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Cost guide · San Mateo · City of San Mateo Community Development

San Mateo ADU cost guide — every line, no surprises

A fixed-price San Mateo ADU contract is the sum of five line items: base build, City of San Mateo Community Development permits and fees, design and engineering, sitework and utilities, and finishes. Below is how each one moves in San Mateo specifically — and where homeowners get burned by quotes that hide them.

City-specific deep dives

Base build — what $/sqft actually covers

Base build in San Mateo runs $385–$520 per square foot for a detached one-bedroom ADU at 2026 pricing. That number assumes Title 24 compliance, code-minimum insulation, mid-grade finishes, and standard MEP. Anything below $360/sqft in San Mateo is either skipping permits, skipping engineering, or carrying allowance line-items that will balloon during construction.

City of San Mateo Community Development fees & soft costs

San Mateo plan-check, school fees, sewer capacity, water meter, and utility connection fees typically land between $14,000 and $28,000. The variance is driven by lot conditions: a flat San Mateo lot on existing sewer is the low end; a hillside lot needing a new lateral and water tap is the high end. We pull these numbers at feasibility, not after deposit.

Design, engineering, and soils

Architectural design, structural engineering, Title 24 compliance, and (when San Mateo requires it) a geotechnical report typically run 8–11% of project cost. Hillside-zoned parcels and properties within special review overlays push this higher. We disclose the engineering scope up front so the design fee isn't a moving target.

Sitework, utilities, and the hidden 15%

Sitework in San Mateo — demolition, grading, retaining if needed, sewer tie-in, water service upgrade, electrical panel upgrade to 200A — is where most "cheap" quotes blow up. Older San Mateo homes nearly always need a panel upgrade and often a lateral upgrade. Budget 12–18% of project cost here. We scope this at survey, before contract.

Finishes — the only line you actually control

Finish allowances (cabinets, counters, flooring, fixtures, appliances) are the single line a San Mateo homeowner can move materially up or down. Going from builder-grade to mid-luxe adds roughly $35–$60 per square foot. Going to luxury finishes can add $90+/sqft. We model three finish tiers at design so the trade-off is visible, not buried.

San Mateo · Cost guide

Questions San Mateo homeowners ask about cost

Direct answers, San Mateo-specific.

  1. Are San Mateo ADU rents really that strong?
    Yes — Peninsula tenant demand from the biotech and tech corridors keeps 1BR ADU rents in the $2,800–$3,600 range.
  2. Do I need flood-elevation drawings?
    Only if your parcel sits in FEMA Zone AE or VE — mostly the eastern edge. We pull FEMA layers at feasibility.
  3. Does San Mateo have unique requirements that affect cost?
    Yes — City of San Mateo Community Development sets the local rules, and San Mateo has its own plan-check rhythm. The realistic numbers above reflect 2026 San Mateo conditions, not statewide averages.

Continue researching San Mateo

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