Published: 27 Oct 2026 · Last verified: 27 Oct 2026 · Next review: Jan 2027
Three doors into the same outcome — a second housing unit on your lot. Three completely different cost structures.
This page synthesizes our three existing deep-dives — the 800 sq ft detached ADU ($320,000), the garage conversion ($190,000), and the JADU (no published total, by honest design) — into one decision table.
The comparison
| Detached ADU | Garage conversion | JADU | |
|---|---|---|---|
| Size | 800 sq ft (new) | ~450 sq ft (existing shell) | ≤500 sq ft (inside house) |
| Build cost | $320,000 ($400/sq ft) | $190,000 ($422/sq ft) | Not published¹ |
| Impact fees | $0–$10,411 (city-dependent; $0 under 750 sq ft) | $0 (under 750 sq ft) | $0 (by law) |
| School fees | $1,792–$4,320 | ~$2,155 (450 sq ft × rate) | $0 (by law) |
| Utility connections | $0–$10,000+ (city-dependent) | Usually $0 (existing service) | $0 (by law) |
| Parking | None required (state law) | None required | None required |
| Timeline | 9–14 months (permit + build) | 6–10 months | 3–6 months |
| Rental income (LA) | ~$2,400/mo (2BR) | ~$1,600/mo (1BR) | ~$1,200/mo (studio) |
| Can sell separately | Only with AB 1033 ordinance | Only with AB 1033 ordinance | No |
¹No public agency publishes JADU construction costs. We do not invent one — see our JADU post for the honest structure.
Why the per-square-foot lies
The garage conversion costs $422/sq ft — more per foot than the detached ADU’s $400. That number misleads. Conversions concentrate money in the expensive phases (systems, interior) while skipping the cheap ones (foundation, envelope). You pay more per foot for fewer feet. The total — $190,000 vs $320,000 — is what your bank account feels.
The JADU inverts this further: nearly every fee line is $0, three of six construction phases nearly vanish, and the remaining cost concentrates in kitchen, bath, and electrical inside walls that already exist.
The real tradeoffs
Choose detached ADU when: you want maximum rental income, a separate sellable asset (where AB 1033 applies), and full design freedom. It costs the most and returns the most.
Choose garage conversion when: you have an underused garage, want the lowest total outlay for a real one-bedroom unit, and can live without covered parking. Watch for: slab condition, ceiling height (7’6” minimum), and whether the garage shares a wall that complicates fire separation.
Choose JADU when: speed and minimal cost matter most, you can sacrifice a bedroom inside the house, and you accept the 500 sq ft cap and no-short-term-rental rule. It is the only option where the fee schedule reads $0 down the entire column.
The bottom line
$320,000, $190,000, or “no published total but nearly everything is $0” — the cheapest way to add a unit depends on what you are optimizing for. Total outlay: JADU. Rental income per dollar: detached ADU. Speed: JADU. Flexibility: detached. There is no universal winner, which is why the table exists.