Cliff Holste, Materials Handling Editor

As there are growing signs that the economic recovery is real, with increasing unit volumes soon a umber of companies will find that the capacity of their current distribution center is not sufficient to meet current or expected needs in terms of throughput, storage capacity, or other operating requirements.

As we’ve reported before, sizing a new DC is as much art as it is science, and is heavily dependent on the forecast of someone at the company about where sales and unit/case volumes are going to go over the next 3-5 years. (See It's Not Easy to Size a DC's Capacity Correctly.)

In addition to questions around size and throughput needs, companies also need to consider their potential requirements for or interest in materials handling automation when building new or leading an existing buildings. The designs of some facilities are simply more well suited than others in terms of support for materials handling systems inside them. Certainly if a greenfield facility is being planned, companies need to think deeply about what automation may be deployed and the resulting physical facility requirements before any final agreement with an architect or builder.

While it is almost always possible to add at least some level of automation to an existing building (you can now even literally “raise the roof” of many DCs, solving the low clear height restriction that used to be a nearly absolute barrier to sortation systems in some buildings), certain building designs may be inherently less friendly to automation, leading to limitations in system design, and/or higher costs for automate.

This topic is especially pertinent right now, as DC floor space is generally available in most markets at very low rates versus pre-recession days – and therefore may look especially cheap versus building a new facility, as those costs have not come down nearly as much.

Below, take a few minutes to consider a number key building design criteria that should be considered to optimize distribution center performance whether you are building or leasing an existing facility, considering automation or not.

• Size: While size is an obvious factor, there are several considerations often overlooked when determining square footage requirements. The first is the opportunity to reduce total building costs by going up to increase cube, rather than out (see “Building Height” below). The second is that while material handling automation such as picking and carton sortation systems can deliver significant productivity gains, it also takes floor space that must be planned for when building or leasing a new facility.

• Building Height: A traditional “spec” building will have a clear height of 24 to 26 feet, tall enough for 4-high pallet storage racking. However, as it is usually less expensive to build up rather than out, and maximizing storage capacity is an almost universal goal, the trend today for companies commissioning their own facility is to build with a clear height of 32 feet or even greater. At this height, 6-high pallet storage can be used, with some companies going even higher to achieve 8-level storage rack configurations. In most municipalities, fire safety codes have being written to permit ESFR (Early Suppression, Fast Response) ceiling mounted sprinkler systems to be installed in buildings of this height in place of in-rack fire sprinkler systems.

• Floor Flatness: Standard warehouse floors will support normal fork truck movement and activity, but are generally used with conventional, wide-aisle storage configurations (12-foot aisle between racking). Standard floors may preclude use of narrow aisle (8-foot aisles) and are definitely not acceptable for very narrow aisle (5-6 foot aisle) technology, which require so-called “very flat” and “super flat” floor construction, respectively. While these floors are more expensive to install and can add weeks to the project schedule, the long-term gains in storage cube, operator productivity due to faster travel speed, and reduced truck maintenance are often worth the one-time initial building cost. To make this decision, an analysis is required to determine total storage requirements and the optimum rack configuration by comparing building cost, the cost of specialized lift truck equipment, pallet storage density, and expected worker productivity.

It is today now possible to have existing floors improved to “super flat” levels, but obviously this is more expensive than building the floor that way to begin with.

(Distribution Article - Continued Below)

• Column Grid Pattern:  The traditional 40-foot by 40-foot building column spacing is rarely optimum for an engineered DC.  Roof support columns should always be located in the flue space in-between racks.  However, with any of the narrow aisle approaches a standard grid will rarely allow the columns to be buried in the rack, resulting in a significant loss of storage positions.  It is also frequently desirable to make the first bay extra deep to eliminate columns that impede fork truck traffic on the dock, by moving the first column row back to 60-70 feet away from the doors.

• Roof Reinforcement:  It is often possible to hang portions of a material handling automation system from the ceiling rather than using floor supports.  This can both provide for greater movement of vehicles and people around and through the system, as well as allow those portions of the system to occupy otherwise “dead space,” such as above a traffic aisle.  However, the ability to hang conveyors and other equipment is generally dependent upon having defined sections of the building roof structure strategically reinforced during construction to take a greater load per square foot.

A “spec” building will almost never have reinforced roofing. An empty building previously occupied by another tenant may, but likely not consistent with your specific needs. More than you would think, even companies building new DCs don’t get this question answered early enough in the process. While roof reinforcement can usually be added later, it will be a lot more expensive to do so than at the time of construction. That should also be considered in the lease versus build decision.

• Dock Doors:  The typical warehouse building has receiving doors on one side of the building, and shipping doors across on the other side.  While this flow-thru design is often the best configuration, it is sometimes better to look at other arrangements.  For example, placing receiving and shipping doors on the same side of the building may allow both functions to share sortation equipment, using one set of diverts to sort received cartons for palletizing and put-away, and another to build outbound customer orders.  Another advantage is that you can provide one common and secure space for both delivery and pickup drivers to congregate.   While there is usually flexibility to add doors even to a spec building, the final arrangement of doors needs to be closely tied to the material handling system layout, especially for fluid loading and unloading applications. 

• Lighting: Lighting should be placed so that it hangs directly above storage and pick aisles, which will rarely be the case if lighting is in place before the storage system has been designed and laid out

Clearly, there are a number of factors that go in to deciding whether to build or lease a DC and the optimal location for a new facility, including roads, taxes, parking, and many other attributes. Compromises often have to be made.

But making sure you have thought through the operational impacts of existing facility designs, and how the facility design now or in the future will help or hinder adding material handling automation in the DC, will usually save money and allow more options for getting the total system that right for you.

What are your thoughts on the key factors in DC building design? Should companies consider these issues better or earlier in the lease or build process? Let us know your thoughts at the Feedback button below.

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