A small, 600-square-foot guest house planned for the historic Knapp’s Castle property would be built with hemp-based material if approved by planners. Hemp Technologies, a North Carolina-based company, said it is working with the property owners to build the small cabin with the eco-friendly material, which they say is more resistant to fire and also avoids molding, rotting, and other similar wear and tear. The “hempcrete” actually petrifies over time, according to Hemp Technologies.