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Sunshine Gardens
Classic 1953–1957 post-war subdivision. Single-story ranch homes, flat to gentle slopes. BART accessible. Strong rental demand. One of the most straightforward neighborhoods for garage conversions and rear-yard detached ADUs.
South San Francisco ADU Specialists — CSLB #1041528
ADU Construction in South San Francisco — Design, Permit, Build
Garage conversions, detached units, and in-law spaces on post-war lots serving the biotech corridor. Design, permit, and build by a contractor who knows the housing stock.
South San Francisco Housing & ADU Opportunity
Post-war neighborhoods built for growth.
South San Francisco sits in a basin — San Bruno Mountain to the north, the Coast Range to the west, San Francisco Bay to the east. That geography shapes the city’s residential neighborhoods, which climb the hillsides on the western and northern edges while the flatlands along Highway 101 have become the world’s largest biotech cluster. Over 200 biotech and pharmaceutical companies operate in South City, anchored by Genentech, which was founded here in 1976.
The city’s residential neighborhoods — Sunshine Gardens, Serra Highlands, Westborough, Winston Manor, Sign Hill, Avalon — are predominantly post-war tract homes built between the late 1940s and the 1970s. These homes share the same mid-century construction characteristics found throughout the Peninsula: conventional wood framing, slab-on-grade or raised foundations, galvanized plumbing nearing the end of its service life, and electrical panels sized for a different era. The lots are modest. The demand for housing — rental housing especially — is intense.
ACI is a design-build general contractor based in Pacifica, adjacent to South San Francisco’s western border. We build ADUs throughout South City’s neighborhoods and know the construction characteristics of the post-war housing stock because it’s the same era and type we work on daily. We handle site assessment, design, structural engineering, permitting, and construction — including the structural work (foundation, framing, shear walls) with our own crew.
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Peninsula Expertise
Based in Pacifica. We know the post-war housing stock and hillside construction from Daly City to San Mateo.
ADU Types by Lot Type
South San Francisco’s ADU Opportunities
Sunshine Gardens · Serra Highlands · Winston Manor · Avalon
Flatland Tract Homes
The majority of South San Francisco’s single-family homes were built during the post-war construction boom of the late 1940s through the 1960s. Sunshine Gardens was developed between 1953 and 1957. Serra Highlands dates to the late 1950s. These neighborhoods share a common pattern: single-story ranch homes, typically 1,000 to 1,400 square feet on lots of 5,000 to 6,000 square feet, with attached or detached single-car garages.
Garage conversion: Like Daly City and Pacifica, these post-war homes have garages that are underused for parking and well-suited for conversion to studio or one-bedroom ADUs. The existing shell reduces construction cost. The conversion involves framing habitable walls, insulating, adding a bathroom and kitchenette, installing independent electrical and plumbing services, and replacing the garage door opening with a wall and entry.
Detached rear-yard unit: Many of these tract homes sit on lots with 30 to 40 feet of rear-yard depth behind the house. After the 4-foot rear setback, that’s enough space for a detached ADU of 400 to 800+ square feet depending on the lot width and the footprint available.
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The flatland lots are straightforward foundations, conventional framing, and standard utility connections. These are among the most cost-effective ADU projects.
Westborough · Sign Hill · Paradise Valley · Terrabay
Hillside Lots
South San Francisco’s western and northern neighborhoods sit on the slopes of San Bruno Mountain and the Coast Range foothills. Westborough, the city’s largest post-war development, was built on former dairy land in the 1960s through 1980s and features larger homes on hillside lots with curvilinear streets that follow the terrain.
ADU opportunities on hillside lots require more engineering but often yield more value. The sloped terrain creates natural separation between the main house and a detached ADU — the ADU can sit at a different elevation, tucked into the hillside with its own access. This also means retaining walls, stepped or engineered foundations, and drainage systems that account for the slope. ACI builds on hillside lots routinely — this is core work for our crew, not an exception.
Westborough’s larger lots (many exceeding 6,000 square feet) provide more rear-yard space for detached ADUs than the flatland tract neighborhoods. The trade-off is the hillside construction cost: retaining walls, foundation engineering, and grading add to the budget.
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Hillside lots often support larger, more valuable ADUs. Retaining walls, foundation engineering, and drainage design are our core expertise.
The Biotech Corridor Drives Rental Demand
Rental Market
South San Francisco’s biotech cluster isn’t a detail about the city’s economy — it’s the reason ADUs pencil out so well here. The roughly 200+ biotech companies east of Highway 101 employ thousands of workers — researchers, lab technicians, administrative staff, support personnel — many of whom need housing within a reasonable commute of their workplace. South San Francisco’s residential neighborhoods sit directly west of this employment center, separated by the freeway but connected by surface streets, shuttle routes, and short drives. An ADU in Sunshine Gardens or Serra Highlands is a 10-minute commute from the Oyster Point biotech campus. A detached unit in Westborough is 15 minutes from Genentech’s campus.
A one-bedroom ADU in South San Francisco can command $2,200 to $3,500+ per month depending on size, finishes, and proximity to transit. A well-built, modern ADU with its own entrance, full kitchen, and in-unit laundry competes not just with shared apartments but with the newer market-rate developments along the bayfront — at a fraction of those rents.
10-15 min
to Major Biotech Hubs
Permitting
ADU Permitting in South San Francisco
South San Francisco processes ADU permits through its Planning Division and Building Division. Unlike some Peninsula cities where a single building permit covers the ADU, South San Francisco requires both a Building Permit application and a Deed Restriction application. The deed restriction establishes that the ADU cannot be sold separately from the main home and must be rented for terms longer than 30 days. We coordinate both applications as part of our design-build scope.
60-Day Timeline
State law requires the city to act on a complete ADU application within 60 days. Completeness of the initial submission determines whether you hit that target or enter a cycle of plan check corrections. We submit thorough plans that anticipate common correction items.
HelloADU Program
South San Francisco offers a free program called HelloADU, administered by the nonprofit Hello Housing. Participating homeowners can receive up to 100 hours of free support in designing, constructing, and renting out an ADU.
Pre-Reviewed Designs
San Mateo County HEART has prepared detached ADU designs pre-reviewed by South San Francisco’s Building Division. These green, all-electric designs can reduce permitting time and design costs.
Deed Restriction
South San Francisco requires both a building permit and a deed restriction establishing that the ADU cannot be sold separately and must be rented long-term (30+ days).
Planning Meetings
Contact South San Francisco’s Planning Division at (650) 877-8535 or planning@ssf.net for ADU inquiries and to schedule a pre-application meeting before submitting formal plans.
Complete Application
We prepare and submit complete applications that anticipate plan check issues, reducing back-and-forth cycles and keeping your project on the 60-day timeline.
Design-build advantage: We handle the design-permitting-construction process under one contract. We coordinate both the building permit and deed restriction applications, manage the plan check process, and deliver the final certificate of occupancy.
Neighborhoods
South San Francisco Neighborhoods Where We Build
- 📍Serra Highlands
Late 1950s mid-century homes on quiet, wide streets west of El Camino Real. Near BART. Larger homes than some other post-war neighborhoods, typically 1,200 to 1,400 square feet.
- 📍Westborough
1960s–1980s homes on the western hillside. Larger lots, more rear-yard space, but hillside construction adds cost. Between I-280 and Skyline Boulevard. Higher home values.
- 📍Winston Manor
Post-war tract east of El Camino Real. Flat lots, close to BART and Kaiser medical offices. Practical lots for garage conversions and small detached ADUs.
- 📍Sign Hill
Mixed-era housing near the iconic hillside sign. Close to downtown Grand Avenue and the Oyster Point biotech hub. Hilly terrain in parts. Vintage homes with character.
- 📍Avalon & Buri Buri
Post-war neighborhoods west of El Camino Real. Quiet, family-oriented. Avalon features curving streets along the I-280 corridor. Near schools and parks.
- ☎Not Your Neighborhood?
Every lot is different. Call us at (650) 224-3052 and describe your property. We’ll tell you what’s typically feasible before you schedule a visit.
Investment
What an ADU Costs in South San Francisco
South San Francisco construction costs track with the broader Peninsula market. Hillside site work on sloped lots in Westborough or Sign Hill adds meaningfully to the budget compared to flatland conversions in Sunshine Gardens.
*All ranges reflect Peninsula market conditions — varies by scope, site conditions, and finish level
Garage Conversion
Existing structure, fastest timeline, lowest cost of entry
$150K – $250K+Detached ADU — Flat Lot
Sunshine Gardens, Winston Manor; standard foundation and site prep
$275K – $400K+Detached ADU — Hillside Lot
Westborough, Sign Hill; engineered retaining walls and pier foundations add cost
$300K – $450K+JADU (Accessory Dwelling Unit in Main Home)
Converting existing interior space with an efficiency kitchen
$100K – $200K+
The difference between flat-lot and hillside-lot detached ADUs is almost entirely foundation and site preparation. An engineered retaining wall on a South San Francisco hillside lot can add $20,000 to $80,000 depending on height, soil conditions, and equipment access. The San Mateo County ADU Resource Center estimates total ADU costs at roughly $450 to $600 per square foot including design, engineering, and permitting. For a realistic estimate based on your specific lot, call (650) 224-3052.
Why ACI
Why South San Francisco Homeowners Choose ACI
We know post-war construction
The housing stock in Sunshine Gardens, Serra Highlands, and Winston Manor is the same era and type we work on throughout Pacifica and the northern Peninsula. We know the framing, the plumbing, the electrical, and the foundations.
We handle hillside work
For the western neighborhoods — Westborough, portions of Sign Hill, Paradise Valley — our crew’s experience with hillside construction, retaining walls, and engineered foundations is directly relevant. This is core work for ACI, not a specialty we subcontract.
Structural work in-house
Foundation, framing, retaining walls — our crew handles the work that determines whether your ADU stands straight. We don’t sub that out.
One team, one contract
Design-build means you’re not juggling an architect, permit expeditor, and GC. One company, one contract, one person to call when anything comes up.
CSLB #1041528
Licensed GC — Class B
Bonded & Insured
Family-Owned