ADU Questions · 2026
What Is a Detached ADU?
A detached ADU is a fully separate, freestanding structure built on the same lot as a primary residence, with its own walls, roof, foundation, entrance, kitchen, and bathroom. It isn’t attached to the main house in any way, it’s a real second home that happens to share your property. That’s the type of accessory dwelling unit most people picture when they hear “ADU,” and it’s the only type Framework First builds.
The short version: A detached ADU stands entirely on its own, separate from the main house. That’s different from an attached ADU, which is built onto or connected to the primary home, and a JADU, which is created within the primary home’s existing walls.
Detached ADU vs. attached ADU vs. JADU
All three are legal ways to add a second living space to a single-family lot under California ADU law, but they’re built very differently.
| Detached ADU | Attached ADU | JADU | |
|---|---|---|---|
| Structure | Freestanding, separate building | Built onto or connected to the main home | Created inside the main home’s existing walls |
| Max size | Up to 1,200 sq ft (state cap) | Up to 1,200 sq ft, sometimes tied to a percentage of the main home | Up to 500 sq ft |
| Max height | At least 16 ft allowed everywhere (up to 18 to 20 ft near transit) | Up to 25 ft | Within the existing home |
| Kitchen | Full kitchen | Full kitchen | Efficiency kitchen allowed |
| Bathroom | Its own, always | Its own | Can share with the main home |
| Owner-occupancy | Not required | Not required | Required only if it shares a bathroom with the main home |
A detached ADU is a standalone building, full stop. An attached ADU shares at least one wall or connecting structure with the primary house. A JADU isn’t a new building at all, it’s a smaller unit carved out of space the main house already has, like a bedroom with its own entrance and a small cooking setup. For the full breakdown of that last comparison, see JADU vs. ADU.
Why most homeowners choose a detached ADU
A detached ADU gives you the most privacy, the most flexibility, and the most resale value of the three options. Because it’s fully independent, it works equally well as a rental, a space for aging parents, an adult child’s first home, or a guest house, without anyone sharing walls with the main house. It also doesn’t require you to live on the property, which an attached ADU also avoids but a JADU does not (unless it doesn’t share a bathroom).
Detached also tends to be the simplest path on a typical Salinas-area lot. You’re not modifying the structure of your existing home, which means less disruption to your day-to-day living during construction, and a design that’s built entirely to fit your yard rather than constrained by your home’s existing footprint. For the size math specifically, how big an ADU can be in California walks through the state’s size rules in detail, and ADU setback requirements covers how far it has to sit from your property lines.
How Framework First builds detached ADUs
Every one of Framework First’s 14 models, from 405 to 1,200 square feet, is a detached ADU. About 97% of each home is built inside the company’s Salinas factory, then the finished structure is crane-delivered to your property in a single day and set onto a pre-poured foundation. That factory-first approach is what makes a detached ADU realistic on a normal timeline, typically 4 to 9 months depending on the model, instead of the many extra months a fully site-built structure can take. If you want to compare that build method to a traditional site-built ADU, prefab vs. site-built ADU lays out the differences.
Pricing across the lineup runs $180,000 to $557,000, and that price is built around a permitting budget along with plans, the foundation, the factory build, delivery, utility hookups, appliances, and final inspection. Exact permit costs and any property-specific site work are confirmed in your feasibility study, so you know the real number before you commit. You can browse the full lineup at /models/ or see current pricing at /pricing/.
If you’re still weighing a detached ADU against expanding your existing house instead, ADU vs. home addition compares the two paths directly.
Frequently asked questions
Is a detached ADU the same thing as a “granny flat” or “backyard cottage”?
Yes. “Granny flat,” “backyard cottage,” “in-law unit,” and “detached ADU” all describe the same thing: a separate, standalone home built on the same lot as a primary residence. “Detached ADU” is simply the precise legal term California uses in its housing statutes.
How big can a detached ADU be?
California state law allows a detached ADU up to 1,200 square feet. Some cities cap it lower locally, but state law guarantees every jurisdiction must allow at least an 800 square foot, 16 foot tall detached ADU with 4 foot side and rear setbacks, regardless of local rules. See how big an ADU can be for the full sliding scale.
Does a detached ADU need its own foundation?
Yes. Because it’s a fully independent structure, a detached ADU sits on its own foundation, separate from the main house’s foundation. Framework First pours a dedicated foundation for every home before the factory-built structure is crane-set onto it.
Can I have a detached ADU and a JADU on the same lot?
In many cases, yes. State law generally allows a single-family lot to add one ADU (which can be detached) plus one JADU created within the existing home. Whether your specific lot supports both is exactly the kind of question a feasibility study answers for your property. Start one at /feasibility-study/.
Does a detached ADU cost more than an attached ADU or a JADU?
It depends heavily on size, finishes, site conditions, and the specific project, so there’s no single universal answer. In general, a JADU tends to be the least expensive option because it reuses existing walls and systems, while a detached ADU is a complete standalone home, so it carries the cost of its own foundation, roof, and full set of systems. A feasibility study for your property is the most reliable way to get real numbers instead of a rule of thumb.
Ready to see what a detached ADU looks like on your own lot? Start your feasibility study or browse the model lineup.