Published: 5 Oct 2026 · Last verified: 5 Oct 2026 · Next review: Jan 2027 Cost figures are re-checked against permit records quarterly. Changes are logged in Corrections.
There is exactly one housing type in California with no development impact fees, no school district fees, no water or sewer connection charges, and no parking requirement. It is capped at 500 square feet of interior living space, it must live inside a house that already exists, and most cost guides skip it entirely because there is no official construction-cost data to quote.
This post is about the Junior Accessory Dwelling Unit — and about what happens to the six-phase ledger when three of the six phases structurally collapse to near zero.
One disclosure up front, because it shapes everything below: no public agency publishes JADU-specific construction costs. HCD describes JADUs qualitatively (“reduce development costs”); no city or county fee schedule we found prices a JADU build. So unlike the city posts in this series, this page carries no headline total. What it does carry is fully sourced: every fee line, every legal requirement, and the exact shape of where the money goes. We would rather show you the structure honestly than invent a number.
The short answer
| JADU · California · 2026 | |
|---|---|
| Max size | 500 sq ft interior livable space |
| Location | Inside an existing or proposed single-family home |
| Development impact fees | $0 (barred by statute) |
| School district fees | $0 (for JADUs under 500 sq ft, since 2026) |
| Water/sewer connection + capacity charges | $0 |
| New parking required | None |
| Building permit + plan check | Applies (standard alteration rates) |
| Where the money goes | Systems + interior, plus compressed soft costs |
What the six phases look like for a JADU
The same six phases — but a JADU is a conversion inside an existing house, so the ledger collapses:
| Phase | New detached ADU (800 sq ft) | JADU (≤500 sq ft) |
|---|---|---|
| Soft costs | $28,000–$40,000 | Compressed — permit + plan check + deed-restriction recording; every fee below is $0 |
| Site work + foundation | $38,000 | ≈ $0 — existing foundation and slab |
| Framing + structure | $48,000 | Minimal — partition walls, doorway openings |
| Building envelope | $42,000 | Minimal — new exterior entry door |
| Systems + interior | $147,000 | The cost center — efficiency kitchen, bathroom, electrical, HVAC tie-in, finishes |
| Landscaping & hardscape | $13,000 | ≈ $0 — no site work |
| Structural total | $320,000 | No official total exists |
Three phases vanish by definition. The entire economic question of a JADU reduces to two lines: how much are your systems and interior, and how small are your soft costs. Everything else in this post is about keeping both honest.
The fee autopsy: a column of zeros
Every fee a city normally attaches to an ADU, checked against statute for a qualifying JADU:
| Fee | JADU (≤500 sq ft) | Authority |
|---|---|---|
| Development impact fees | $0 — barred | Gov. Code §66311.5(c)(1) |
| School district developer fees | $0 (under 500 sq ft) | §66311.5(c)(3) via Ed. Code §17620 — new in 2026 (SB 543) |
| Water/sewer connection + capacity charges | $0 — may not be treated as a new dwelling unit | §66311.5(b) |
| New or separate utility connections | Cannot be required | §66311.5(d) |
| New parking | Cannot be required | ABAG state-law summary |
| Building permit + plan check | Applies — standard rates, no ADU surcharge | Local fee schedule (alteration/remodel rates) |
Two precision notes, because the boundaries matter:
- The impact-fee bar is “500 square feet or less” (≤500). The school-fee bar is “less than 500” (<500). A JADU drawn at exactly 500 sq ft sits on the school-fee boundary — draw at 499 or below to stay clearly exempt.
- If the JADU converts space in an attached garage, replacement parking for the garage may be required even though no new parking is required for the JADU itself.
What 2026 changed
Two bills rewrote the JADU economics this year:
SB 543 — school fees gone. Before 2026, school district developer fees were the one fee that ignored every ADU size exemption. Now, JADUs under 500 sq ft of interior living space are not treated as adding assessable space at all — the fee is zero by statute, not by district goodwill.
AB 1154 — owner-occupancy narrowed. The old rule required the owner to live on the property, period. Now owner-occupancy is required only when the JADU shares its bathroom with the main house — and even then, the owner may live in either unit. A JADU with its own bathroom has no owner-occupancy requirement. What did not change: a deed restriction must be recorded in every case, running with the land, prohibiting separate sale of the JADU.
The bathroom decision
This is the single highest-leverage choice in a JADU project, and it is a trade-off, not a free lunch:
| Share the bathroom | Separate bathroom | |
|---|---|---|
| Plumbing cost | Lower — tie into existing | Higher — new rough-in, fixtures, venting |
| Owner-occupancy | Required (either unit) | Not required |
| Privacy / rentability | Lower | Higher |
| HCD’s own framing | “may share a bathroom with the primary dwelling, all to reduce development costs” | — |
Sharing the bathroom is the cheapest path HCD itself describes. Separating it costs more in plumbing but removes the owner-occupancy condition entirely — which matters if the goal is a fully independent rental or a future sale of the whole property unencumbered by residency strings.
JADU vs. ADU vs. garage conversion
| JADU | Standard ADU | Garage conversion | |
|---|---|---|---|
| Max size | 500 sq ft interior | 800–1,200 sq ft (by type) | Per ADU rules |
| Location | Inside the house | Anywhere on lot (setbacks apply) | Existing garage |
| Per lot | 1 | Detached 1 + conversion 1 + JADU 1 possible | Counts as conversion ADU |
| Owner-occupancy | Shared bath only | Not required | Not required |
| Separate sale | Never (deed restriction) | Possible (AB 1033 condo, conditional) | Per ADU rules |
| Impact fees | $0 (≤500) | $0 (≤750), proportional above | $0 (≤750), proportional above |
| School fees | $0 (<500, since 2026) | Possible at 500+ | Possible at 500+ |
| Utility connections | Cannot be required | Conversions: cannot be required; new builds: proportional possible | Cannot be required |
| Parking | None required | Varies (garage demolition: no replacement needed) | None required |
| Sprinklers | Only if main house has them | Only if main house has them | Only if main house has them |
| Rental term | 30+ days only | 30+ days only | 30+ days only |
Note the stacking row: on a single-family lot, state law as interpreted by HCD allows one detached ADU + one conversion ADU + one JADU — three units where one house stood. The JADU is the cheapest of the three to add because two of its cost phases do not exist.
What moves the number most in a JADU
1. Bathroom: shared vs. separate. Covered above — the largest single cost decision and the largest legal decision, in one.
2. The efficiency kitchen. Required by statute: cooking appliances, food-preparation counter, and storage proportional to the unit. A kitchenette with plug-in appliances (which HCD explicitly contemplates) costs a fraction of a full rough-in — but check what your building department accepts before budgeting around it.
3. Electrical service and HVAC tie-in. HCD notes JADUs “may share central systems.” If the existing panel and furnace have capacity, the tie-in is modest. If the panel needs an upgrade or the HVAC needs a new zone or mini-split, this becomes the second-biggest line after the bathroom.
4. The entry door. A JADU needs its own exterior entrance, separate from the main house’s front door. Cutting a new opening in an existing wall — with header, flashing, and landing — is the only “envelope” cost, and on some floor plans it is the only structural work at all. (Up to 150 sq ft of expansion is allowed solely to accommodate ingress/egress.)
5. Deed restriction recording. Required in every case. The county recorder’s standard recording fees apply; no JADU-specific amount is published.
What we do not know (stated plainly)
- No official JADU construction total exists. HCD, DBI, and every city and county fee schedule we checked publish no JADU-specific construction costs. Contractor-published ranges exist but are not public records, so we do not use them. If your jurisdiction publishes one, we want it — see Corrections.
- Permit and plan-check fees follow standard alteration/remodel rates, which vary by jurisdiction. No JADU-specific rate table was found.
- Deed-restriction recording costs are standard county recorder fees; no JADU-specific figure is published.
→ The 800 sq ft detached baseline this converts from: 800 sq ft ADU cost
→ Where the 750 sq ft cliff still bites: San Diego ADU cost · Sacramento ADU cost
Put your own quote in these six rows
We made a blank version of the six-phase ledger. Drop your contractor’s numbers into it and see which line doesn’t match ours.
Download the worksheet — CSV (import to Google Sheets), no email required
Compare any two builds side by side →
Want the regional benchmark ranges for each phase, updated quarterly?
Methodology and sources
Every figure on this page is traced to a named, checkable source. Where no official figure exists, we say so instead of modeling one.
| Input | Source |
|---|---|
| JADU definition (≤500 sq ft interior, inside single-family home) | Gov. Code §66313(d) |
| JADU approval requirements (one per lot, deed restriction, efficiency kitchen, 30-day rental minimum) | Gov. Code §66333 (as amended by AB 1154) |
| Impact-fee bar (≤500 sq ft) and school-fee bar (<500 sq ft) | Gov. Code §66311.5(c) (SB 543, eff. 1 Jan 2026) |
| Utility connection protections | Gov. Code §66311.5(b), (d) |
| Owner-occupancy narrowing (shared bathroom only) | AB 1154 analysis · Gov. Code §66333(b) |
| HCD’s qualitative cost framing | HCD ADU program page |
| State-law summary (parking, conversions, three-unit stacking) | ABAG State Laws Summary and Checklist (Jul 2025) |
| Sprinkler rules | Burbank water permit requirements · CAL FIRE IB 25-004 |
| SB 543 bill analysis | Assembly committee analysis |
Check this against your own jurisdiction
- Open your city’s ADU page and confirm it follows the state JADU articles (some cities add local objective standards).
- Ask the building counter which alteration/remodel rate table applies to interior JADU conversions — there is no JADU-specific schedule.
- Confirm the school district boundary for your address: the <500 sq ft exemption is statutory, but districts administer it.
If your city’s numbers diverge from the statute as described here, we want to know. See Corrections.
Our position
We don’t build ADUs. We don’t sell plans. We don’t sell your information to contractors. No figure on this site has been paid for or reviewed by anyone whose costs we publish. More on About.
This page describes California JADU law and fee structure as of 2026. It is construction cost information — not a quote, and not legal, engineering, or financial advice. Confirm requirements with your local building department and a licensed California contractor.
Frequently asked questions
What is a JADU in California?
A Junior Accessory Dwelling Unit: a unit of no more than 500 square feet of interior livable space, contained entirely within an existing or proposed single-family home, with its own exterior entrance and an efficiency kitchen. The bathroom may be shared with the main house or separate. One JADU per single-family lot (Gov. Code §66313, §66333).
How much does a JADU cost in California in 2026?
No public agency publishes JADU-specific construction costs, so we do not print a headline total. Structurally, a JADU eliminates three of the six cost phases almost entirely — no site work or foundation, no building envelope, no landscaping — because the unit lives inside an existing house. The real costs concentrate in systems and interior (efficiency kitchen, bathroom, electrical, HVAC) plus compressed soft costs. Every fee line that normally applies to ADUs is $0 for a qualifying JADU.
Are there really no fees on a JADU?
On impact fees, school district fees, water and sewer connection and capacity charges, and new parking: effectively yes, for a JADU of 500 square feet or less. Development impact fees are barred by Gov. Code §66311.5(c)(1); school fees are barred for JADUs under 500 sq ft since 2026 (SB 543); utilities may not treat a JADU as a new dwelling unit for connection-fee purposes; and no new parking may be required. Standard building permit and plan-check fees still apply.
Do I have to live on the property with a JADU?
Only if the JADU shares its bathroom with the main house. Since AB 1154 (effective January 2026), the owner-occupancy requirement applies solely to shared-bathroom JADUs — and even then, the owner may live in either the main house or the JADU. A JADU with its own bathroom has no owner-occupancy requirement. A deed restriction is recorded in all cases, prohibiting separate sale of the JADU.
Can I rent out a JADU?
Yes, for tenancies longer than 30 days. Short-term rental of a JADU is prohibited by statute.