Knowledge is Power

Rack System Design: The Importance of Flue Space

As we’ve discussed before in this blog, there’s a surprising amount of math and measuring involved in something so seemingly simple as pallet rack design.

This time around, we’ll be talking about the flue space–the space between rows of pallet rack or between a row and a wall.

Read on to find out why it’s important and how to include it in your designs for the best results.

Why Leave Room?

Warehouse space is valuable so it seems like nonsense to leave all that room between rows of rack. So why do it?

pallet overhangFirst, remember that rack is designed so that the beams support most of the weight of the loads, even if you’re using pallet supports or decking. As a result, some of the load must extend past the front and back of the rack system. 42″ deep rack is popular because the most common pallet depth is 48″, allowing for 3″ of overhang both front and back, as shown in the picture to the right.

As a result we already need 6″ of room between back-to-back rows of rack, but there are several good reasons that the design standard for back-to-back rows doubles that number:


  • First and most obvious, to avoid causing pallet and load damage by crashing them into the load in the other row’s bay.
  • To make the Fire Marshall happy and avoid fines. There must be room between the rows for the water from sprinklers to reach the floor.
  • To have a place to hide building columns. No one wants a column in a bay and eliminating pallet positions

flue space

Also be aware that leaving room for rows of rack that are next to a wall is important as well. This prevents load damage and damage to pipes, conduits and other building facilities that may be mounted on the wall. This is especially important in cooler applications where the walls consist of thin metal and styrofoam and are very easily damaged. In fact, we strongly recommend pallet stops for those applications.


More on Row Spacing

ROW SPACERAs long as we’re on the subject, here’s some information about when row spacers and wall ties are needed.


  • Row spacers and wall ties add strength and stability to back-to-back rack systems.
  • Only necessary when the frame height exceeds 6 times the depth. In other words, row spacers and/or wall ties are needed for a 42″ deep frame that exceeds 21 feet in height.
  • When they are used, they should be installed with one for every 10 feet of height.

Note that while that’s an Interlake row spacer shown, we also stock Ridg-U-Rak for your use and because we’ve gotten requests, we’ve started stocking 12″ Mecalux row spacers for you as well.

If you want to learn more about rack system design, remember that we’ve placed a lot of information on our How-To page.  If it doesn’t have what you need or you want more information just get in touch. We’re here to help you succeed.

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