The weight of metal is a common misconception that a metal-roof-contractor will quickly clarify for you. Metal is actually significantly lighter than asphalt shingles, clay tiles, or slate roofing materials. Because it is so lightweight, a metal-roof-contractor can sometimes install it directly over one layer of old shingles. This "recover" method saves money on labor and disposal fee... https://kkroofspecialist.com.sg/metal-roof-contractor/