Metallic roof material and roofing method using same

A metallic roof material comprising:

• a front substrate made of a metal sheet, the front substrate comprising a body portion formed into a box shape;
• a back substrate arranged on a back side of the front substrate so as to cover an opening of the body portion;
• and a core material made of a foam resin is filled between the body portion and the back substrate, the metallic roof material being tightened to a roof base by driving at least one tightening member into the body portion,
• wherein a top plate portion of the body portion comprises at least one protruding rib comprised of at least one protrusion formed in a part of the metal sheet and disposed along a side of a polygon or along a circle, and wherein the metallic roof material is configured such that the tightening member is driven into an inner region of the protruding rib, and
• wherein the at least one protruding rib further comprises at least one opening portion that communicates an outer region with the inner region of the protruding rib.