Know Your ADU Budget Before You Meet a Contractor in Redwood City
San Mateo County permit fees and utility connection costs are included — not hidden in a footnote.
What an ADU Actually Costs to Build in San Mateo County
ADU construction cost in Redwood City is not a single number — it's a range shaped by five specific variables.
ADU construction cost — the total investment required to design, permit, and build an accessory dwelling unit — varies widely depending on construction type, unit size, site conditions, permit fees, and utility connection requirements. A studio-sized JADU conversion and a two-bedroom detached new build are both ADUs on paper. They are not the same product, and they do not cost the same amount.
Any figure published without those variables attached is a statewide average applied to a project that hasn't been defined yet. The ranges on this page are illustrative; the only number that matters is the one built from your actual parcel.
Design, permits, construction & final sign-off — one licensed contractor, CA #1119304.
Why ADU Cost Varies So Much Across San Mateo County
San Mateo County contains 20 incorporated cities — and each one runs its own permit fee schedule. ADU permit fees (the charges for plan check, permit issuance, and separate electrical, plumbing, and mechanical permits) are calculated differently in Redwood City, San Mateo, Foster City, and unincorporated county land. Two identical garage conversions on adjacent parcels in different jurisdictions can carry a $3,000 to $8,000 difference in permit costs alone.
The permit line item is just one piece. Utility connection fees — charges from water, sewer, and gas districts for connecting a new unit into existing service — can add $10,000 to $30,000 or more depending on whether the ADU shares a meter with the primary residence or requires a separate connection. Shared-meter units avoid most of those fees; separately metered units trigger them in full.
How a Redwood City Homeowner's ADU Budget Actually Came Together
A homeowner came to us with a garage conversion in mind and a ballpark from a web search: roughly $80,000 to $150,000 for a garage ADU in California. That range isn't wrong — it just isn't a project estimate.
When we reviewed the specific parcel — a detached two-car garage in Farm Hill, built in the 1970s — a few things came into focus. The slab sloped moderately toward the rear, requiring a sub-slab leveling layer before flooring. The existing 100-amp service needed an upgrade to support the ADU's circuits. And the homeowner wanted a separate meter for rental, which triggered a San Mateo County Water Agency connection fee of roughly $14,000. None of those items are unusual — all of them are invisible in a statewide range. The final budget landed inside the published range, the homeowner knew exactly why, and there were no surprises after the estimate.
How Bark and Build Builds Your Estimate From the Ground Up
Every estimate starts with your specific parcel — not a published range. Construction type, lot conditions, jurisdiction, utility connection requirements, and design scope all feed into the number before it's presented.
We manage permit applications and utility coordination as part of the ADU scope, so the permit fee schedule for your specific city is already in the estimate. The utility connection cost — shared-meter or separately metered — is already in the estimate. The soft costs — architectural, engineering, and Title 24 documentation fees that typically run 10 to 20 percent of total project cost — are already in the estimate. You get one number with a clear breakdown, and CA License #1119304 covers every phase from design to final inspection. One licensed contractor, no handoffs between phases.
The Two Cost Categories Every ADU Budget Is Built From
Every ADU project cost breaks into two categories — both matter, and both are itemized in every estimate.
Direct Construction Expenses
These vary most by construction type. A ground-up detached ADU carries the full scope; a garage conversion reuses the shell but still needs full MEP, Title 24 envelope upgrades, and often structural work on the existing slab or framing.
- Foundation (slab, raised, or modified by ADU type)
- Framing — new, or structural modification of existing
- MEP — mechanical, electrical, plumbing rough-in and finish
- Insulation, drywall, roofing, and exterior envelope
- Interior finishes — flooring, tile, cabinetry, fixtures
Non-Construction Expenses
Typically 10 to 20 percent of total project value in San Mateo County. They're the documentation and approvals that make the build permittable — and they're easy to overlook in a per-square-foot estimate.
- Architectural and design fees
- Structural engineering
- Title 24 energy calculations
- Soil testing where required
- Survey work and permit application fees
The Five Variables That Determine Your ADU Build Price
Five factors determine ADU construction cost in Redwood City — each one shifts the number in a different direction.
ADU Projects Across Redwood City & San Mateo County
We serve homeowners throughout San Mateo County — every incorporated city and unincorporated county land. Permit fee schedules and utility connection costs are tracked by jurisdiction, so your estimate reflects your city, not a county average.
Cost ranges on this page are illustrative and intended for general budgeting only. Your project-specific estimate is built from your actual parcel, construction type, jurisdiction, and utility configuration.
Request a Project-Specific ADU Cost Estimate
The most useful number we can give you is the one tied to your actual parcel. Share your address, your ADU type, and any site conditions you're aware of, and we'll build a cost breakdown from your construction type, lot conditions, permit jurisdiction, and utility connection requirements — so you walk into any planning conversation knowing exactly what the project involves.