Answer Capacity Questions Before Building a Mezzanine
Your warehouse is at capacity thanks to the double-digit growth you’ve had over the past five years. Options are limited. If building is too expensive and renting space is impossible in today’s tight real estate market, expanding upward with a mezzanine could be the way to go.
But you need to approach the purchase of a mezzanine with eyes wide open. You can’t go down to the local mezzanine store and pick one the same way you buy a car.
Before going any further, it is critical you know and understand how you intend to use the mezzanine. What is the planned use for the mezzanine? There is a huge difference between using a mezzanine for more office space and light storage than using it for heavy manufacturing or storing three-ton parts.
There are significant questions you must address. The most important of these questions is capacity.
Capacity is about weight, but that is not all. It’s how that weight is distributed across a platform. The capacity requirements for a mezzanine vary based upon how the mezzanine is used. However, there are general capacity guidelines for a mezzanine, measured in pounds per square feet (psf). These guidelines come from the International Building Code and are:
- 60 psf (elevated platforms/offices)
- 125 psf (storage warehouse – light/light manufacturing)
- 250 psf (storage warehouse – heavy/heavy manufacturing)
Building from the bottom up
What do these numbers mean? The basic answer is the approximate amount of weight distributed across the mezzanine platform. But much more information is needed prior to setting up a mezzanine. Let’s start at the bottom and work our way up.
The basis for any structurally sound building or mezzanine starts with its foundation. In this case, it’s your floor slab. A typical floor slab in a warehouse is six to eight inches thick. This thickness provides approximately 25,000 lbs capacity—enough support for a mezzanine in most situations. However, the slab capacity depends upon the soil beneath it. Sandy soil or soil in areas with a high water table exists may require additional support.
Achieving the additional support may mean adding concrete footings. Adding concrete footings can be expensive and create delays. A construction crew must cut through the slab, removing the questionable soil and replacing it with poured concrete. Columns from the mezzanine then rest on these new footings, providing the appropriate support.
You should always consult a building architect or engineer and confirm the slab is capable of supporting the increased load. An engineer will determine the concrete footing needed. That person will also have the final say and guarantee the mezzanine is rated for the required capacity. Remember, a less expensive alternative to concrete footings is designing the mezzanine columns closer together. This reduces column load while providing the necessary support.
Mezzanine – how big?
Assuming the capacity of the floor slab and the amount of additional support (if needed) permits, you are ready for the next step. This is the size of the mezzanine. What are the planned dimensions? There is a secondary question to consider also. How many columns will support the structure?
For the sake of example, let’s use a 20’ x 20’ mezzanine for a total of 100 sq feet. We locate nine load-bearing columns at 10’ intervals including one in the center of the mezzanine. The mezzanine has a uniform load of 12,500 lbs across the entire mezzanine. In other words, each column can support 12,500 lbs. If you need more space below the mezzanine, you may need to adjust the number of columns. But remember, the longer the span of columns the lower the uniform load.
Finally, your mezzanine can support a specified capacity across the entire deck area. However, you need to consider the amount of weight in any given area on the mezzanine. A heavy load resting in one location is referred to as a point load. This point load may include heavy machinery, a pallet of product awaiting shipment or similar stationary weights sitting in one location over an extended period. This creates issues. It may be minor such as damage to the mezzanine deck or more serious such as a failure of that section of the mezzanine.
Investing in a mezzanine adds space and longevity to successful warehouse operations. The key is understanding the capacity requirements.