Off-site construction: where it pays and where it does not

Repetition is the condition

A unit that repeats twenty times justifies a mould and a production line. A unit that repeats twice justifies neither, however much better the off-site quality is.

What is actually shortened

The time saved is not casting time but waiting time: off-site fabrication runs in parallel with foundation work instead of following it.

The constraints that get forgotten

• Road width and bridge clearance along the transport route
• Crane capacity on site
• Installation sequence, which becomes a delivery plan rather than a schedule