Will a metal roof prevent ice dams?
A metal roof can reduce the leaking that occurs due to ice damming but it will not prevent ice dams from forming. In some cases it may add to the ice dam formation. A metal roof may warm up faster from solar heat gain than an asphalt roof creating more snow melt flowing to the lower edge of the roof where it can freeze.
The leaking is reduced by having fewer points of entry for pooling water to backup into the roof. Asphalt shingles as well as wood, tile and slate, have multiple nail holes and gaps between them. Metal roofs need fewer fasteners and are usually fabricated in large sheets reducing the available areas for leaks.
A properly installed traditional double locked standing seam roof will have fewer points of entry for water backup than a snap lock, or exposed fastener metal roof. A metal shingle roof that is installed with interlocking joints will also have reduced points of entry for water backup.