Published: 2 Nov 2026 · Last verified: 2 Nov 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
Two school districts tax the same 800 sq ft ADU in Campbell, and together they charge $5.40 per square foot — $4,320 total, the highest school-fee rate in this series. Campbell Union (K-8) takes $3.79; Campbell Union High takes $1.61. One parcel, two resolutions, one combined bill. Pasadena, by contrast, charges $2.24. The same ADU, the same state, a $2,528 school-fee gap drawn entirely by district boundaries.
Campbell sits in the heart of Silicon Valley, and its fee structure reads like it: valuation-based permits (the city’s cut scales with what you build), per-fixture-unit sewer math from a separate sanitation district, and a county-level pre-approved plan gallery instead of a city-run program. Our six-phase total lands at about $318,000, or roughly $398 per square foot — with the sewer line carrying the widest uncertainty in the series.
The short answer
| 800 sq ft detached ADU · Campbell · 2026 | Amount |
|---|---|
| Total build cost (see assumptions) | ~$318,000* |
| Cost per square foot | ~$398* |
| Highest line in the series | School fee, $4,320 |
| Widest uncertainty | Sewer, $0–$7,751 |
Phase 1 — Soft costs: the Campbell ledger
| Line item | Amount | Source / note |
|---|---|---|
| School fee — Campbell Union (K-8) | $3,032 | $3.79/sq ft × 800; campbellusd.org |
| School fee — Campbell Union High | $1,288 | $1.61/sq ft × 800; CUHSD 5/7/2026 approval |
| School fee combined | $4,320 | $5.40/sq ft — series high |
| Building permit + plan check | ~$3,529* | 2.00% of $100K valuation + 33% plan check + add-ons; FY 2026 schedule |
| Construction license tax | $400 | $0.50/sq ft × 800; Campbell Municipal Code 3.40 |
| Impact fees (3 types) | Proportional* | <750 exempt (§66311.5); 800 sq ft pro-rata; city rates unpublished |
| Sewer — WVSD connection | Up to $6,727* | $567.68/drainage fixture unit; FY 2024-25 rates |
| Sewer — WVSD capacity | Up to $1,024* | $86.42/fixture unit treatment capacity |
| Soft cost subtotal (verified portion) | ~$8,649* | Before sewer/DIF |
Phases 2–6 (construction) are carried from the series baseline at approximately $285,000; Campbell does not publish phase-level construction costs.
* Assumptions: $100,000 construction valuation for permit example (illustrative, not official); 800 sq ft ADU with standard fixture count; FY 2026 fee schedule; Cambrian/Moreland district parcels excluded. Sewer actual depends on fixture count — a full bath + kitchen ADU lands mid-range, not at the cap.
Why Campbell stands out
The $5.40 school fee. Two districts, two fee resolutions, one parcel. Campbell Union School District charges $3.79/sq ft for residential ADUs over 750 sq ft; Campbell Union High School District charges $1.61. Combined: $5.40 — against Pasadena’s $2.24 and the $5.38 tier (Long Beach, Torrance, Anaheim, Fullerton) that used to be the series ceiling. Campbell breaks the ceiling by two cents and a second district. Verify your parcel’s district: parts of Campbell fall under Cambrian or Moreland, with different rates.
Valuation-based permits with a construction tax. Campbell’s FY 2026 schedule (Resolution 13279) prices building permits at 2.00% of the first $500,000 of valuation, plus 33% for plan check, plus a stack of small add-ons (General Plan maintenance 0.16%, technology 0.04%, training 0.02%, Title 24, state seismic and SB 1473 fees). On top: a construction license tax of $0.50 per square foot — $400 on our ADU, a line item most cities bury or skip. Our $100,000-valuation example totals roughly $3,929 all-in for permit-related lines.
The sewer district problem. Campbell’s sewer isn’t the city’s — it’s West Valley Sanitation District, with its own board, its own rate schedule, and per-fixture-unit math. $567.68 per drainage fixture unit (capped at $6,727) plus $86.42 per unit of treatment capacity (capped at $1,024). A typical 800 sq ft ADU with one full bath and a kitchen won’t hit the caps, but the meter is running per fixture in a way no flat-fee city replicates. WVSD’s permit must be in hand before the city issues the building permit — a sequencing detail that has delayed projects.
The county gallery. Instead of a city-run pre-approved plan program, Campbell points to the Santa Clara County ADU Plans Gallery — a 16-jurisdiction collaborative with free and low-cost designs. It’s a different model from Pasadena’s city-designed free plans: broader catalog, less city-specific pre-review.
The 750 sq ft cliff
Standard §66311.5 application: under 750, all three city impact fees are $0; at 800, they’re proportional to the primary dwelling. The school fee has its own threshold — Campbell Union’s $3.79 rate applies to ADUs “over 750 sq. ft.,” creating a double cliff at the same line.
The bottom line
Campbell is the series’ fee-maximalist: the highest school fee we’ve published, valuation-based permits with a per-square-foot construction tax, and the most granular sewer math in the data. At ~$318,000, it ties Fullerton and Garden Grove to the dollar — but built from entirely different parts. In Silicon Valley, even the school districts charge Silicon Valley prices.