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Racks: Terminology

When searching for the perfect rack, it can be helpful to know some of the basic terminology on this subject.

Base unit

A rack base unit is always required at the start of a rack row. It comprises 2 frames and shelves. Unlike add-on units, a base unit can also be used individually.

Add-on unit

An add-on unit can only be attached to a base unit or an existing rack. Each rack row first requires a base unit, which can then be expanded with any number of add-on units. An add-on unit comprises 1 frame and shelves / storage trays. Unlike base units, an add-on unit cannot be used individually.


In the case of a double-row rack, two rack rows are positioned back to back so form a single static unit.


A double-sided rack is one that can be accessed from both sides. In this case, the shelves rest on longitudinal bars, thus removing the need for diagonal bracing. The shelf can then be used from either side.


Racks are braced either with diagonal supports (cross braces) or by means of longitudinal bars/beams. Diagonal bracing is frequently employed for shelf racks. In the case of pallet racks, the necessary support is provided by the bars/beams within the frame.

Compartment height

Describes the distance from the upper edge of the warehouse floor or shelf to the upper edge of the next shelf. This spacing is also referred to as the buckling length.

Shelf load

The shelf load describes the maximum weight of the specific "compartment", i.e. the individual shelf. The shelf load indicates the total weight that a shelf can accommodate, provided that the load is evenly distributed.

Unit load

The unit load describes the maximum weight that the complete rack can support – not including the weight of the rack itself. The sum of the individual shelf loads must not exceed the permitted unit load. The unit load is influenced by the shelf height.

Impact protection

When racks are loaded and unloaded using forklift trucks (e.g. pallet racks), they must be equipped with impact/collision protection at the corner areas and passageways. The impact protection must be at least 300 mm high and able to absorb impact energy of 400 Nm.

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