Theo Salet, Dean of the Department Built Environment, is the major driver of the Milestone project. "In 2015 we 3D-printed a bridge and in 2021 a one-story house," Salet says. "Now we are showing that we can scale up."

All the knowledge the TU/e has gained with 3D printing since 2015 has been transferred to the companies that will actually build the homes in Bosrijk: concrete manufacturer Saint-Gobain Weber Beamix, architectural firm Houben / Van Mierlo Architects, engineering firm Witteveen+Bos and construction company Van Wijnen.   

Modular and circular

The Municipality of Eindhoven, together with the TU/e, initiated the project and designated the site in Bosrijk. As a knowledge partner, the TU/e helped develop the modular building concept. "We print the inner and outer walls separately from each other, which is different from the first house. At the floor level, the walls are attached to each other," Salet said. "You could say in a follow-up project: we print the interior wall and we use a wooden exterior wall, or vice versa. That's what modular and industrialized circular construction is going to look like." 

The difference from the first 2021 home is significant. "That was like a one-story bunker, with relatively small windows. Now we're going to 3D-print full-fledged homes with tall windows and a modern look."  

Social housing

The fact that 120-square-meter villas roll out of the 3D printer is technically impressive, but also a bit unfortunate, Salet believes. "The Bosrijk neighborhood is a leafy place, the villas fit perfectly there. It is not an environment for social housing. That we now end up with villas of 600.000 euros actually gives a distorted picture, because we want to build cheaper with 3D printing," Salet explains.  

Housing corporation Vesteda was also initially involved but pulled out of the Bosrijk project because the market segment didn't match. The TU/e is currently working with a consortium to develop an alternative modular concept for the cheaper segment, focusing on high construction speed. According to Salet, a grant of 1.5 million euros is already available for this purpose.  

Large mathematical model

One of the major challenges in scaling up house printing is achieving a consistent concrete quality. "Exactly how long do you have to mix cement, sand and water? What happens when the concrete is pumped to the nozzle? We captured that whole 3D printing process in a big mathematical model," Salet explains. "The whole process has been mapped and modulated. Several PhD students worked on that."  

Other housing printing initiatives often work with a loose supporting structure, Salet said. In other cases, the concrete only serves as a mold. "We don't do that, we use the concrete constructively. That's unique. Residential construction is developing like aircraft construction. You go further and further optimizing to use less material. To still build safely, you have to measure more. We do that with smart printing concrete. That's concrete with nanomaterials that allow us to detect cracking at an early stage." Less material means less CO2 emissions for a sector that has a high climate impact.  

Construction of the 3D villas in Bosrijk should start early next year. The homes will be completed in the third quarter of 2025. The villas are already for sale. "There seems to be ample interest in them," Salet said.