A guide to accessory dwelling unit and prefab home builders in the US. Compare prefab ADU companies, backyard-office builders, modular home manufacturers, and custom ADU contractors, with a plain summary of what each builds, how the permitting and install work, and which states they serve.

An accessory dwelling unit is the small second home you put on a lot you already own: a backyard cottage, a converted garage, an in-law suite, or a prefab studio for a home office. The rules loosened across much of the US over the last few years, and a whole industry grew up to build them. The trouble is that "ADU builder" now covers everything from a factory that cranes a finished house onto a foundation in a day to a general contractor who frames it on site over months. ADU Build Hub sorts them by how they actually build, so you can shop by the kind of unit you want and the way you want it done.

The right builder depends on your project. A prefab company sells a finished, permit-ready model with fixed pricing and a fast install, which suits a standard backyard unit on a clear lot. A modular manufacturer gives you more floor plans and finishes for a larger or multi-unit build. A custom ADU contractor makes sense when the site is tight, the design is bespoke, or you are converting existing space. And a growing set of firms just build backyard offices and studios. Each listing explains what the company builds, how the permitting and installation work, roughly how long it takes, and which states it serves.

We favor builders that own the process end to end and are clear about all-in pricing, and we say where a company operates so you are not reading about a service that does not reach your state. Every builder gets its own summary rather than a restated brochure. The established builders come first.