Prefab vs Modular vs ADU
These three terms are often used interchangeably, but they describe different things. Understanding the distinction will help you compare builders accurately, avoid confusion in quotes, and choose the right path for your project.
Prefab: A Construction Method
Prefab (short for prefabricated) refers to *how* a building is constructed—not how it’s used. In prefab construction, some or all components of a building are made off-site in a factory, then delivered to the property for installation.
Prefab is an umbrella term that can include:
Prefab construction often offers greater predictability, controlled quality, and shorter timelines, but it does not eliminate site work, permitting, or inspections.
Modular: A Type of Prefab
Modular homes are a specific type of prefab construction. They are built in large, three-dimensional sections (called modules) inside a factory and then transported to the site where they are assembled.
Key characteristics of modular homes:
Modular construction can be efficient, but delivery logistics and site access are important considerations.
ADU: A Use Case, Not a Construction Method
An ADU (Accessory Dwelling Unit) describes *how* a home is used—not how it’s built. An ADU is a secondary residential unit located on the same lot as a primary home.
Because ADUs are regulated differently than primary homes, feasibility is a key early step.
How These Terms Overlap
It’s common for a project to fall into more than one category. For example:
This overlap is why listings and builder descriptions can feel confusing. The key is separating *construction method* from *use case*.
Builders often specialize in specific combinations of these categories. Some focus on ADUs only. Others build modular primary homes. Some offer prefab systems but do not handle ADU permitting.
Understanding these distinctions helps you:
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