Thinking About an ADU? Six Things to Check Before Anyone Draws a Line

Accessory dwelling units, often called ADUs or granny flats, have become one of the most talked-about ways to add living space in California. The excitement is justified, but the property decides what is actually possible, so check these six things first.

1. What type of ADU fits your lot?

ADUs come in several forms: a detached backyard unit, an attached addition, a conversion of an existing garage or other space, or a junior ADU created within the walls of an existing home. Each type is treated differently by the rules, and each suits different lots and budgets. Understanding the options before you commit to an idea saves a lot of redesign.

2. What do state law and your city allow?

California has passed a series of state laws intended to make ADUs easier to build, and cities may not go below certain baseline allowances. Cities can still set their own standards within those limits, and the details change as laws are updated. Always confirm the current rules for your specific address with your city's planning department or an architect who works with them regularly.

3. What is on your property already?

Existing structures, mature trees, easements, utility lines, slopes and the location of the main house all affect where a unit can go. A current survey is one of the most useful documents you can bring to a first design meeting. If you do not have one, expect to be asked for one.

4. How will utilities connect?

Water, sewer, electrical service and sometimes fire access all need to reach the new unit. The distance and condition of existing connections can influence the budget and the location of the unit more than the design itself. Ask early what upgrades may be required.

5. Is your property subject to additional layers of review?

Hillside areas, fire hazard zones, historic districts, coastal zones and homeowners associations can each add requirements. These do not necessarily rule out an ADU, but they can change what is feasible and how long the process takes.

6. What is the unit for?

Family housing, a rental, a home office, or a flexible space that serves several purposes over the years: the answer shapes the layout, the privacy between buildings, the entrances and the services. If you may rent it out, check the rules that apply to renting ADUs in your city as well.

The most expensive ADU is the one designed before anyone checked the lot.

A short feasibility conversation before design can tell you what is possible on your property and what questions the city is likely to ask. Related reading: when a remodel needs a permit and remodel or rebuild: the questions that settle it.

General information only, not legal, engineering or code advice. Rules differ by city and change over time, so confirm the details for your property with your local building and planning departments and with qualified professionals.