What’s the difference between a site-built and a manufactured ADU?

A traditionally constructed site-built ADU is designed and built specifically to your preferences and property. This option allows for a lot of customization and smaller changes to be made throughout the construction process.

A manufactured or prefab ADU is built partially or mostly in a factory, then shipped to your site to be put together. This option requires a lot less of your builder since so much is done off-site, and usually includes laying the foundation, on-site assembly, utility hookups, and overseeing inspections. Manufactured and prefab ADUs often save time because the site can be prepared while the home is being constructed, but they also typically offer less customization.

It is often surprising for people to learn that manufactured or prefab ADUs often cost the same as traditionally constructed ADUs, although some companies do offer lower-cost options.

Types of prefab

Panelized: Homes constructed from two-dimensional, pre-built sections that are assembled on-site.

Manufactured (Mobile Homes): Built off-site like prefab but regulated by federal building code and usually more affordable. The construction standards are lower for these, and they usually do not hold up as well.