But the most important test—whether the printer could print a house on the site—went well. The printer works by squirting a concrete mixture in layers to build floors and walls. Software monitors the weather conditions, and the machine can adjust the mixture. “In the morning it might be drier, and then late in the afternoon, maybe it’s more humid, and then you’ll adjust that mixture a little bit in accordance to that that you get the viscosity that you need in order to have the same print quality throughout the day,” says New Story cofounder Alexandria Lafci.

The team can use an app to make slight adjustments to the blueprint on site, but the printing process is essentially autonomous. To make it even more efficient, it’s possible to print multiple houses simultaneously. The first two homes were printed at the same time, in a total of 24 hours over multiple days, because the team wanted to work only in daylight hours; in the future, they hope to run the machine for longer periods, making it even faster. New Story has partnered with a local nonprofit, Echale a Tu Casa, to finish the parts of the homes that can’t be 3D-printed, providing jobs to local construction workers.

This looks really cool, but I think the neatest part is how they decided to field test it in a jungle near a seismic zone. The 50 families who are getting these homes (for free!) will be moving from corrugated tin shacks without plumbing.

Some families toured the first two houses last week, noting how the new homes would stay dry in heavy rain and contrasting it with their current homes. “When it starts to rain, the house starts flooding and it is worse at night,” one future resident, Candelaria Hernández, said of the one-room shack where she currently lives with seven family members. “You have to wake up to put pots around the house so it things don’t get wet.”