Define "prefab". Is it a building built in a factory and attached to the existing house; or is it 2x wall panels constructed in a factory and assembled on site then completed like stick construction would be?

A neighbor’s son worked for a pre fab wall framing/roofing truss company in Tracy, CA.

The contractor places the order, a couple of weeks later a truck shows up at the job site. Price of fuel/transportation is low. There are more moving parts to offsite building/transportation. A train car load of lumber costs less than buying lumber from the local yard. Non union labor costs what it costs, it is easier to work in a building, than in the field.

From what I understand it’s like they build in factory and bring it to our house and attach. We can have as much “done” as we want. But I have been told it’s more cost efficient than them framing from lumber yard conventional way. And it’s stronger. I don’t know... would love to know people’s experience.

https://www.kbsbuildersinc.com/the-modular-advantage/