Steel stairs are classified as weight-bearing structures. Assembly and welding entails a greater level of responsibility and is more complicated than welding a gate, for instance. Stairs are made to custom order, and the same rules apply – only galvanized stairs for outdoor use, and only properly primed and painted products may be installed indoors. Stairs come in L- and U-shaped varieties. Naturally, custom designs are also available. The steps themselves can be made of various materials, depending on tastes – wood, steel, stone etc. Spiral staircases are considered a more complicated structure as design must be executed very precisely.