Accessory Dwelling Units

In the past few months, we have started receiving many calls for new or converted Accessory Dwelling Units, or ADU’s. More and more homeowners want a separate apartment on their property where guests can stay, where an aging parent can live independently, and – in a few cases – where the family can live comfortably while we remodel their main house!

New Guidelines for Accessory Dwelling Units

In response to California’s housing shortage, recently adopted legislation promotes the development of Accessory Dwelling Units, or ADU’s. Going into effect January 1, 2018, these new laws have eased many of the requirements associated with building a secondary dwelling unit that can be used as a guesthouse or for rental income. 

ADU’s are self-contained apartments that include a full kitchen. The unit can be attached to the main house, or it can be a detached structure. Unlike a Detached Accessory Structure (described in my earlier blog about Guesthouses) an ADU may be used for sleeping, and it may be rented out. Only one ADU is permitted on any one lot. 

Where can an ADU be located on the property, and how big can it be?  

Many other websites indicate that a residential lot must be at least 5200 square feet before an ADU is allowed, but this is not true in the city of Sacramento. Here, any size lot may have an ADU. 

There is, however, a limitation on lot coverage, so a smaller lot may have limited space for an ADU. If the property is zoned R-1, then the maximum lot coverage is 40% or 2500 sq. ft., whichever is greater, but in no case can lot coverage exceed 50%. All structures on the property count towards lot coverage, including sheds and covered patios. 

If the ADU is attached to the main house, it cannot exceed 50% of the floor area of the main house. For example, if your house is 1500 sq. ft., than an attached ADU cannot be more than 750 sq. ft. The maximum floor area of any ADU is 1200 sq. ft. 

If the ADU is a detached building, it can be up to 1200 sq. ft. regardless of the size of the main house. And if part of the detached building is a garage, then the area of the garage does not count towards the 1200 sq. ft. limit.

If the ADU is new construction, it must meet all the same design guidelines that are required for the main house. So, for example, the new structure must have the required setback on the side, usually five feet. But if an existing building, such as a garage, is being converted, then no setbacks are required; like so many garages in Sacramento, the building can be right on the side yard or rear yard property line. Any addition to the existing structure, however, would need to meet setback requirements. And always remember to check for utility easements, as described in the blog about Guesthouses. 

Two-Story Accessory Dwelling Units

 Under the guidelines for Detached Accessory Structures, one of the greatest obstacles to converting a garage into living space was the height limitation. The Guesthouse blog describes the 18-foot height limitation that makes two story structures very difficult to design. The new guidelines allow ADU’s to be 35 feet tall, although it would be unusual to need more than 25 feet for a two story building on a slab. 

When a secondary dwelling unit is built above an accessory structure, it must maintain a five foot rear yard setback and, in zone R-1, a five foot side yard setback. 


 The new legislation for secondary dwelling units took away the requirement for additional parking. One off-street parking space is required for the main house, but no additional parking is needed for the ADU. If an existing garage is being converted, then an alternate off-street site must be provided that is at least 10 feet wide and 20 feet long.