Garage Conversion
$150K – $250K+
The existing structure keeps costs lower. Includes foundation upgrades, insulation, full kitchen and bath, utility connections, and Title 24 compliance.
Fastest timeline
CSLB #1041528 — Family-Owned, Pacifica-Based
ADU Construction
on the Peninsula.
Designed, permitted, and built by one team. Add a fully permitted dwelling unit that generates $2,000–$3,000+ per month in rental income and increases your property value.
WHAT WE BUILD
Three Types of ADUs — and How to Know Which One Fits
Not every ADU is a backyard cottage. The right type depends on your lot, your budget, your goals, and what your property can physically support.
Detached ADU
A standalone structure built on your property, separate from the main house. It has its own entrance, utilities, and foundation. On the Peninsula, detached ADUs typically range from 400 to 1,200 square feet.
Best when:
- You have adequate yard space for a separate structure
- You want maximum privacy between main home and ADU
- You're building for long-term rental income or resale value
Under California law, detached ADUs up to 800 sq ft require only 4-foot setbacks, regardless of local zoning.
Attached ADU
Shares a wall with your existing home, reducing some structural costs while delivering a fully independent living unit. Popular for multigenerational families wanting proximity without giving up privacy.
Best when:
- Your lot is narrow or can't support a detached structure
- You're housing aging parents or adult children
- You want to minimize ground coverage and preserve yard space
- You're building within a tighter budget than detached allows
Attached ADUs up to 50% of the existing home’s sq ft are permitted by-right in most California jurisdictions under SB 9 and AB 2221.
Garage Conversion
Convert an existing attached or detached garage into a legal ADU. The existing structure keeps costs lower — foundation, roof, and walls are already there. Includes insulation, full kitchen and bath, utility connections, and Title 24.
Best when:
- You have an underutilized garage you're willing to convert
- You want the fastest timeline and lowest cost entry point
- Your lot doesn't have room for a new freestanding structure
- You need rental income sooner rather than later
When converting a garage, California law prohibits cities from requiring replacement parking spaces — even in areas with strict parking requirements.
California ADU Law
What the Law Means for Your Project
California has passed more than a dozen ADU-related bills since 2016. Here are the provisions that matter most for Peninsula homeowners.
No Owner-Occupancy Requirement
AB 976 made this permanent. You don't need to live on the property to build or rent an ADU.
Reduced Setbacks for Smaller ADUs
Detached ADUs up to 800 sq ft require only 4-foot side and rear setbacks — even if local zoning says otherwise.
60-Day Permit Approval
State law requires your city to approve or deny a complete ADU application within 60 days of submission.
No Replacement Parking
When you convert a garage, the city cannot require you to build replacement parking spaces anywhere on the lot.
Pre-Approved ADU Plans
AB 1332 required every California city to establish a pre-approved ADU plan program by January 2025, reducing design costs.
Separate Sale as a Condo
AB 1033 allows cities to permit the separate sale of an ADU as an individual condominium unit — independent of the main home.
Investment
What an ADU Costs on the Peninsula
We publish cost ranges because you should know what you're getting into before you call. The Bay Area runs 30–50% above the national average for construction.
All ranges reflect Peninsula market conditions — varies by scope, site conditions, and finish level
Detached ADU
$275K – $450K+Ground-up construction with its own foundation, utility connections, and full finishes. Hillside lots and larger units push costs higher.
Highest rental incomeAttached ADU
$200K – $350K+Shares a wall with your home, reducing some structural costs. Range depends on size, existing foundation condition, and finish level.
Ideal for multigenerational
The Investment Case
A studio or one-bedroom ADU can generate $2,000–$3,000/month in rental income. Property appraisers estimate an ADU increases home value by roughly 100× the monthly rent — a $2,500/month unit adds ~$250,000 in value.
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Faster home sale with ADU
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Typical value added
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Monthly rental income avg.
Our Process
From Your First Call to Certificate of Occupancy
One team handles everything — design, permitting, and construction under one contract.
Site Evaluation
We visit your property to assess grade, setbacks, access, utilities, and which ADU type is feasible. This evaluation is free.
Design & Engineering
Floor plans, elevations, structural engineering, geotechnical reports, and Title 24 calculations — all coordinated under one roof.
Permitting
We prepare and submit the complete permit application, respond to plan check comments, and track the 60-day approval clock.
Construction
Our crew handles foundation, framing, and structural work directly. We coordinate MEP subs and manage through finishes and landscaping.
Inspections & C of O
We schedule every required inspection and don't consider the project complete until you have your Certificate of Occupancy in hand.
Why ACI
Why Peninsula Homeowners Choose ACI
We do the structural work ourselves
Foundation, framing, retaining walls — our crew does this every day. We don't sub out the work that determines whether your ADU stands straight.
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.
We know hillside construction
Based in Pacifica — a city built on hills. Retaining walls, pier foundations, grading, and drainage aren't unusual add-ons. They're part of how we build.
Honest about what things cost
We publish cost ranges on this page. We'd rather have a real conversation about budget than win a project with a low-ball estimate that balloons in the field.
Family-owned, Pacifica-based
We live and work on the Peninsula. We're not a franchise dispatching crews from across the Bay — your project is local to us.
CSLB #1041528
Licensed GC — Class B
Bonded & Insured
Family-Owned
Service Area
Serving the San Francisco Peninsula
Based in Pacifica, ACI builds ADUs from San Francisco south to Redwood City — including the Coastside.
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Our home base — we know these hillside lots and planning department better than anyone.
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The largest ADU market on the Peninsula, with complex permitting and enormous demand.
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Hilly older neighborhoods and biotech-driven rental demand near the 101 corridor.
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Dense housing stock, smaller lots, and high demand for garage conversions and attached ADUs.
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- 📍Burlingame, Millbrae & More
Plus Brisbane, Colma, Half Moon Bay, and the Coastside. Contact us to discuss your project.