5D Building Takes Construction Into a New Dimension

Broad Sustainable Building's new modular technology is built to last.

Broad building sample


Broad Sustainable Building calls their latest system the "5D Building" because 3 dimensions weren't enough. Treehugger readers got a taste of it earlier this year when Broad built a "Restackable COVID Hospital" in South Korea, assembling it in just two days; Daniel Zhang, executive director of the 5D Building subsidiary of Broad, tells Treehugger that it has already been unstacked, moved and restacked in a different location.

The 5D system addresses many of the issues that have faced prefabricated buildings of different kinds:

  • Modular prefabricated buildings have the advantage that everything is done in the factory environment, but they are often too big to ship economically, which limits the distance they can travel from the factory, and it really is a big 3-dimensional box of air.
  • Panelized prefabricated buildings are more efficient to transport because all the 2D panels can be stacked together, but require a lot of work on-site putting all the pieces together.
  • Shipping container buildings rely on the fabulously efficient worldwide transportation network that has globalized manufacturing, but shipping containers were designed for freight, not people, and the interior dimensions make lousy living spaces.

The 5D Building (B5D) combines the virtues of all three prefab concepts. It leaves the factory in Changsha, folded up to the size of a standard 40-foot shipping container, which can be moved inexpensively by truck, train, and ship to anywhere in the world, not a minor issue when the factory is in the middle of China. But it is not an empty box; 2D flat panels fold down to create open space, while the box holds the 3D expensive-to-build components like mechanical systems, bathrooms, and kitchens. Broad explains in greater detail:

B5D system modules
"Each such module, on arrival at the location, is then unfolded lengthwise to twice its width. Total construction area is 60 square meters, with a 3 m standard floor height and 2.83 m indoor clear height. At present, there are about 20 combinations of standard room modules and elevator modules. In addition, balcony, exterior wall, and windows treatments are also selectable."
Acorn folding house plan
Carl Koch

This is not a new idea; Carl Koch proposed it for his Acorn House in 1946, which was to be an affordable, transportable, and very lightweight house. The core of the kitchen and bathroom is built in 3D in the middle, and then the floors and walls of the bigger empty rooms fold out from the sides and end.

Acorn House Wall System
Carl Koch

To keep the house really lightweight, Koch proposed a paper and cardboard wall and floor system, writing in his autobiography, "At Home With Tomorrow," that "you get what is known as a stressed-skin construction, which has strength and insulative ability out of all proportion to its weight and at a theoretically very low cost."

Bcore slab
Broad Sustainable Building

Remarkably, that's exactly what Broad has done with its BCore panels, for exactly the same reasons, albeit with stainless steel instead of cardboard. (More on the panel on Treehugger here.) Broad notes:

"In terms of environmental protection and energy-saving, the floor of a 5D building is made of 15cm [6"] thick BCore panel, filled with rock wool for sound insulation and heat preservation. Its weight is only 1/10 the weight of the same volume of concrete, but the strength is 5 times that of structural steel."
Single module on its own

The panels are insulated with 8 inches of rock wool, and the large windows are quadruple-glazed; smaller ones are triple-glazed. Even though the modules are not shipping containers, they have standard corner castings like shipping containers that are a nightmare of thermal bridges. Zhang, whose father Zhang Yue founded Broad, tells Treehugger that these are wrapped in vacuum insulating panels to maintain a continuous wrap of insulation. "This combination was designed in order to achieve better energy-saving and heat preservation, delivering an instant passive house." Broad continues:

"Floors, walls, windows, and glass; electrical and mechanical equipment; AC and DC power, lighting, water supply, and drainage; as well as sanitary facilities, are all completed in the factory before transport. Because 95% of the producer is preassembled, there is minimal work to be done on site. After bolts are tightly connected, and water supply and drainage among modules and electricity are ready, the structure can be occupied immediately."
Broad Unit

Stainless steel is not the most environmentally benign material, but Zhang tells Treehugger that they are not using very much of it because the structure is so efficient. Zhang previously told Treehugger that "the carbon intensity is about 3.6 tons of CO2 per ton of steel; however, when in the future our source takes in recycled stainless steel, our emissions would be 1.5 tons of CO2 per ton of steel." And at 90 kilograms per square meter, a ton of it goes a very long way. It is also more fire-resistant than normal steel, and is additionally protected by fireproofing underneath.

Normally, one would do a life-cycle analysis to figure out the true carbon footprint of a material but this is hard to do when the material lasts essentially forever; Broad projects a lifespan of 4,000 years for the panels.

A Forever Building

open building
John Habraken via Unity Homes

This brings us around to the most interesting aspects of the project. Back in the sixties, John Habraken wrote about how different components of buildings have different lifespans; a site lasts forever, a structure for hundreds of years, services like plumbing and wiring and space planning far shorter, and stuff might last a matter of months. Some builders, like Tedd Benson of Unity Homes, learned from this and design their buildings in what they call layers, "disentangling" the mechanical systems from the structure.

mechanical systems

The B5D designs are disentangled; you can have the almost forever structure, and upgrade the services inside as required. But you can go even further with what Zhang and Broad call "disestablishment" – "5D buildings can be completely folded up and rebuilt in another location, turning the concept of housing from fixed real estate into 'movable property.'" Essentially, you can take the building apart and move it somewhere else.

Housing units stacked and moved
Corb V2.0. Austin Maynard Architects

This is something that Treehugger has been discussing for a long time in posts like "It's Time for Another Look at Plug-In Housing," which included Andrew Maynard's Corb V2.0, where housing units could be rearranged at will.

It's not so simple as that with the B5D system, you are not going to be moving units just because of a party. However, there are many properties that might be vacant for a couple of years where this might work as a rental building in the short term, perhaps for all those workers, teachers, and nurses who can't afford to live in many expensive cities. You could build them on school parking lots or for that matter, they are so light you could probably plop them on roofs. Because the building can be separated from the land, it dramatically changes the economics of real estate.

Or, if the water is rising because of climate change, you can move the whole building inland. This would be an excellent idea for condos in Miami.

kit of parts for building

Broad concludes: "In the future, we believe it will become the mainstream of our communities, and cities because it is more environmentally friendly, more resource-saving, and [provides] more safety."

But the future is not so far away; Broad is taking orders as of January 2021, for delivery anywhere in the world.

This Could Be Big.

Interior final

As an architect with an interest in prefabrication and transportable housing since university (and having designed something like this decades ago) I am endlessly fascinated by the work of Zhang Yue and Broad Sustainable Building. They are constantly developing new ideas and they don't wait around, they just go ahead and build them and show them to the world, with each iteration getting more interesting and sophisticated.

They are not without issues and problems and things one can complain about, from aesthetics to the worries I have in this building about the thermal envelope. I am still not entirely convinced about stainless steel as a building material; it is made with lots of nickel, which right now is in serious demand because it goes into batteries too, and is not a renewable resource.

On the other hand, what we have here is in a sense a renewable building; the structure can last forever, and it never has to be demolished, just disestablished. it is a different way of thinking about what a building is.

It's also fast, affordable, noncombustible, and transportable. It can go anywhere in a hurry. It is by no means perfect, but it addresses so many of the historic problems of prefabrication and some of the serious problems in the housing industry. This could be big.

This is a big tower
This could be big. B5D

Website is coming soon with more information at Broad Sustainable Building.