The simple definition
An ADU is an accessory dwelling unit: a smaller independent residence added to a property that already has a primary home. Buyers use ADUs for rental income, family housing, guest space, caregiver space, aging-in-place plans, or a more flexible property strategy.
Why California buyers care
California has encouraged ADUs because they can add housing without requiring a completely new subdivision. That does not make every project automatic. The state framework helps, but the actual project still has a property, a jurisdiction, a utility setup, and a site condition.
The terms people confuse
Prefab, modular, factory-built, panelized, kit, manufactured, and site-built are not the same thing. A buyer should ask what is manufactured in a controlled setting, what arrives on site, who installs it, and what the local authority still reviews.
Why cost gets confusing
Many ADU conversations start with a product price or a rough square-foot number. That can be useful, but it is not enough. The installed budget also needs freight, setting, foundation, utilities, permit fees, finish allowances, site restoration, and contingency.
How ADU Cost helps
ADU Cost is built as an education and quote-intelligence site. It explains the product packet, organizes the cost stack, and makes unknowns visible so a buyer can move toward a real quote without accepting a fake final price.