Watch Broad Build a Four Story Apartment Building Overnight

And we were impressed when Broad built hotels in a week.

Broad Sustainable Building has done amazing things in construction, building hotels in a week and the world's tallest prefab in months. But even that was too slow for Chairman Zhang Yue, so the company has developed a new product, the Bcore CTS slab. And they have made a great new video, showing a building being put together overnight.

CTS slab is a strong structural material that consists of two steel panels clipped with thin-wall core tubes, welded with copper brazing. The gap between the tubes is filled with rock wool for thermal insulation. Applied to a building structure, CTS slab is 10X lighter than concrete, fundamentally eradicating earthquake threat. Anti-corrosion performance of CTS slab is 100 times more effective than that of carbon steel. The life span is almost limitless.

© BSB/ Building set up at Foxconn

It also goes together just about instantly; it is like building with a Charles Eames card building set. Broad has built both an instant building and an instant elevated highway test section at Broad Town in Changsha.

The challenge was figuring out how to weld it all together:

© BSB/ cutaway of CTS slab

The aviation industry is used to employing stainless steel honeycomb slabs as the shell of space capsules, but it is not affordable even for aircraft due to its extremely high cost. In 2016 BROAD invented the core tubular slab structure in which the honeycomb is replaced by round tubes, making low cost honeycomb slab production a reality. From 2016 to 2018, with an input of 1000+ staff and 110 disastrous failures, BROAD has invented the globally unique hot air copper brazing furnace, realizing low-cost massive production of CTS slab.

© BSB/ pile of slabs before assembly

It is interesting stuff, because it is so strong and so light. TreeHugger had a lot of questions and chatted with Daniel Zhang of Broad. I was particularly worried about thermal bridging and the embodied energy.

© BSB/ assembly at Foxconn

The thermal bridging exists, yet the walls of the tubing are so thin, so so far it performs close to structural bearing wood beams, overall. Embodied energy as according to calculations because it is stainless, the life span and recyclability, making the embodied energy over the long term lower than wood, steel, concrete. The strength comes from the higher weight to strength ratio, the little tubes does all the shear wall, compression work.

© BSB/ Slabs being placed

Embodied energy is a function how much CO2 is emitted when the product is made, but also of how long a building or the material lasts, and stainless steel lasts a very long time. Currently, it is made out of virgin stainless steel, because they cannot find enough recycled.

© Broad Sustainable Building/ Finished Interior

"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." Of course, a ton of stainless steel put together like this gives you a lot more building than a ton of concrete. I have asked for the weight per square meter to figure out what its real carbon footprint is. As Daniel notes, durability is important.

In essence, it is an architected material, which makes it last longer, so we can reducing mining for resources, there is a calculation, iron that is rusted away on the surface of earth totally is more than we extract each year.

© BSB/ interior of finished space

What about fireproofing?

We have two solutions, one is a hard shell fire proofing board made to extend the fire compromising time to 3 hours before reaching 1000 degrees, and a second is a fire proofing spray for the service areas of the building, where aesthetic isn’t as demanding. However, a benefit of stainless steel core compared to concrete is that after strong fire you can use water to put it out, whereas concrete would brittle and collapse. And as compared to steel, stainless steel’s melting point (softening temp )is 1,200 C, compared to carbon steel at 700 C, so that extends the fire proofing time.

© BSB/ Finished kitchen

Currently, the slabs are 12m (40 feet) by 2m (6.56 feet) and 6 inches deep, and are used as both walls and floors. Because the Bcore CTS slabs are so light and last so long, Broad has high hopes that it can become a prominent sustainable building product. Daniel tells TreeHugger:

The new structure system brought forth by Bcore is going to greatly simplify architects' and engineers' understanding to integrate building systems. In the future we hope when everyone can "speak" Bcore as a shared language of design, so far the laboratory test for Bcore is really promising. I believe the vision is once more people adopt this new structure method, the communication can lead to designing better built environment.

© Broad Sustainable Building/ elevated highway

It will be interesting to see how this plays out. I am not crazy about elevated highways that go up in days and last for generations, but affordable, instant buildings are another story altogether. Imagine how this changes things; you have a building that weighs almost nothing so it doesn't need much in the way of foundations. Being flatpack, the whole thing comes in on a couple of flatbed trucks. Broad is rather proud of the way they throw a lot of workers and big lights at a project and build so quickly, but you don't need a lot of staff with big panels like this (which is why CLT buildings go together so quickly), so even in North America, you could have a building complete in a couple of days. And you don't even have to worry about a bit of rain.

© BSB/ highway and building in Broad Town