What Is a JADU? A Homeowner's Guide to Finding a Junior ADU Builder

What Is a JADU? A Homeowner's Guide to Finding a Junior ADU Builder

A JADU is the cheapest legal way to add a second living space to a California single-family home — and the least understood of the four ADU types. Before you start calling contractors, it pays to know exactly what a junior ADU is, which rules come with it, and why the right JADU builder looks more like a sharp remodeling contractor than a backyard-cottage company.

The 30-second answer

A JADU (junior accessory dwelling unit) is a unit of up to 500 square feet created within the existing walls of your single-family home — typically a converted bedroom, den, or attached garage. It needs an efficiency kitchen and its own exterior entrance, it can share a bathroom with the main house, and the owner must live on the property. Expect roughly $60,000–$140,000 and 3–6 months of construction. The right JADU builder is a CSLB-licensed contractor (usually Class B) with real conversion and permitting experience — a directory profile like Quality First Builders is a good example of what to look for: license status, services, and reviews in one place, already pre-screened.

What legally counts as a JADU in California

The "junior" in junior ADU is doing real work. Four requirements separate a JADU from every other ADU type:

• 500 square feet, maximum. A JADU is capped at 500 sq ft and must be carved out of the existing walls of your single-family home. You're not adding a structure — you're converting space you already own: a spare bedroom, a den, or an attached garage that's part of the house footprint.
• An efficiency kitchen, not a full one. The law requires a cooking appliance (often a plug-in cooktop), a sink, and a small counter and storage area. No range hood battles, no full appliance package.
• Its own exterior entrance. The unit needs a door to the outside, separate from your front door. This is usually the biggest piece of "new construction" in the whole project. An interior connecting door to the main house is allowed too.
• A bathroom it can borrow. A JADU may share a bathroom with the main house. That single provision is why junior units are so much cheaper — you may not be adding a bathroom or touching the sewer line at all.

A standard ADU plays by different rules: the state guarantees at least 800 sq ft, the City of Los Angeles allows detached units up to 1,200 sq ft, and a full kitchen and bathroom are required. For the complete side-by-side, see our ADU vs JADU comparison and the broader guide to the types of ADUs in California.

The rules that surprise homeowners

Two strings are attached to a JADU, and one big break comes with it.

Owner-occupancy is mandatory — and permanent

With a JADU, the property owner must live on-site, either in the main house or in the junior unit itself. You can rent out the other space, but you can't move away and rent both. Unlike some standard-ADU rules that sunset, this one is permanent state law. If your endgame is turning the whole property into a rental, that requirement usually pushes people toward a standard ADU instead — a good builder will raise this on the first call, and it's a useful honesty test if they don't.

No short-term rentals in LA

If you're in Los Angeles, plan on long-term tenants: the city prohibits using an ADU as a short-term rental, meaning any stay under 30 days is not allowed. JADUs are intended as housing, not Airbnb inventory.

The break: no parking, no impact fees

A JADU requires no additional parking, period. And because any ADU under 750 sq ft is exempt from local impact fees under SB 13, every JADU qualifies — a fee category that can run thousands of dollars on larger projects simply doesn't apply to yours.

What a JADU costs, and how long it takes

Here's how the junior unit stacks up against the other ADU types on all-in cost and construction time:

For context, the statewide median ADU in California runs about $150,000, and roughly 71% cost under $200,000 — a JADU sits comfortably below both marks. On the permitting side, California caps plan check at 60 days for a complete, compliant application, and approval is ministerial — no public hearing, no design review. Where a full custom ADU journey runs about 8–14 months from design to move-in, a JADU conversion sits at the short end of everything: less design, less plan check back-and-forth, less construction.

One financing note: the CalHFA $40,000 ADU grant you may have read about is currently paused and out of funds, with no confirmed relaunch. Most homeowners fund a JADU with savings, home equity, or a renovation loan — at this budget level, that's far more attainable than for a detached build.

Is "JADU builder" actually a specialty?

Sort of — but not the way you'd think. There's no special JADU license, and you shouldn't expect to find contractors who build junior units exclusively. The work itself is remodeling-grade: an interior conversion, a new exterior door, an efficiency kitchen, maybe a bathroom, plus the permit path. What you're really shopping for is a general building (Class B) contractor who has run ADU and JADU permits before — because the trap in a JADU project isn't the construction, it's the compliance details.

A builder who knows JADUs will do three things a generic remodeler won't:

1. Audit the space first. Not every room converts cleanly. Ceiling heights, egress, the location of the future exterior door, and how the efficiency kitchen and shared-bathroom access lay out all determine whether your 500 square feet actually works as a dwelling.
2. Own the permit path. Your builder should pull the permit and manage plan check — that's their job, not yours. Every legal ADU needs approved plans, permits, and inspections, even a small one carved from a bedroom.
3. Tell you when a JADU is the wrong call. If your goal is maximum rent with no owner-occupancy strings, an honest contractor says so before taking your deposit.

Design-build firms are a natural fit here because plans, permits, and construction stay under one roof. On our directory, Quality First Builders is the kind of profile to start with — like every builder we list, they've been pre-screened for an active CSLB license before we'll introduce them.

How to vet a JADU builder before you sign

Whether you find a contractor through us or anywhere else, run this checklist:

• Active CSLB license, right classification. Usually Class B General Building. Verify free at cslb.ca.gov: status ACTIVE, bond on file, workers' comp current. California requires the license number on all ads and contracts — if it's missing from a proposal, walk.
• Verifiable recent conversion work. Ask for addresses or photos of completed ADU or JADU projects nearby, not just kitchen remodels.
• A fully itemized, fixed-price quote. Every line named — including any electrical or plumbing work the conversion triggers. Vague allowances are where budgets die.
• A legal deposit. California caps a contractor's down payment at $1,000 or 10% of the contract, whichever is less. On any JADU, that means $1,000 max up front. A 30–50% deposit ask is a red flag, full stop.
• Honest scheduling. Be skeptical of anyone guaranteeing a fixed "60-day approval" — that statutory cap applies only to a complete application, and it isn't a build timeline. A good builder gives you a project-specific schedule instead of a slogan.

Smart questions for the first call

• Have you built a JADU specifically — not just standard ADUs? What did the efficiency kitchen look like?
• Who produces the plans, and do you handle plan check and inspections end to end?
• Does my room actually convert — ceiling height, egress, entrance location — or should we look at a different space?
• What happens to the price if the city requires upgrades we didn't anticipate?
• What's the payment schedule after the initial deposit, and is it tied to milestones?

The answers matter less than the texture of them. A contractor who has done this work answers in specifics — door placement, plan-check comments they've dealt with, what the inspector looks for. One who hasn't will keep steering the conversation back to price.

The combo play: JADU plus ADU

One more thing worth knowing before you brief a builder: on a single-family lot, California allows one standard ADU plus one JADU. Homeowners increasingly phase it — the low-cost junior unit first (aging parent, boomerang kid, modest rental income), then a detached backyard unit later once the first project proves out. If that's your trajectory, say so up front: it changes where the JADU's entrance goes, how utilities are planned, and which builder makes sense for the long run.

The next step

If your spare bedroom or attached garage is sitting idle, a JADU is the lowest-risk way to turn it into legal living space — roughly $60,000–$140,000, 3–6 months of construction, and no parking or impact-fee headaches. The whole project rises or falls on the contractor, so start where the vetting is already done: review the Quality First Builders profile on our directory, or compare vetted ADU builders in Los Angeles side by side. Every builder we list holds an active, verified CSLB license and has cleared red-flag screening — tell us about your space and we'll request an intro to a pro who fits.

One honest note: 1-800-ADU-Pros is a referral and pre-qualification service, not a contractor — we don't build anything ourselves. All work is performed by independent, California-licensed builders, and each builder's CSLB license number is shown on their profile so you can verify it yourself at cslb.ca.gov.