Prefab and modular ADUs (companies like Abodu, Cover, Connect Homes, Villa, Boxabl, etc.) are subject to the same California Title 24 PV mandate as site-built detached ADUs once they're permanently installed on a foundation. Here's how to plan the solar portion.
Any prefab or modular ADU that is permanently installed (foundation, sewer, water, electrical) is classified as new construction and triggers Title 24 § 150.1(c)14 PV requirements. Movable tiny homes on wheels (HUD-certified RVs) are NOT subject to Title 24.
Some prefab ADU manufacturers offer factory-installed solar as an upgrade (typically $12K–$20K and not always optimally sized). Buying solar separately from a Title 24 specialist usually saves $3K–$6K and lets you choose better equipment.
If permanently installed on a foundation in California, yes — Title 24 applies. If used as a movable RV, no.
Usually no. Most prefab solar packages are marked up 30–50% above local installer pricing and use entry-level equipment.