Logistics News: Rack up Savings by Putting the Squeeze on DC Storage Space

For most DC applications, the factors that determine the optimum storage scheme are both numerous and interwoven. The types of products handled, throughput requirements, building design, and staffing levels will all influence the choice of storage systems, as will the budget and expected ROI.

Single deep racks: The most widely used type of pallet rack.  There biggest advantage is accessibility - they offer 100% access to every pallet load, therefore providing maximum pallet slot utilization.  However, there disadvantage is they decrease storage density because only one pallet load (SKU) is available on each picking face.

Double deep racks:  Consists of two back-to-back racks that are two pallets deep, substantially increasing storage density by cutting the number of lift truck aisles required in half when compared to single deep rack.  However, the potential for some honeycombing is increased along with reduced load selectivity if different SKUs are placed in the same slot.

Drive-in/drive-through racks:  Offer a way to eliminate nonproductive aisle space.  If your operation involves many pallet loads that contain the same SKU, drive-in/drive-through racks could be a perfect high density solution.  However, because they produce a first-in/last-out product flow, they often aren’t the right choice for applications that require stock rotation.

Pallet flow racks:  Feature first-in-first-out (FIFO) stock handling, high storage density, and low maintenance.  Although they can be get to be a little pricy when compared to the above static racks, they are never the less ideal for applications that have a relativity small number of SKUs along with a high pallet throughput requirement.

Mobile rack systems:  Can be considered when there is sever space restrictions and low to medium throughput requirements.  A mobile rack installation requires a single aisle and fits into cramped quarters.

Unit Load Storage & Retrieval Systems:  Deployed in a highly automated, high-rise facilities with AS/RS operations, this approach can provide extremely high storage density, coupled with nearly flawless inventory control.

Obtaining the Best Storage Cube Utilization

One of the most basic planning decisions relative to pallet rack layout is the width of the lift truck aisles.  Do you want to use a conventional; a narrow-aisle (NA); or a very-narrow-aisle (VNA); rack configuration?  The following is a brief overview of what each approach has to offer.

Conventional: Conventional pallet rack layouts typically use aisle widths of 12 feet, and are usually no more than 4 pallets high permitting the use of standard counterbalanced fork lift trucks.  To translate this into storage positions, 1,000 pallets will require about 10,500 sq. ft. of floor space.

Narrow Aisle (NA): By choosing to go with a narrow-aisle (NA) layout, you will be able to store the same 1,000 pallets in about 6,000 sq. ft. of floor space, which equates to a savings of about 40%.  This is because the NA layout utilizes a specially designed compact Reach Truck that can stack pallets 6 high while operating in an 8 ft. wide aisle.  The Reach Truck is equipped with a pantograph type of reach mechanism that scissors the pallet forward from the mast.  In operation, the truck turns a right angle to face the rack, and then extends the pallet load out into its proper slot.  Due to the truck’s compact overall length and the fact that it carries its forks in a retracted position, it requires substantially less room to turn than does a conventional counterbalanced fork lift truck.

A variation of this truck design is the double-reach, which uses a double pantograph mechanism to increase the length of its reach.  A double-reach truck can store pallets two-deep, permitting you to use double-deep rows of rack.  Double-reach trucks require an additional 6” of aisle width for their turns (8’-6” total).  With this layout you’ll only need 4,500 sq. ft. to accommodate 1,000 pallets.

Very Narrow Aisle (VNA): If you need to squeeze even more storage capacity out of your warehouse you should consider a very-narrow-aisle (VNA) rack layout.  With VNA storage you can narrow the aisle widths down to 5’-6” or even less, while increasing rack heights to as many as 9 slots (40 feet.) 

Now you’ll need just 3,200 sq. ft. of floor space to store 1,000 pallets.  However, VNA requires a highly specialized rack-guided or wire-guided Swing-Reach Turret Truck.  However, the price reflects their sophisticated designs and performance capabilities.

In addition, your aisle floor must be “super flat”.  There are concrete floor specialists that work with contractors to pour a super flat floor for new construction and/or provide corrective concrete floor laser grinding in existing buildings. 

The type of pallet storage rack, the rack layout, and the type of lift truck should all be selected based on the storage and throughput requirements of your operation and the uniqueness of your building.

Agree or disgree with our expert's perspective? What would you add? Let us know your thoughts for publication in the SCDigest newsletter Feedback section, and on the website. Upon request, comments will be posted with the respondent's name or company withheld.