Conversion or New Construction: What Type of ADU is Right for Me?

Legislation was passed in California in 2017 that made permitting Accessory dwelling units (ADUs) much easier than it had been previously in response to the housing crisis. The idea was to help make the most of our current infrastructure by creating new homes without upending neighborhoods or redeveloping properties. In San Diego, ADUs can be built on property that is zoned for either single-family or multi-family residences (depending on the local regulations). It’s best to check with the City before building on the land. Additionally, to obtain a permit for a lot, it must be free of code violations.

Accessory dwelling unit, or ADU, is something of a broad term, as there are several different kinds of ADUs, but for the most part, you just need to know that some are attached to an existing building and others sit on their own plot. We’re going to focus on the cost to convert a garage to an ADU and on the logistics of building a detached ADU, which in some cases are units converted from existing garages and sheds and in others are built from scratch.



A garage conversion is typically quicker to permit, and the construction timeline is much faster than building a new unit from scratch. Many garage conversion ADUs can be designed, permitted, and built within 6-8 months. That is a really quick way to add liveable space to your property.

Taking into account all of the costs associated with architecture, permitting, working with a contractor to do site prep and construction an ADU garage conversion can cost you between $80,000 and $150,000 — and sometimes even more. 

A garage conversion is a good option if you don’t want to lose backyard space or if your goal is to keep this new living space small. Most one-car garages are between 162 and 384 sq. ft. and would technically count as a junior ADU (JADU). On the other hand, while a garage conversion ADU is an economical use of your space, you’re losing space to store your vehicles and other storage items. 



New Construction

A new construction ADU is a small home on your residential property. The ADU is not the main house, of course, and it may or may not be connected to the main house.  

The size of an ADU varies. At the smallest, an ADU might measure 600 square feet, the minimum size is 150 sq. ft. but we can’t imagine a space that size would be too desirable if you’re hoping to rent it out. Bigger ones could be 1,200 square feet or over. Here in San Diego, detached ADUs can be built up to 1,200 square feet, as long as they are less than 16 feet high and respect 4 foot rear and side yard setbacks. Considering that the average apartment is 800 square feet, you’d have as much room in an ADU as you would in a typical apartment.

An ADU is designed as its own house. It should have entry and exit doors, a living room, a bathroom (possibly more than one), and a kitchen. This way, the residents in the ADU do not have to come into the main house (or vice-versa) to use the bathroom or kitchen. Structures like these are desirable for vacation rentals, income properties, and private residences for family, friends, or other independent adults. If you have the space to build a new construction ADU, they can be a fantastic way to increase the value of your home. That being said, building another self-sufficient home on your property is an investment of both time and money. 



We encourage you to use our ADU Investment Cost Calculator to not only estimate the costs of building an ADU but to see the immediate and long-term benefits in terms of return on investment and home value.