keeps its current assessed value.
Can I sell the ADU separately?
In the City of San Diego, sometimes: the City allows ADUs to be sold as condominiums under state law, with conditions. Most owners keep it.
Do you build garage conversions, attached and junior ADUs, or only detached?
All four. BHI builds detached ADUs, attached ADUs, garage conversions and junior ADUs, and the permit record shows each kind. Which one fits your lot is the first thing we settle on the call.
How do I check an ADU contractor's license in San Diego County?
Look the number up on the Contractors State License Board's site, where you can see the classification, the bond, the workers' compensation and any disclosed complaints. BHI's number is 738313, a B General Building license issued in 1997, and the same number is on every page of this site.
Is my lot a fit?
Most single-family lots in San Diego can take one ADU and one junior ADU. Slope, easements, fire zones and the coastal zone can change what fits. We check all of them on the first visit.
Tell us about your lot.
We'll walk it with you and tell you what fits.
Rules current as of October 2026, from the City of San Diego and California HCD.
