Published: 10 Oct 2026 · Last verified: 9 Oct 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
Riverside’s building permit for an 800 sq ft ADU costs $1,006. Burbank charges $3,692 for the same piece of paper. That $2,686 gap is not a rounding error — it is the difference between a city that prices permits by the square foot and cities that price them by construction valuation, and it is the single biggest reason Riverside lands at $309,000, the lowest total this series has published.
The math is refreshingly legible. Riverside’s Building & Safety Fee Schedule (June 2025) lists new single-family R-3 construction at $0.53 per square foot for plan check plus $0.53 per square foot for the permit — $424 + $424 on 800 sq ft — then adds a $39 issuance fee, a 10% General Plan maintenance fee ($84.80), and a 4% technology fee ($33.92). Total: $1,005.72, which we round to $1,006. There is no ADU-specific line in the schedule, so we applied the new single-family rate to a detached ADU; the city has not confirmed that classification, and it is the first of seven open questions at the bottom of this post.
The second reason Riverside is cheap is paper you do not have to pay an architect to draw. Dwell Riverside, the city’s pre-approved ADU program, publishes four free permit-ready detached plan sets — 746, 800, 1,020, and 1,200 square feet — and the 800 sq ft 2-bedroom/2-bath design matches this post’s benchmark size exactly. No other city in the series has a free plan at the exact size we price. The plans are free; the site-specific work (foundation, placement, soils) is not, so we do not zero out design costs — but the savings are real.
Seven assumptions sit underneath the $309,000 total, each marked where it appears: the permit-fee classification, the planning review fee ($378 vs $93), current park and transportation DIF rates (our sources are 2022–2023), whether the $4,284 sewer fee applies to ADUs in full, the school district’s fee resolution, and the design-cost savings from Dwell Riverside. Construction phases 2–6 are carried from the Los Angeles County baseline; Riverside does not publish phase-level construction costs.
The short answer
| 800 sq ft detached ADU · Riverside · 2026 | Amount |
|---|---|
| Total build cost (see assumptions) | ~$309,000 |
| Cost per square foot | ~$386 |
| Largest single line | Systems + interior, $147,000 |
| Building permit + plan check | $1,006 (series low) |
| DIF — park, pro-rata example | ~$1,484 (2022 rate, unconfirmed) |
| School district fee (RUSD) | $4,136 |
| Sewer capacity charge | $4,284 (ADU applicability unconfirmed) |
| Free pre-approved plans | 4 designs, incl. 800 sq ft |
| 750 sq ft cliff | Yes — Title 19 |
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) | ~$21,000 | 7% |
| Site work + foundation | $38,000 | 12% |
| Framing + structure | $48,000 | 15% |
| Building envelope | $42,000 | 14% |
| Systems + interior | $147,000 | 48% |
| Landscaping & hardscape | $13,000 | 4% |
| Total | ~$309,000 | ~$386 / 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 — Dwell Riverside plans are free but site-specific work costs money (savings unquantified) |
| Building permit | $424 | 800 × $0.53/sq ft — Building & Safety Fee Schedule (Jun 2025) |
| Plan check | $424 | 800 × $0.53/sq ft — same schedule |
| Permit issuance | $39 | Same schedule |
| General Plan maintenance | $84.80 | 10% of (permit + plan check) — same schedule |
| Technology fee | $33.92 | 4% of (permit + plan check) — same schedule |
| Planning review | $378* | Zoning Plan Check, new SFR — Planning Fee Schedule Res 24253 (ADU applicability unconfirmed) |
| Park DIF | ~$1,484* | $3,340/unit × (800/1,800) — 2022 handout rate, current rate unconfirmed; our arithmetic, not a city figure |
| School fee (RUSD) | $4,136 | $5.17/sq ft × 800 — RUSD developer fee page (resolution number unconfirmed) |
| Sewer capacity | $4,284* | Per-unit rate, Public Works Development Fees (Jul 2023) — ADU applicability unconfirmed |
Against the series baseline
| Riverside | LA County baseline | |
|---|---|---|
| Total | ~$309,000 | $320,000 |
| Per sq ft | ~$386 | $400 |
| Building permit + plan check | $1,006 (series low) | carried |
| DIF | ~$1,484 pro-rata (2022 rate) | carried |
| School fee | $4,136 ($5.17) | $4,304 |
| Sewer capacity charge | $4,284* (unconfirmed) | carried |
| Free pre-approved plans | 4 designs, 800 sq ft match | none |
| ADU permits 2022–2024 (HCD) | 762, 16th statewide | — |
The $11,000 gap to the baseline is mostly the permit bill: $1,006 here against a carried baseline, plus a school fee one tier below the $5.38 maximum. If the $4,284 sewer charge does not apply to ADUs in full — plausible, since state law bars treating ADUs as new dwelling units for capacity charges — the honest floor drops toward $305,000. If the planning review lands at $93 instead of $378, shave another $285. The composition is the story: the cheapest permit in the series, a free 800 sq ft plan set, and mid-tier everything else.
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. Riverside’s pro-rata structure will need marginal math — an 800 sq ft ADU would owe park DIF on 50 sq ft, not 800, which requires a per-square-foot park rate the current handout does not publish in ADU terms. We found no mention of SB 1117 in city materials; the January 2027 quarterly review will check for a revised fee schedule. School fees are outside SB 1117’s impact-fee definition and stay at $4,136.
Disclaimer
Model estimate, not a quote. Fees change; the assumptions above are the city’s to confirm — the permit-fee classification, the planning review fee, current DIF rates, sewer applicability, the school district resolution, and Dwell Riverside savings are all marked where they appear. Always verify current fees with the City of Riverside Community Development Department before budgeting.