ADU Permitting Basics (Part 1): Where You Can Build, Lot Eligibility, and Living Rules

By: Adrienne Norris

Adding an accessory dwelling unit (ADU) can be a smart way to create a guest space, a separate office, or a rental that supports extra income. Before diving into designs or exploring prefab options like the Summit Series, it helps to understand the main permitting and planning factors that come with building an ADU.

This article is Part 1 of a two-part mini-series on ADU permitting and early-stage planning. Here, we cover where ADUs are typically allowed, how to evaluate whether your property qualifies, and what to know about living in an ADU full time. These are the core building blocks for anyone exploring this type of home upgrade.

Which States Allow ADUs?

ADUs have surged in popularity, and many states have updated rules to make them easier to build. California, Oregon, Washington, and Vermont are often cited as leaders, using legislation to support housing supply and multigenerational living.

Still, the details vary widely. Some states set broad statewide standards and simplified permitting paths. Others leave the decision to cities and counties, so rules can change significantly from one area to the next.

Before you move forward, confirm the following with your city or county planning office:

  • Whether ADUs are allowed in your zoning district
  • The types permitted (attached vs. detached, studio vs. multi-room, and similar)
  • Setback, height, and square-footage limits
  • Parking requirements or constraints

Many municipalities also publish online ADU guides or permit portals that speed up research. You can also use our online search tool to get quick, location-based information.

Can Your Property Support an ADU?

Even in ADU-friendly regions, not every lot meets the requirements for a second unit. Eligibility often depends on factors like lot size, existing structures, and access to utilities.

Key questions to consider include:

  • Is the property zoned for residential use?
  • Does the lot meet minimum size rules?
  • Is there room to comply with setbacks and height restrictions?
  • If you have an HOA, does it allow ADUs?

It is also worth thinking through utility connections, driveway access, and how the ADU affects day-to-day function of the property.

Note: If you want to keep going, Part 2 covers the permit process in more detail, including permit types and how approvals typically work.

Can an ADU Be Your Primary Residence?

Often, yes, but it depends on local regulations. In many areas, ADUs can be used as a primary home, a long-term rental, or a vacation-style stay. Some jurisdictions allow you to live in the ADU and rent the main home, while other places require owner-occupancy in one of the units.

Ask your local planning department about scenarios like:

  • Living in the ADU while renting the main home
  • Housing family members, including aging parents or adult children
  • Renting short-term or long-term (and any limitations on Airbnb or VRBO)

Knowing these rules early helps you plan a space that fits your goals while staying aligned with local housing requirements.

 

What Comes Next in Your ADU Planning Journey

With the right information upfront, building an ADU can feel far less overwhelming.

Start by confirming what is allowed where you live, validating that your lot qualifies, thinking through how you will use the space, and estimating overall cost. From there, you can step into permitting with more clarity and confidence.

Ready for the next step? Part 2 breaks down permits, approvals, and what to expect as you move toward a build.