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Huntington Park
One of San Bruno’s first post-war suburbs. Flat lots, compact homes, close to BART. Straightforward garage conversions and rear-yard ADUs.
San Bruno ADU Specialists — CSLB #1041528
ADU Construction in San Bruno — Flatland & Hillside Lots
Garage conversions, detached units, and lower-level conversions in Huntington Park, Crestmoor, Rollingwood, and beyond. Design, permit, and build by a contractor with hillside expertise.
Two Landscapes, Two Opportunities
San Bruno divides into flatlands and hillsides.
San Bruno’s residential neighborhoods fall into two distinct categories: flatland post-war suburbs and hillside raised-ranch communities. Huntington Park, San Bruno Park, and Lomita Park sit on flat terrain — one of San Bruno’s first suburban developments, built in the late 1940s and early 1950s with compact homes on modest lots. The hillside neighborhoods — Crestmoor, Rollingwood, Mills Park, Monte Verde, and Portola Highlands — feature larger mid-century homes on sloped terrain, many with lower levels that face the street at grade.
This terrain divide shapes ADU opportunities. A flatland lot in Huntington Park presents straightforward garage conversions and small detached units. A hillside lot in Crestmoor or Rollingwood opens the possibility of converting an existing lower-level space or building a detached unit that uses the slope for natural separation and privacy.
ACI builds on both terrain types throughout the Bay Area. Our crew handles flatland foundation work, hillside retaining walls, raised-ranch lower-level conversions, and the full range of ADU construction. We manage design, permitting, structural engineering, and construction under one contract.
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Terrain Agnostic
We build on flatland and hillside lots. One crew, one contract, one expertise.
ADU Strategies by Lot Type
San Bruno’s ADU Opportunities
Huntington Park · San Bruno Park · Lomita Park
Flatland Lots
Huntington Park is one of San Bruno’s first suburban neighborhoods, developed in the late 1940s and early 1950s. San Bruno Park and Lomita Park are similar vintage. The homes here are compact — typically 900 to 1,200 square feet, single-story, on lots of 4,000 to 5,500 square feet. Many have detached single-car garages accessed from the rear or side of the lot.
Garage conversion: The most cost-effective ADU path in these neighborhoods. The existing garage provides the shell. The conversion involves building habitable walls within that shell, insulating, adding a bathroom and kitchenette, installing independent electrical and plumbing, and replacing the garage door with a wall and entry.
Detached rear-yard unit: Work on lots where the rear yard has enough depth — typically 25+ feet of usable space after the 4-foot setback. The flatland lots are generally easier to build on: no retaining walls, no graded foundations, no slope drainage engineering.
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Flatland lots in San Bruno’s first post-war suburbs offer straightforward, cost-effective ADU opportunities. This is among the most practical path to an ADU on the Peninsula.
Crestmoor · Rollingwood · Mills Park · Portola Highlands
Hillside Lots
Crestmoor was developed in the early 1950s on former ranch land west of I-280. The homes are California mid-century — raised ranches and split-levels built between 1950 and 1970, with curving streets that follow the hillside contours. The lots are larger than the flatland neighborhoods, many exceeding 6,000 square feet, with rear yards that slope with the terrain.
Crestmoor’s larger lots and hillside terrain create natural separation between the main house and a potential ADU site. A detached unit can sit at a different elevation, using the slope to provide privacy and a separate entrance. Many Crestmoor raised ranches have a garage and unfinished or semi-finished lower level at street grade, with the main living space above. Converting this lower-level space into an ADU takes advantage of the existing structure, though moisture management, fire-rated separation, and adequate natural light require careful design.
Rollingwood, Mills Park, Monte Verde, and Portola Highlands feature similar mid-century raised-ranch construction on hillside terrain. These neighborhoods offer both detached rear-yard unit opportunities (on larger lots) and lower-level conversion possibilities within existing homes.
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Hillside raised-ranch homes offer ADU opportunities within existing structure or in rear-yard space. Moisture management and fire-rated assemblies are critical.
Permitting
Permitting in San Bruno
San Bruno processes ADU permits through its Community Development Department and Building Division. Like all California cities, San Bruno must approve compliant ADU applications ministerially — no discretionary review, no public hearing. State law requires action on a complete ADU application within 60 days.
Online Portal
San Bruno requires applications through the MGO Connect online portal. Plan review does not commence until plan review fees are paid. We manage this administrative coordination as part of our design-build scope.
Pre-Approved Plans
San Bruno has launched a pre-approved ADU program under AB 1332. Pre-approved plans can be used as-is or as a starting point for customization, speeding up the permitting process.
FAR Standard
San Bruno uses FAR as a development standard for ADUs. On smaller flatland lots, this may limit the ADU to something smaller than the state-maximum 1,200 square feet. We calculate allowable ADU size during feasibility assessment.
Individual Metering
Each ADU must be individually metered for gas and electric service under California Public Utilities Code Section 780.5. This means coordinating with PG&E for separate meter installation — a step with its own timeline that should be initiated early.
60-Day Timeline
State law requires action on a complete ADU application within 60 days. Completeness of the initial submission is critical. We submit thorough plans that anticipate plan check issues and keep your project on track.
Design-Build Advantage
We manage the full permitting process from initial design through final approval. We submit through San Bruno’s online portal, respond to plan check comments, and coordinate with the Building Division.
County resources: San Mateo County ADU Resource Center provides regional resources, pre-reviewed designs, and guidance on the permitting process.
Neighborhoods
San Bruno Neighborhoods Where We Build
- 📍San Bruno Park
Mid-century flatland neighborhood. Homes similar to San Francisco’s Sunset district — small, single-story, densely spaced. ADU opportunities depend on lot depth.
- 📍Downtown & Tanforan
Mixed-era neighborhood near downtown. Older housing stock (1920s–1950s). Charming homes that may need infrastructure upgrades as part of the ADU project. Transit-oriented.
- 📍Crestmoor
Mid-century hillside neighborhood. Raised ranches and split-levels on curving streets. Larger lots. Partially rebuilt after the 2010 PG&E pipeline incident. Modern homes share streets with vintage ones.
- 📍Rollingwood
1950s–1960s raised ranches on hillside terrain with bay views. Steep streets. Larger homes (1,100–1,500+ sf). Strong candidate for lower-level conversions.
- 📍Mills Park & Monte Verde
Post-war neighborhood bridging flatlands and foothills. Classic mid-century homes. Mixed terrain — some lots flat, some sloped.
- 📍Portola Highlands
Exclusively residential. Mid-century one- and two-story homes. San Bruno’s largest homes (2,000+ sf). Near Sweeney Ridge open space. Hillside lots with larger footprints.
- ☎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 San Bruno
San Bruno construction costs track with the broader Peninsula market. Hillside site work on sloped lots in Crestmoor or Rollingwood adds meaningfully to the budget compared to flatland conversions in Huntington Park.
*All ranges reflect Peninsula market conditions — varies by scope, site conditions, and finish level
Garage Conversion
Any neighborhood; lowest cost entry point
$150K – $250K+Lower-Level Conversion
Shell exists, but moisture remediation, fire-rated separation, and potential modifications increase scope.
$180K – $300K+Detached ADU — Flat Lot
Rear-yard new construction. Standard foundation, framing, utilities, finishes.
$275K – $400K+Detached ADU — Hillside Lot
Retaining walls, engineered foundation, grading, slope drainage, complex utility routing.
$300K – $450K+JADU (Accessory Dwelling Unit in Main Home)
500 sq ft or less. Converting existing interior space with 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 San Bruno 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 San BrunoHomeowners Choose ACI
We handle both terrains
Our crew works on flat lots in Pacifica and Daly City and on hillside lots throughout the northern Peninsula. San Bruno’s flatland-to-hillside divide doesn’t require two different contractors — it requires one crew that handles both.
Lower-level conversions are our expertise
Fire-rated assemblies, moisture management, potential slab modification, and window additions through foundation walls. This is general contractor work — structural work that our crew does directly, not as a specialty.
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