Alejandro Herrera was commuting two hours each way into Mexico City for architecture school when he turned a vacant rooftop into a tiny home in the city center.

In the heart of the very desirable Roma Norte district, his new home measured just 42 square meters (450 square feet), but it opened to a garden terrace of the same size.

The initial home was built with a steel frame and plywood and glass panels (to keep costs down). Seven years later, the exterior had deteriorated with the weather and Herrera decided to create Mexico’s first Passivhaus (the very demanding energy efficiency standard from Germany) to cut energy costs. With a tight insulating envelope, the current home uses two-thirds less energy.