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.
Garden Grove is the anti–Santa Maria of this series.
Santa Maria (last week’s post) issues 1,318 ADU permits and publishes almost nothing about what they cost to permit. Garden Grove issued 1,205 ADU permits from 2022 through 2024 — ninth statewide — and publishes everything: a 2026 fee schedule with readable building-permit tiers, a 65% plan-check rate, dollar impact-fee rates, and Ordinance No. 2966, a 2025 ADU ordinance that reads like it was written for people who actually build ADUs. On top of that, the city hands out four free pre-approved ADU plans through its ADU Go program.
The six-phase total below — $318,000, or $398 per square foot — carries three assumptions the city has not confirmed, each marked where it appears: the valuation behind the building permit, the ADU’s share of impact fees, and whether the regional sewer charge applies when the ADU shares the primary home’s connection. We emailed the city’s Building & Safety Division on Oct 6, 2026 with these questions and received no reply by publication. We will update this post when the city responds. Construction phases 2–6 are carried from the Los Angeles County baseline; Garden Grove does not publish phase-level construction costs.
The short answer
| 800 sq ft detached ADU · Garden Grove · 2026 | Amount |
|---|---|
| Total build cost (see assumptions) | $318,000 |
| Cost per square foot | $398 |
| Largest single line | Systems + interior, $147,000 |
| School district fees (GGUSD, verified) | $4,136 |
| OC San sewer capacity charge | $1,710 (rate verified; applicability asked) |
| Building permit + plan check (assumed valuation) | ~$5,176 (assumed) |
| DIF (800 sq ft, assumed interpretation) | ~$4,301 (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 (ADU Go free plans can cut this) |
| Building permit | ~$3,137 | 2026 fee schedule tiers — assumes $250,000 valuation; city method unconfirmed |
| Plan check (65% of permit) | ~$2,039 | 2026 fee schedule — tied to the same assumed valuation |
| Green building +10% / energy +10% (cumulative) | ~$1,087 | Fee schedule surcharge notes |
| School fees (GGUSD) | $4,136 | $5.17/sq ft × 800 — board resolution June 2024, verified |
| DIF — park mitigation (pro-rata example) | ~$3,232 | $6,061 × 800/1,500 — city’s ADU calculation unconfirmed |
| DIF — transportation (pro-rata example) | ~$853 | $1,600 × 800/1,500 — city’s ADU calculation unconfirmed |
| Drainage (pro-rata example) | ~$216 | $0.27 × 800 — city’s ADU calculation unconfirmed |
| OC San capacity charge (CFCC) | $1,710 | OC San Table A average demand rate, verified — whether it applies to a connection-sharing ADU is unconfirmed |
| Water / sewer new connection | $0 | ADU may share primary dwelling’s connections (§9.54.080) |
The two cliffs
Garden Grove has two different exemption cliffs, and they sit at two different sizes.
Cliff one — impact fees at 750. Under 750 sq ft: zero impact fees. At 750 or more: fees proportional to the primary dwelling. For our 800 sq ft build on a 1,500 sq ft house, the example math is ~$4,301 in impact fees — a 749 sq ft design would pay $0. The city’s own ADU Go plan #3 is drawn at exactly 750 sq ft, straddling the line.
Cliff two — school fees at 500. State law (SB 543, effective January 2026) exempts ADUs from school developer fees only at 500 sq ft of interior livable space or less — and the whole unit’s area counts, not just the excess. A 500 sq ft ADU pays $0; a 501 sq ft ADU pays the full $5.17 × 501 ≈ $2,590. Our 800 sq ft build pays the full $4,136.
ADU Go: the free plans
ADU Go (ggcity.org/adu-go) is the city’s pre-approved plan program: four designs from 447 to 1,000 sq ft, free to use, with online submittal. The 750 sq ft two-bedroom is the obvious star — full impact-fee exemption plus no design fees. Using a pre-approved plan also exempts the project from the architectural compatibility requirement. Flood Zone “A” parcels can’t use them.
Garden Grove vs. Los Angeles County
| Garden Grove | LA County baseline | |
|---|---|---|
| Total | $318,000 | $320,000 |
| Per sq ft | $398 | $400 |
| School fees | $4,136 | $4,304 |
| Pre-approved plans | 4, free | none |
The −$2,000 gap is well inside the noise of the three unconfirmed assumptions — treat it as parity, not a discount.
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. Garden Grove’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 three assumptions above are the city’s to confirm. Always verify current fees with the City of Garden Grove Building & Safety Division before budgeting.