The invention provides a structural building element formed from cold-rolled lightweight sheet steel. The building element may be used as a structural upright or as a beam, and is based generally on building elements with a known C-shaped profile. The profile of the building element of the invention is however based on a continuous curve. Each of a pair of front wall portions extends in a wholly or substantially smooth arc from a central slot opening onto the corresponding lateral side. The rear portion is sinusoidal, comprising a pair of convex wall portions each extending in a wholly or substantially smooth arc from a concave arcuate or substantially arcuate rear central wall portion onto a respective one of the lateral sides.