To some, the idea of buildings that can be delivered by trucks conjures up visions of depressing rural trailer parks. But Project Frog’s designs offer a modern variation on the prefabricated building theme, with cheap modular buildings that are also energy efficient.

Project Frog’s buildings are making inroads in education and child care. Because they are well lit and comfortable, but snap together into well-defined floorplans, they work well for classrooms and play areas.

The company’s building units also offer variable energy options. Those who need the bare minimum will get a building that is simply low-energy, but extra options like ground-source heat pumps and solar paneling can push the buildings to be energy neutral, or even net producers.

This $8 million round comes in a bit short of the $8.6 million the company was hoping for when it raised the first $4 million tranche from RockPort Capital Partners. Other investors weren’t disclosed. Project Frog is based in San Francisco, Calif.