Most warehouse managers are familiar with storage rack beams, uprights, and decking. However, an often overlooked but essential component for rack safety and performance are row spacers. These rack members enhance the stability and structural integrity of the system, as well as increase overall operational safety.
What Are Row Spacers?
Row spacers — also called back-to-back ties — are steel components that connect two or more parallel rows of selective pallet rack arranged back-to-back. Installed between the uprights of adjacent rows of rack, the spacers lock the columns together typically by way of bolted connections.
Their presence maintains longitudinal flue spacing — typically 6-, 8-, 12-, or more inches — depending on pallet overhang and fire protection requirements. Rack engineers also specify row spacers to connect double- or triple-deep rack configurations.
In all of these rack designs, the connections enable an operation to increase their storage density and capacity, noted Chris Aprile, Senior Structural Engineer at Steel King Industries. The company is a member of the Rack Manufacturers Institute (RMI).
“By tying two rows of uprights together, row spacers enable back-to-back rack placement. This reduces the number of aisles and maximizes storage area per square foot,” he explained. “Without spacers, row placement needs to be farther apart for safety and stability, which reduces storage density.”
Improved Lateral Stability and Structural Stiffness
Tying two or more rows of selective pallet racks together with spacers also helps create a more rigid and stable structure in the cross-aisle direction. This improves the lateral stability of the rack system, particularly in tall or seismic configurations.
“Row spacers do not directly increase the load-carrying capacity of individual frames. However, they do contribute to the system’s overall stiffness. They may also provide a degree of redundancy in resisting cross-aisle lateral forces — especially when used with braced upright frames,” said Aprile.
Further, row spacers improve the structural performance of pallet rack systems in the cross-aisle direction. Their presence enhances lateral stiffness and helps limit deformation during a seismic event.
“While they are not primary seismic bracing components, row spacers provide valuable system-level stability. They also reduce the risk of sway or tipping. That makes them especially important in tall or heavy-duty storage applications,” he added.
“Additionally, row spacers help restrain back-to-back uprights from leaning toward or away from each other under lateral movement, such as forklift impact or seismic motion,” Aprile continued. “This added stiffness helps maintain vertical alignment and improves system integrity. In operations with tight forklift aisles or frequent pallet handling, row spacers are especially important to reduce swaying and misalignment.”
How Many Row Spacers Are Necessary?
A rack engineer specifies the number and placement of the row spacers from the top to the bottom of the uprights, noted Aprile. Taller uprights require more than shorter ones.
“A typical design specifies rack spacers to be a minimum of 8 feet apart vertically,” he said. “However, if that placement interferes with other connections — such as beam connections to upright column posts — it’s acceptable to make small adjustments to the spacing. Moreover, bolting a row spacer too close to the beam connection may restrict beam clip installation or limit access for hardware tightening.”
Additional design and engineering specifications are in RMI’s ANSI MH16.1 Standard for Design, Testing, and Utilization of Industrial Steel Storage Racks, he added.
Row Spacers Maintain Flue Space
Another important safety aspect of utilizing row spacers is to maintain adequate flue space around stored product for fire suppression. Most new warehouses incorporate overhead ceiling mounted sprinkler systems that depend on unobstructed heat flow to activate. To work properly in the event of a fire, the heat must be able to rise to the ceiling. Obstructions prevent that, delaying the sprinklers’ automatic operation. Likewise, blocked flue spaces inhibit the flow of water.
“The National Fire Protection Association publishes the NFPA 13 standard for the installation of sprinkler systems,” Aprile noted. “It recommends a minimum of 6 inches of longitudinal flue space between back-to-back racks in most standard warehouse configurations. Row spacers help maintain this critical spacing. The ventilation space promotes effective heat rise and water penetration, improving sprinkler system performance during a fire.”
Rack Inspections Should Include Row Spacers
When performing routine storage rack inspections, it is important to check the spacers along with all other racking components. Key assessment points include checking for damage, looseness, proper engagement, and bolts or clips that are tight and secure.
“Specifically, inspect for any signs of damage that may compromise the spacer’s structural function. This includes dents, bending, cracks, or corrosion,” advised Aprile. “Also ensure rack spacer installation is at correct vertical intervals — typically coordinated with beam elevations or per manufacturer instructions. Missing or deformed row spacers can reduce rack stability, increase sway in the cross-aisle direction, and compromise flue space, especially under dynamic or seismic loads.”
Learn More About Storage Rack Safety
Looking for more ways to improve storage rack safety in your facility? Visit RMI’s Frequently Asked Questions (FAQs) page. This resource covers topics such as fire codes, inspections, maintenance, proper loading, addressing damage, and more.
