So, I don't understand how this can be cheaper. I just saw a neighbor put together a house out of large bricks with six guys in two days. Doing the same using this method seems like it would have been more expensive. Is this an economies-of-scale thing or what?
Edit: Here's a second video [1] where they use concrete. It says that factory can makes enough for 60 houses per year. It also says, at the end, that it's not cheaper but faster and "easier on the nerves" for the builders.
From what I've heard from friends who build, it's less about having six guys show up and two days later there's a house, it's about what happens when they're busy and don't show up for three months while the cost of materials goes through the roof and you're stuck renting and/or paying two mortgages.
If you can engineer out some of the potential delays that can take a huge amount off the overall cost.
In the end it's about the same cost (for the same quality).
Also prefab houses have a lead time of about 6 month.
But once the on site build has started it's fast and those elements come with electrics, water piping and (sometimes) windows preinstalled. They just need to be connected.
You basically have the choice between the classic building methods with an architect and contractors, or an All-in-One Firm that has it's own contractors and almost always uses the prefab model. The later also is way less hassle for the once-in-a-lifetime home builder, usually.
Usually it's done with wood but there are also factories that build prefab houses with bricks.
https://www.youtube.com/watch?v=QJIDjdFTVW8