A junior ADU is the smallest legal home you can add to a single-family property in California, and most Los Angeles owners never price one. They go straight to a backyard unit, see a six-figure number, and stop. A junior ADU (JADU) sits inside the walls you already have, which changes the cost, the schedule and the risk.
A junior ADU is a small, self-contained unit carved out of an existing single-family home. State rules cap it at 500 square feet and keep it within the footprint of the house. It needs its own entrance from the outside and at least an efficiency kitchen. Because it lives inside the existing structure, it does not need a new foundation, new framing for a separate building or a new roofline.
A full ADU is a different project. It is a separate building or an addition with its own foundation, utilities and structure. If you want to compare the types, our ADUs and additions page lists each one.
Most owners who ask about a junior ADU are not ready to commit to a large build. They want to test the idea: does a rental unit make sense on this property, will a parent or adult child use the space, can the numbers work without a big loan?
A junior ADU answers those questions with less exposure. The work happens inside the house, so there is no excavation, no new foundation and far less site disruption. The structure is already there, which means fewer unknowns and a shorter list of things that can go wrong. You can often stay on the property while the work is under way.
The smaller scope also tends to shorten the build. We have seen garage conversions of this size finish in a few months of construction, while a new detached unit takes longer. Permitting still takes time, so plan for design and plan check before any crew arrives.
The unit has to come from space within the existing house. Owners usually pick one of these:
The garage is the most common choice, and it carries its own planning questions about parking, ceiling height and slab condition. We covered those in detail in our post on garage conversion timelines.
The 500 square foot limit and the efficiency kitchen come from state law, but your city and your property decide the rest. The City of Los Angeles runs plan check and permitting through LADBS, and other cities in the region apply their own versions of the rules.
Owner occupancy is the point owners miss most often. For a junior ADU, the owner generally has to live in the main house to rent out the unit. If you plan to move out and rent both, that changes your options, so settle it first.
Also check your lot. A junior ADU can sit alongside a full ADU on a single-family lot, which gives some owners a path to add both over time. Our guide to stacking two ADUs on one LA lot explains when that works.
Plan for the exterior door early. A junior ADU needs its own entrance, and where that door lands affects the walkway, the lighting, the drainage and how the unit relates to the front of the house. Neighbors notice a new door on a street-facing wall, so a side or rear location often makes the cleaner choice.
Fire separation and egress also shape the layout. The unit sits inside a house that was designed as one dwelling, and the plans need to show how the two spaces stay separate while the owner keeps access to both. Your design team should settle these details before drawings go to the city, since a correction cycle at plan check costs weeks.
Interior conversions look simple on paper, and that is where owners get surprised. Walls you plan to open may carry load. A garage slab may sit lower than the house floor. Old wiring and a small electrical service often cannot support a kitchen and a mini-split. Water and sewer lines may need new routing, and the electrical service may need an upgrade coordinated with LADWP.
A structural engineer reviews each of those before the drawings go to the city. We keep a licensed engineer in-house, so the person who checks your framing and the people who build it work from the same plans. That avoids the gap that opens when design, engineering and construction are three separate companies, each with its own scope and its own schedule.
A junior ADU costs less than a new detached unit because you are not building a new structure. The savings come from skipping the foundation, the exterior framing and the roof, and from sharing utilities that already exist.
We do not quote a number in a blog post, because the real figure depends on the condition of the space, the electrical and plumbing work and the finishes you choose. What we can promise is the way we price it: a fixed price from day one with no subject-to-change clauses, so the number you sign is the number you pay.
The return side is just as property-specific. Rent depends on the neighborhood, the unit's layout and your own use of it. If rental income is the goal, our ADU rental income calculator lets you model it before you build.
Start with a feasibility review. Someone has to look at the space, confirm what your city allows and tell you whether the conversion makes sense before you pay for drawings. Since 1987, SKS has handled design, engineering, permits, construction and city sign-off under one contract, and a junior ADU is a good fit for that approach because the scope is tight and the decisions are few.
If you are weighing a junior ADU against a larger build, we will walk through both with you and show where each one pays off. Book your complimentary consultation through our contact page or call (818) 855-1181, and you will speak directly with the owners.
info@sksconstruction.comCA CSLB License #AB720390(818) 855-1181