If you need a ladder for a particular task, you might want to know more about ladders in general. This may help in your choosing the right ladder for the job. The rigid ladder is usually the ladder type used for most tasks. There are many types of rigid ladders, from the fixed type to the roof ladder type. The fixed ladder is the most basic, and has no moving parts. Extension ladders are the type that can be lengthened, since one part is nested in the other for storage. The ones that form a reverse V are called step ladders. The one with a platform is of course called the platform step ladder. Roof ladders have hooks that set them firmly hooked on the roof. Aluminium is the choice material for many ladders, except those for electrical work.