The walls of a straw house are under construction in a former boat shop at a Rockland industrial park. They aren’t the stacked bales of a hand-plastered homestead; they’re panels of compressed Maine plants industrially sealed in Maine wood. Croft, a young company that expanded here from a former sardine cannery nearby, hopes to shake up the building industry — plus many other aspects of housing, farming, and life in Maine. It’s part of a growing network here and across the country reexamining plant-based building materials. The underlying concepts aren’t new, but much of the movement today is focused on capturing carbon from the atmosphere in response to concerns about human and environmental health tied to modern construction. Construction and materials made up 11 percent of emissions, according to the World Green Building Council. Andrew Frederick, founder of Croft, sees straw as a way to flip those numbers.