On a recent really hot day, workers were fixing masonry on the roof of Amir Jina’s building. “And the head contractor said, ‘During the hotter parts of the day, I’m just not going to send out people to work,'” he said. Jina, who’s an assistant professor of public policy at the University of Chicago and founding member of the Lab, said the contractor was worried about the health effects on the workers — and the potential for costly errors amid the heat. So the crew took more time to finish the job. “Probably would have taken two days, ended up taking three or four days just because they needed to stop,” he said.