what building materials are environmentally friendly?
['Recycled Steel. Utilises steel already in existence for structural use in a home. ... ', 'Bamboo. Bamboo is increasing in popularity as a building material. ... ', "Sheep's Wool. ... ", 'Straw Bales. ... ', 'Precast Concrete. ... ', 'Earth. ... ', 'Plant-Based Polyurethane Rigid Foam.']