The allure of building indoors in a controlled environment instead of in the mud, muck, and maelstrom of a conventional site has made prefabrication a strong candidate for the future of construction for architects, engineers, and construction futurists. But time and again, the revolutionary potential of the approach has failed to materialize. The barriers to industrial building — the decentralized nature of the industry and the limited number of employers in a position to make long-term investments, the complications of transportation, and the uncertainty about demand for the product — ensure that modular building will remain a stable but relatively small percentage of total construction spending.