by William McCallion, AIA, LEED AP, Manager of Quality Control & Training
Has the time of high-rise prefabrication finally arrived?
Why has the construction industry been so late to the prefabrication party? The automotive, aerospace and even shipbuilding industries have been doing it for decades by utilizing sophisticated 3-D computer modeling to further perfect their design and assembly. Of course, the overriding advantage in these industries is the size of the companies and the number of units they produce. Unlike other industries, building construction tends to be more fragmented with few companies reaching the national or international market; most are local or regional.
However, the introduction of BIM (Building Information Modeling) and IPD (Integrated Project Delivery) in design are providing an opportunity for change. Knowing exactly what a building’s design is before putting a shovel in the ground provides enormous advantages which also enables the manufacture of components prior to erection whereas in traditional design many issues are worked out in the field as the project progresses leading to lost time and a greater potential for Change Orders.
Prefabrication is not new, but it has been limited and most of the market is for modular homes. Other successful areas have been the manufacture of components such as precast elements like T-Beams in garage structure or precast exterior wall panels. Exterior wall panels have become quite advanced and can now be shipped with face brick and windows installed. However, the holy grail of an entirely prefabricated large scale building has only rarely been achieved. This is changing.
First, why build utilizing prefabrication? Some of the reasons are:
It may seem intuitive that prefab saves cost. This has not been borne out at this time, primarily due to the limited scale of the projects that have utilized it.
Prefab is not without its problems. Gaining height is problematic as the modules are usually self-supporting, the lower one bearing the weight of the next one. Some type of frame may need to be erected to permit higher structures. The foundation must be constructed to exacting standards since there is no ability to alter a prefabricated module once it gets to the job site. In addition, since the prefab facility is often in a different jurisdiction than the site, perhaps across state lines, there could be code issues. The path of travel of the modules must be precisely calculated and the width of the modules’ trailers must be permitted by the jurisdiction they travel through. And finally, union requirements also need to be considered.
Prefabrication lends itself toward repetitive components and is ideal for hospitals, dormitories and residential projects. One of the links below contains a video of a modular hospital being built from start to finish.
So, what is the current state of prefabrication? It is getting pretty interesting in New York City. A recently completed mid-rise residential building is being completed in the upper part of Manhattan.
The tallest prefabricated building in the USA is under construction in Brooklyn. The first modules are being set at the 32-story residential building at the Atlantic Yards Development. (Merritt & Harris provided consulting services for the Barclay Center at Atlantic Yards.)
In addition the first “micro” unit building in NYC will be constructed on E. 27th Street in Manhattan and will utilize prefabricated modules.
And the most mind-blowing achievement might be the planned Sun City tower in China which will rise to 202 stories making it the tallest building of any kind. Details about the prefabrication methods are sketchy but some photos have leaked out purporting to show the prefabrication in progress.