Here is a brief walkthough on ladders. The rigid ladder is usually the ladder type used for most tasks. Rigid ladders have many kinds – fixed, extension, step, platform step, and roof. The most basic of ladder types is the fixed ladder; it has no moving parts. Extension ladders are the type that can be lengthened, since one part is nested in the other for storage. Step ladders are joined by a hinge at the top of its inverted V form. The one with a platform is naturally called the platform step ladder. Roof ladders come with hooks that set them firmly hooked on the roof. Aluminium is the choice material for various ladders, except those for electrical work.