Published: 7 Oct 2026 · Last verified: 7 Oct 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
Fullerton has the cheapest building permit in this series — and one of the most expensive park fees. That tension is the whole story.
The FY 2025–2026 fee schedule prices a $250,000-valuation building permit at $1,223, about 39% of Garden Grove’s $3,137 for the same valuation. But the permit is only the cover charge: plan review runs 87% of the permit fee, energy plan check another 20%, and the Park Dwelling Fee — $12,020 per unit — is the single largest impact-fee line we have seen in any city so far. Our six-phase total lands at $318,000, or $398 per square foot — the same headline number as Garden Grove, built from completely different parts.
Three assumptions sit underneath that total, each marked where it appears: the valuation behind the building permit, the ADU’s share of park impact fees, and whether the regional sewer charge applies to an ADU the ordinance says is “not a new residential use.” We have not yet contacted the city about these items; this post will be updated when we do. Construction phases 2–6 are carried from the Los Angeles County baseline; Fullerton does not publish phase-level construction costs.
The short answer
| 800 sq ft detached ADU · Fullerton · 2026 | Amount |
|---|---|
| Total build cost (see assumptions) | $318,000 |
| Cost per square foot | $398 |
| Largest single line | Systems + interior, $147,000 |
| School district fees (two districts) | $4,304 |
| OC San sewer capacity charge | $1,710 (rate verified; applicability unconfirmed) |
| Building permit + plan review + energy (assumed valuation) | ~$2,532 (assumed) |
| DIF — park dwelling, pro-rata (assumed interpretation) | ~$6,411 (assumed) |
The full line-item breakdown
Six phases. The same six used on every build in this series.
| Phase | Cost | Share |
|---|---|---|
| Soft costs (design, permits, fees) | $30,000 | 10% |
| Site work + foundation | $38,000 | 12% |
| Framing + structure | $48,000 | 15% |
| Building envelope | $42,000 | 13% |
| Systems + interior | $147,000 | 46% |
| Landscaping & hardscape | $13,000 | 4% |
| Total | $318,000 | $398 / sq ft |
The fee autopsy
Every fee line we found, with exactly what it is and where it came from.
| Fee line | Amount | Source / status |
|---|---|---|
| Design & engineering | $14,000 | Series baseline, carried (pre-approved plans still in development) |
| Building permit | ~$1,223 | FY 2025–2026 fee schedule tiers — assumes $250,000 valuation; city’s ADU valuation method unconfirmed |
| Plan review (87% of permit) | ~$1,064 | Fee schedule — tied to the same assumed valuation |
| Energy plan check (20% of permit) | ~$245 | Fee schedule, per CA Public Resources Code |
| NPDES (5% of permit) | ~$61 | Fee schedule surcharge |
| General Plan Update Fee | ~$500 | $2 per $1,000 of valuation |
| Permit issuance + system surcharge | ~$78 | $63 + $15, fee schedule |
| School fees (FSD + FJUHSD) | $4,304 | $5.38/sq ft × 800 — FJUHSD $1.79 verified in 2026 study; FSD $3.59 is the statutory-max split, individual adoption unconfirmed |
| DIF — park dwelling (pro-rata example) | ~$6,411 | $12,020 × 800/1,500 — city’s ADU calculation unconfirmed |
| OC San capacity charge (CFCC) | $1,710 | OC San Table A average demand rate, verified — whether it applies to an ADU that is “not a new residential use” is unconfirmed |
| City water / sewer connection | $0 | Existing connections used; ADU “shall not be considered a new residential use” (Ord. 3343) |
The cheapest permit in the series
Fullerton’s building-permit tiers are strikingly low. At a $250,000 valuation the permit is $623 for the first $100,000 plus $4.00 per additional $1,000 — $1,223 total. Garden Grove charges $3,137 for the same valuation. But Fullerton stacks percentage-based reviews on top: 87% plan review ($1,064), 20% energy check ($245), 5% NPDES ($61). The permit-plus-reviews bundle is ~$2,593 — still the lowest in the series, just less dramatically so.
One more wrinkle: the fee schedule lists “Residential Addition $88.00/sq ft” as a valuation shortcut, and the ordinance says valuation follows the ICC Building Valuation Data. Which one the city actually applies to a detached ADU is unconfirmed — at $88/sq ft, an 800 sq ft ADU values at just $70,400, which would cut the permit roughly in half.
The 750 cliff
Ordinance No. 3343 (June 2025) draws the familiar line: no impact fees under 750 sq ft, proportional fees at 750 and above. The ordinance cites Government Code §66324 only for the definition of “impact fee” — the ADU rules themselves live in §66311.5, which the ordinance follows.
The cliff matters more here than in most cities because the Park Dwelling Fee is so large: $12,020 per unit. Our pro-rata example (800 sq ft ADU on a 1,500 sq ft house) puts the ADU’s share at ~$6,411 — a 749 sq ft design would pay $0. And the city’s own in-development pre-approved plan at 842 sq ft sails right past the cliff. If the city ever publishes those plans, the 440 sq ft one will be the fee-optimized pick.
Pre-approved plans: coming soon, maybe
Fullerton’s planning department announced three pre-approved ADU designs (440, 842, and 1,000 sq ft) with RRM Design Group, targeting a spring 2026 public release. As of October 2026, the city’s ADU page shows no trace of them. The ordinance sweetens the deal for whenever they arrive: using a pre-approved plan (or a plan already approved in the same code cycle) cuts the city’s review clock from 60 days to 30 days.
Fullerton vs. Los Angeles County
| Fullerton | LA County baseline | |
|---|---|---|
| Total | $318,000 | $320,000 |
| Per sq ft | $398 | $400 |
| Building permit (+ reviews) | ~$2,593 | carried |
| School fees | $4,304 | $4,304 |
| Pre-approved plans | 3, in development | none |
| ADU permits 2021 → 2025 | 60 → 168 | — |
The −$2,000 gap is well inside the noise of the three unconfirmed assumptions — treat it as parity, not a discount. The real story is the composition: the cheapest permit in the series paired with the priciest park fee.
A note on SB 1117
Signed September 2026, effective January 2027: for a homeowner’s first two ADUs, impact fees may apply only to square footage above 750, calculated marginally. Fullerton’s current pro-rata-on-the-primary-dwelling structure will need a rewrite. We found no mention of SB 1117 in city materials; the January 2027 quarterly review will check for an updated ordinance.
Disclaimer
Model estimate, not a quote. Fees change; the assumptions above are the city’s to confirm — we have not yet contacted the City of Fullerton about the five unconfirmed items, and this post will be updated when we do. Always verify current fees with the City of Fullerton Community and Economic Development Department before budgeting.