That’s because they won’t be needed. One primary reason 3D printed homes are less expensive is because so much less labor is involved. Fewer people to pay.
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3D printing at scale will bring huge change to many industries including “construction”. We are already seeing this in the machining industry where replacement or repair parts can be printed immediately.
It’s a long way from perfect but its getting better by the month and history will most certainly recognize this as one of the biggest technological advances of this century.