About ADUs

If you’re looking for more information about what is considered an ADU, what kinds of ADUs exist, and whether or not you can build one on your property, you’re in the right place.

Below, we’ve answered some of the most frequently asked ADU-related questions and summarized some useful information about the different types of ADUs that are out there.

Types of ADUs:

Here are six of the most common categories of ADU. Click on each image for more information about the characteristics, pros, and cons of each type to see which one would be the best fit for you!


Garage Conversion

Basement Conversion



Above Garage

Frequently Asked Questions

What is considered an accessory unit?

ADUs have many synonyms. An accessory unit is one of them. In my ADU book research, I identified 64 synonyms. An accessory unit is a secondary and architecturally diminutive unit on a property that already has a primary residential unit.

Do I need a permit to build a guest house?

Yes, you need a permit from your local jurisdiction to build habitable living space on your property. If the space is non-habitable, and is under 200 sq ft, then sometimes you do not need a permit. But, in the case of building habitable living space, you’re always required to obtain a building permit.

Does an ADU Require a kitchen?

Yes, ADUs must have a kitchen. In fact, the kitchen is the defining feature of an ADU that differentiates it from other additional habitable living space

Is it legal to build a house or in-law suite in my backyard?

In some jurisdictions, it is legal to build an accessory structure with habitable living space in the backyard. In other jurisdictions, it is not legal to build habitable living space in the backyard. Whether that habitable living space in the backyard can be classified as a house, is another matter. This depends on what your local zoning code says is permissible. In many cases, ADUs will be permissible. In other cases, an ADU may not be allowed, but alternatives such as a guest house or a detached office or bedroom with a bathroom may be allowed.

Does an in law suite or guest house add value?

Yes, an inlaw suite and guest house adds value to a property. The next logical question is, “How much value does an ADU add?”. Unfortunately, it’s impossible to provide a universal answer to this question. The contributory value of additions such as adding an ADU, guest house, or inlaw suite, are difficult to measure. But, professional appraisers will look for sales comparisons on which to base their appraisals-which are their opinion of value of the property based on the sales comparison data that is available to them at the time of their appraisal.

What is considered an illegal apartment?

An illegal apartment is a synonym for an unpermitted ADU, or an informal ADU. This is an additional housing unit that is added to a property without the correct permits. There are subtleties here however. Was the additional structure permitted? Was the interior finished habitable living space permitted? Was it literally just the oven and kitchen sink that weren’t permitted? These subtleties are important to understanding how significant the zoning and building code violations actually are.

Are ADUs allowed in my neighborhood?

In 2019, California passed a series of bills to make it easier for homeowners to build ADUs. Major changes to zoning regulations, permit requirements and developmental standards went into effect on January 1st, 2020, superseding previously restrictive local regulations. While zoning, regulations and fees vary by municipality, the recent state laws say that ADUs can be built on property zoned for single-family and multi-family use.

Why are ADUs becoming more popular?

See if an ADU fits on your property!

This very handy online tool lets you see what size of ADU will work on your lot. It’s currently only available in select Bay Area city, but is rolling out to the whole state of California very soon!

Have a Question?

If you have unanswered questions or want to join our community of ADU knowledge-seekers, reach out to us using the form below!