Narrow Aisles and High-Density Storage: The Warehouse Gold Standard

By Jim Hess, Contributor

From the name alone, it’s obvious that high-density warehousing requires the efficient use of space. Industry research backs up this assumption, as average warehouse capacity used was identified as the single most popular benchmarking metric in the 2020 Warehousing Education and Research Council DC Measures Report (https://werc.org/news/508610/WERCs-2020-Annual-DC-Measures-Operational-Benchmarking-Report.htm). Best-in-class operations use an average of 90% of available warehouse capacity and 100% during peaks.

But maximizing space is not about capacity alone – operations must be able to move inventory quickly. Insufficient storage can cause goods to pile up in aisles, producing congestion that hampers throughput, requires additional product touches and creates greater risk of product, facility and equipment damage. And with consumer expectations for ever-faster delivery, that type of congestion becomes increasingly incompatible with aggressive throughput targets.

Demand Is On The Rise

Warehouses are squeezed at both sides – as they race to enable the swift flow of goods and rapid throughput, ecommerce growth and demand for variety press them to stock larger inventories, pushing storage capacity to the limit.

The simple answer to both challenges is more space. But as warehouse leaders can attest, securing additional space is challenging and expensive. Average rent growth for warehouse and logistics facilities has exceeded 5% for five straight years (https://www.joc.com/international-logistics/industrial-real-estate/aro-2020-us-warehouse-lease-rates-rise-again-2020-despite-softer-market_20191230.html). In 2019, rents kept rising and vacancy rates stayed near historic lows, despite record growth in new warehousing space. And while the unprecedented construction might hint at relief, space is not a temporary concern – Zebra reported that nearly 60% of warehouse leaders named capacity utilization as one of their top expected challenges over the next several years.

High-Density Storage Configurations

Aisles that are narrower than standard can enable warehouses to get the capacity boost they need. When measuring the choice of a costly new facility or expansion against finding more capacity in existing space, re-racking a facility or portions of a facility with narrower aisles can provide the necessary boost in capacity without the expense of construction.

While a standard aisle is 12ft wide, operations can implement a narrower spec to fit additional storage aisles in the same footprint – provided the right type of lift truck is there to service it. Reach trucks are capable of handling 8-10ft aisle widths, depending on height and weight, and very narrow aisle (VNA) turret trucks can work in aisle widths as narrow as 6ft. Multiply the impact across several aisles and the capacity gains really start to stack up. For example, based on space saved on aisle widths alone, an operation with 4ft loads could save 40ft over ten aisles by reducing standard aisles to aisles 8ft wide and using reach trucks. In that saved space, they could set up two additional aisles, or four runs of rack, and still have additional freed space available for use.

Warehouses pinched for capacity can also bolster their storage with higher racks. This allows operations to take advantage of unused cubic volume by building up, rather than out – a natural extension of the push to store more in the same space with narrower aisles. Paired with the right slotting strategy and equipment, leveraging higher-level storage offers an efficient solution to compound capacity gains.

But as previously noted, increasing capacity is only part of the story – moving inventory efficiently is critical to success for high-intensity warehouses. While reach trucks can reach heights as high as 37ft, allowing them to service much higher-level storage locations compared to counterbalance trucks, it’s important to evaluate your equipment options for fast cycle times. When your operators are lifting and lowering to and from greater heights, even seconds shaved off each cycle add up – even one additional pallet move per hour equates to 7% greater productivity. Higher lift and lower speeds along with better acceleration and braking capabilities help drive that increase.

Another way to pack even more capacity into narrow aisles is with double-deep storage, in which the pallet at the front of the location has one stored directly behind it. Reach trucks with the necessary reach capabilities can extend into the racking to reach pallets in the deeper position, allowing warehouses to achieve up to 50% more capacity than single selective racking. The right solution may be a mix of double-deep racking for some products for maximum storage density and single selective racking where case picking is required for improved productivity when access to the SKU is paramount.

Do Not Overlook The Operator

In any narrow aisle environment, prioritizing the operator is fundamental to success. Equipment with characteristics to support operator comfort, speed and precision can help prevent productivity from suffering due to challenges of working in higher, narrow aisle configurations, like maneuvering in tight spaces, placing and retrieving loads at greater heights and double depths, discomfort, fatigue or greater time waiting for loads to be lifted and lowered.

For narrow aisles to be an efficient solution for capacity and productivity targets alike, operators need sufficient maneuverability to work in smaller spaces, performance to move quickly and visibility to precisely position forks at height. Equipment features such as cameras, built-in LED lights and fork laser levels that show fork positioning when placing or retrieving loads at height can help boost operator accuracy and confidence. But ergonomics play an important role, too, helping fend off fatigue so that operators stay fresh and productive all shift long. The total package of narrow aisle storage is equipment and operators coming together to deliver the higher efficiency and capacity today’s high-intensity warehouses need to excel. WMHS

Jim Hess is the Director of Warehouse Business Development, Yale Materials Handling Corporation. He brings over 35 years of warehouse and lift truck experience with special expertise in 3PL, grocery, retail, food and beverage to his role overseeing warehouse business development and related products at Yale (www.yale.com).