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Prefab ADU Guide for (USA) Homeowners: Accessory Dwelling Units Explained



A higher cost of living, limited housing, the undisputed need for a quiet home office or a private pad for visitors—the list of reasons why the modern homeowner doesn’t just want but needs ample living space goes on and on. While we’d all love to escape to the A-Frame cabin of our dreams, secondary dwellings have become an increasingly popular and accessible option when that extra room is simply too hard to find.

Whether you call it a sidekick unit, an in-law suite, granny flat, or simply an ADU, accessory dwelling units are a viable and perhaps, not-so surprisingly, design-focused way to make the most of your space (budget willing of course). If you’re in the market for a prefab ADU, this guide can help you better understand the process, costs, and narrow down the options to score the very best tiny, but mighty, backyard home.

What Is an ADU?

An Accessory Dwelling Unit (ADU) is a self-contained living space that is either inside, attached to, or detached from a single-family home on a single lot. ADUs have a small floor plan (generally from 150 sq ft on up to 1,000 sq ft or more—local regulations may dictate the max size your own backyard can legally host) complete with designated areas for living, sleeping, sanitation, and eating, but don’t go labeling it a tiny home. Even though tiny homes can certainly be ADUs, not all ADUs are tiny homes, because, by definition, an accessory dwelling unit is an additional structure on a single-family property—not an off-site tiny cabin in a remote and beautiful location far, far away, but those are great too.

Compact, modular, and often prefabricated off site, ADUs are most commonly used as a secondary dwelling on the homeowner’s property. They’re ideal as a guesthouse, home office, or as close and convenient housing for family members without having to sacrifice your privacy (or worse, share a bathroom). Depending on your town’s zoning laws, these backyard homes can also be used to generate rental income as a short or long-term rental unit, too. The Airbnb or Vrbo option is especially helpful for generating additional income. Either way, an ADU can and likely will increase your property value.

For these reasons, they’ve become a popular and legal way to add affordable housing units in overcrowded areas—take California, for example, which recently amended its zoning laws and lifted restrictions on ADUs making it easier to create secondary housing units—during a time when home costs are high and living space is hard to come by. However, like any additional structures being added to your property, the size, location, use, and occupancy of an ADU depends entirely on the local laws and building codes, full stop. To find out if it’s legal to build an ADU on your property, and how you’re allowed to use it, check the county and city zoning laws or take a trip to the municipal clerk’s office for more information. If your jurisdiction doesn’t have specific laws for ADUs, follow the state regulations for guidance. This process will be tedious and perhaps even frustrating at times, as most counties are slow to adapt. Good luck!