ADU by size

500 Sq Ft ADU: The JADU Boundary and the One-Bedroom Sweet Spot

Five hundred square feet is the most interesting number in ADU planning — it’s the legal ceiling for a JADU and the floor of the comfortable one-bedroom.

The short version

A 500 sq ft ADU is a true one-bedroom — and 500 sq ft is also the legal maximum for a Junior ADU (JADU), which must sit within the walls of your existing house. That gives you two very different paths at the same size: a JADU carved out of existing space for a flat $60K–$130K, or a custom detached backyard unit for $200K–$230K at our published 2026 rates.

The numbers at a glance

Typical layout	True one-bedroom
The legal line	500 sq ft is the JADU maximum (inside the existing home)
JADU path (2026)	$60K–$130K
Custom detached (2026)	$200K–$230K at published rates
Approval	Ministerial — 60-day clock, no hearing

Browse by size: 400 sq ft · 500 sq ft · 800 sq ft · 1,200 sq ft — or see our floor plans.

What this size costs, by build type (2026)

Build type	Typical 2026 range
Garage conversion (2-car garage footprint)	$90K–$150K
Junior ADU (500 sq ft is the JADU legal max)	$60K–$130K
Custom detached ADU (new backyard build)	$200K–$230K

Ranges at our published 2026 rates; final pricing depends on site conditions — panel, utilities, slope, access. Run your exact size in the cost calculator.

Two legal paths at the same size

At 500 square feet you are standing on a legal boundary. Inside the house, state law defines the JADU: no more than 500 sq ft of interior livable space, within the existing or proposed single-family home (an attached garage qualifies), with a separate entrance and an efficiency kitchen. Outside, the same square footage becomes a standard detached ADU with no such constraints. Same number, different law, very different budgets — our JADU guide covers the inside path in detail.

What 500 square feet lives like

This is where a one-bedroom stops feeling like a compromise: a bedroom that takes a queen bed and a dresser, a living area that holds a sofa and a small dining table at once, a kitchen with real counter run, and a full bathroom. Our Laguna (450 sq ft) and Balboa (550 sq ft) plans bracket this size — the Balboa is the one we build most, because it matches the deepest slice of the tenant market.

Choosing between JADU and detached

The JADU wins on budget ($60K–$130K, because the shell already exists) and on speed; it costs you interior space in the main house and shares its walls. The detached unit wins on privacy, rentability and long-term value; it costs more ($200K–$230K) and needs yard room. One consideration that surprises owners: under 2026 law a JADU that shares sanitation facilities with the main house carries an owner-occupancy requirement — one with its own bathroom does not. We walk both paths on the free site visit, with the calculator math for each.

Living area of a completed L Square ADU — real project photography.

Frequently asked questions

What is the difference between a 500 sq ft ADU and a JADU?

Location and law. A JADU is capped at 500 sq ft of interior livable space and must sit within the walls of the existing or proposed single-family home; a detached 500 sq ft ADU is a standalone backyard home under the standard ADU rules. The JADU path typically runs $60K–$130K; the detached path $200K–$230K.

Does a 500 sq ft ADU need its own bathroom?

A standard ADU always has its own full bathroom. A JADU may share sanitation facilities with the main house — but under the 2026 rules, sharing triggers an owner-occupancy requirement, while a JADU with its own bathroom carries none.

What does a 500 sq ft ADU rent for?

Within the published Orange County band of $1,800–$4,000 a month, a well-finished one-bedroom of this size typically lands low-to-middle of its city's range — see the city-by-city rent table on our ADU ROI page.

How much does a 500 sq ft ADU cost?

As a custom detached build, typically $200K–$230K at our published 2026 rates. As a JADU inside your existing home, a flat $60K–$130K. As part of a 2-car garage conversion, $90K–$150K. Site conditions decide where you land — run your lot in the cost calculator.

Can I have both a JADU and a detached ADU on one lot?

Yes — state law lets a single-family property add one ADU and one JADU. Owners often carve the 500 sq ft JADU from existing space first, then add the detached unit later as budget allows.

What setbacks apply to a 500 sq ft detached ADU?

4-ft side and rear setbacks, with at least 16 feet of height protected on the by-right path — generous margins for a footprint this size, which is why 500 sq ft fits lots that look too tight at first glance.

Check what your property allows

Tell us your city and address — we’ll come back with what your lot allows and a free estimate.

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