Junior ADU (JADU) Design — The Most Affordable Way to Add a Unit to Your Home
A Junior Accessory Dwelling Unit (JADU) is a small, self-contained living space of up to 500 square feet of interior livable space, created entirely within your existing single-family home. JADUs include their own entrance and a cooking facility, and may share a bathroom with the main residence or have their own.
Because a JADU is carved from existing space, it requires no new foundation, no new exterior walls, and minimal structural work. This makes it the fastest and most affordable ADU option available to California homeowners.
Why Homeowners Choose JADUs
Lowest cost — no foundation, framing, or roofing. Conversion costs are a fraction of new construction.
Fully exempt from development impact fees and school fees under current California law
No fire sprinkler requirement if the main home does not already have sprinklers
Fastest Permitting timeline — cities must process JADU applications within 60 days
Can be built in addition to a full-size ADU on the same property — giving you two additional units
JADU vs. ADU — Key Differences
Feature | JADU | Standard ADU |
Maximum size | 500 sq ft | 850–1,200 sq ft |
Location | Within existing home | Attached or detached |
New foundation | No | Often yes |
Bathroom | Own or shared | Own (required) |
Impact fees | Fully exempt | Exempt under 750 sq ft |
Owner occupancy | Required* | Not required |
Short-term rental | Not allowed | Check local rules |
*Owner occupancy is required unless the JADU has its own separate bathroom, per AB 1154 (effective January 2026).
What We Design
Even though JADUs are small, they still require a complete plan set for permit approval:
Space planning: We optimize layouts within the 500 sq ft limit to include a sleeping area, living space, kitchenette, and bathroom.
Separate entrance: Required by law. We design an independent entry that maintains privacy for both units.
Cooking facility: At minimum, a kitchenette with a sink, counter, and small cooking appliance hookup. Full kitchens are also an option.
Fire separation: Fire-rated wall or ceiling assemblies between the JADU and the rest of the home.
Title 24 & CALGreen: Energy and green building compliance documents.
Best Candidates for a JADU
JADUs work especially well in homes that have a spare bedroom, large bonus room, or underutilized section of the house near an exterior wall. Common conversions include master suites, in-law quarters, large laundry/utility rooms, or enclosed patios.
You can also build a JADU in combination with a detached or attached ADU on the same lot. This means one single-family property can have up to three units total — the main home, a JADU, and a standard ADU.
Want to explore whether a JADU works in your home? Get a free feasibility report — we’ll assess your space and walk you through the options.
