An accessory dwelling unit (ADU) is a standalone living space that's smaller than the main home on a property. These units can be used for anything from an in-law suite, to rental income, to housing for family members with disabilities. But before you decide to go ahead and build one on your property, make sure there are no regulations or restrictions against it in your area!

What Is An Accessory Dwelling Unit?

An accessory dwelling unit, or ADU for short, is a second living space that is built on the same property as an existing single-family home. The idea behind this type of housing arrangement is to provide more affordable options in high-cost areas and to help meet the increasing need for multi-generational homes. Accessory dwelling units in California are becoming especially popular to help people bring in more income or to house a family member.

As it stands today, there are about 600 cities across America with zoning restrictions that allow you to build an ADU on your property. It should be noted though that not all municipalities will approve your application if they deem your lot too small or unsuitable for building purposes. HOAs could also restrict your ability to build an ADU on your property. Check with your city and HOA to understand what's allowed for your specific property.

Prefab Accessory Dwelling Unit

Prefab accessory dwelling units are popping up everywhere, with ease of construction and the shorter amount of time required to get it in place increasing their popularity and access. Prefab accessory dwelling units are not always the best choice though, as a stick-built ADU might be a better choice for some properties. Either to match the main home, or for other reasons.

Accessory Dwelling Unit Cost

The average cost of an ADU was $156,000, according to a UC-Berkeley poll. Costs for ADUs do vary, however. In the Bay Area of California, for example, the typical price is between $350,000 and $390,000. Permit costs, materials, and other municipal fees can change the cost considerably.

If you're looking at building an ADU as part of your custom home, check with Bianchi-Tillett Developers to see what it might cost in your greater Sacramento neighborhood.

Problems With Accessory Dwelling Units

Existing Structures 

Because of fire codes, in most areas, the accessory dwelling unit must be attached to the primary home / garage or kept separate by 10 feet. If you don't have the space for this, then adding an ADU can prove to be difficult.

A solution for this is to connect the new ADU to the house or garage with a tiny roof structure, storage space, or small air gap; it should also meet local building codes.


A setback is the minimum distance between a structure and the property lines. These housing regulations are in place for your safety (against fire) as well as access of light and air to you and your neighbors.

Check in your local area to understand the setback requirements so you know how much space you have to work with for your ADU.

Power Lines 

The presence of unsightly power lines through backyards might make ADU placement difficult. If you have electricity wires running across your yard, you're probably fortunate enough to have a utility easement. Many of the county or local offices have strict rules about how close your new building may be to utility easements and high-voltage power.

Parking Issues

One complaint about adding ADUs is adding the number of cars to a property which can lead to parking constraints. In actuality, there's no proof that ADUs cause any sort of parking difficulties. ADUs are tiny residences that are typically designed to house just one or two people, not a large family. An extra car on your street is unlikely to make a significant difference. Yet, some neighbors may try to use this as a reason to complain about the ADU addition.


Adding an ADU to your home plans could be a great thing for your family, either to house an aging family member, or for extra rental income. While there are some challenges with adding an ADU, the benefits could tips the scales in favor or moving forward with one. Check with Bianchi-Tillett Developers as we can help you navigate the building process. Contact us today!

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