Published Sep 23, 2025. Updated Sep 29, 2025. Written by John Phillips.
This is the fifth installment in a six-part monthly series about Accessory Dwelling Units, or ADUs. ADUs are small separate living spaces on an existing residential lot. They are also called mini homes, granny flats, or in-law suites.
The article focuses on modular construction. In modular construction, buildings are assembled in a manufacturing plant, delivered on trucks, and set in place with a crane. ADUs are well suited to this method because they are often only one or two modules.
ADUs are often detached and compact. That makes them easier to build as modules, transport, and install. The modular building process can run at the same time as site work, including foundation work and utilities.
The article says the purchasing experience for a modular unit can feel more like buying a car. A buyer chooses a model, finishes, and accessories. The unit is then delivered and installed on a foundation.
The article cautions buyers to choose the manufacturer carefully and to use a reputable general contractor for site work and installation.
An ADU is a small independent residential unit on the same lot as a primary home. It can be attached or detached.
They are often only one or two modules, which makes factory construction, transport, and crane installation simpler.
The article says it can be up to 40% faster than traditional stick-built construction.
The article says construction costs can be 20% less than traditional building techniques.
They are often used for aging parents or young adult children so families can live close together while keeping separate living spaces.