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 U.S. buyers care
ADU demand is not only a California story. Homeowners, investors, and builders across the United States compare backyard housing, guest units, rental suites, and modular housing packages, but every project still has its own state, city, utility, and site conditions.
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 an invented final price.