Weighing the Options for Selective Pallet Rack Depth

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Pros & Cons of Using 42” vs. 48” Deep Uprights with Standard 48”x 40” Pallets

Industry experts agree that selective racking is the most common type of pallet racking.  It’s relatively simple in form and versatile enough to be used across a variety of storage applications.  The main components of selective pallet rack are columns and struts fixed together to create the upright and shelf beams that connect the uprights to form the pallet rack bay.

Upright height is largely based on the amount of available warehouse space (ceiling height) and inventory volume (# of levels/bays).  But one design feature that deserves some extra thought is the upright frame depth – did you know there were options for accommodating standard 48” x 40” pallets? In case you didn’t, we’ll help walk you through the variables….

Rack frame depth can be 42” or 48” deep for storage applications using standard-sized pallets.  Both depths have pluses and maybe challenges depending on how you look at it.

Note: If you’re using odd-sized pallets, the Apex team can help you design a custom pallet rack configuration to accommodate the pallet dimensions. 

Here are some selective pallet rack frame guidelines…

The common formula to determine upright depth for standard pallets is to subtract 6” from the pallet depth.  Example: Using a standard 48” long x 40” wide GMA-style pallet:

Subtract (48” – 6″) = 42″ deep uprights

Pallet Racking Apex Warehouse SystemsAs you can see on the image to the right, the 42” depth will allow 3” of pallet overhang in the front and back of the rack. Both front and rear pallet overhang must be accounted for in terms of determining aisle depth (front overhang) and proper adherence to fire safety requirements (rear overhang).

Note, however, that a minimum of 6” of open space is required behind the rack row. This open space is called a flue space, and it is a standard fire safety regulation. Therefore, if you are designing a system with two selective rack rows in a back-to-back configuration, the minimum flue space would be 12” or 2 x 6”.  With the shallower 42” deep rack, the challenge for fork truck operators is to make sure the pallet overhang does not exceed the expected allotment and crowd the flue space.

Height-to-Depth Considerations

Pallet rack frames that are 42″ deep and taller than 20’ will exceed the recommended 6:1 height-to-depth ratio and may require additional engineering, i.e. special anchors, base plates, or overhead pallet rack ties. The Apex design team and provide specific project recommendations.

Design Considerations of the 42” Upright Depth:
  • Reduce steel needed
  • Reduce overall cost
  • Harder to manage open flue space
  • May require additional engineering for heights exceeding 20’
  • Easier for the forklift to place the pallet securely on the front and rear beams

The other option would be to design the upright to the full pallet depth of 48”.  Obviously, this would require more steel and, therefore, increase the cost of the system, but there are several advantages that might outweigh the additional cost.

Selective pallet rack design Apex Warehouse SystemsDesign Considerations of the 48” Upright Depth:
  • Easier to maintain flue space
  • No pallet overhang, neater aisles
  • When used with wire decking, safer for picking at the ground level
  • More steel, more upfront cost
  • Easier for the forklift to flush the pallet to the front beam to ensure secure loading

Using a 48” deep upright with a 48” deep pallet allows little to no room for error in terms of forklift loading.  The beams are spaced precisely to support both the front and rear of the pallet, so the responsibility is on the forklift operator to accurately place the pallet.  Pallet supports and/or wire mesh deck can be added as an extra measure of safety to help support the pallet boards and help temporarily hold the pallet should the operator not initially catch both front and rear beams squarely. The pallet would have to be replaced so the load is on both the front and rear beams.

Neither pallet supports, nor standard deck is meant to hold the full weight of the pallet.

Choosing between the two upright depths will not affect the system layout.  The 6” difference is made up in the flue space between the two racks in a back-to-back scenario by reducing the spacing from 12” to 6”, or not at all in a single-deep system as the aisle would be designed to accommodate the pallet depth either way.

We hope this blog answered a few questions regarding selective pallet rack depth design considerations.  If you’d like additional information or system design support, our experienced pallet rack engineers are here to help – give us a call today, and we’ll get right on it!