Whenever one considers storage options for their warehouse, it is very common to gravitate to merely looking at what options yield the most pallet positions. Density, after all, is the goal. Stick as much product as possible into a given space.
One common mistake that is made is to let density drive your design process. Density is the ultimate goal, but focusing on operational efficiency is more critical. Putting a system in that does match your operation may yield more pallet positions on paper, but in reality, can actually produce significantly less than anticipated.
“Pigeon Holing” as it is called can occur when the design does not match the operation. This is where product cannot be stored in the manner in which it was designed. This creates holes in the storage density and does not allow you to take advantage of all the positions you have created.
A common comparison is one that centers around two high density approaches, Pushback rack and Drive-In rack.
Pushback rack is where each pallet resides on a series of trays within each pallet location. Every subsequent pallet that is placed in a particular location has the ability to “push” the previous pallet back one location. This allows multiple pallets of the same SKU to be housed in a very dense fashion. Pushback is an ideal LIFO (Last In First Out) storage layout. It also allows for more pick facings giving you the ability to store a larger number of SKU’s in a given aisle. The ideal application is one where you have multiple pallets of the same SKU that need to be stored and retrieved in a medium paced operation that does not require a FIFO (First In First Out) methodology, e.g. non-perishable items that do not have a short life-span.
Comparatively, Drive-In rack creates lanes down an aisle that allow a lift truck to travel into the lane to store product. This is the densest storage media available. However it has its limitations. Only one SKU can be placed in a lane. Once the lane is loaded, pallets must be pulled from the front backwards. Once a pallet is removed, deeper pallet will not be available if you load the empty position back up. So, to gain access to the back pallets, you have to leave the front positions open. This reduces your ability to take advantage of the density you have created. The ideal application for Drive-In rack is where you load a lane and flush that lane in its entirety. Fast moving operations can benefit from this design.
The bottom line is: Don’t be driven by maximizing pallet positions at the cost of the efficiency of your operation.