Cantilever Racking: Arm Capacities, Sizing and What It Stores Best

Cantilever racking stores long, heavy, non-palletized material — lumber, pipe, tube, bar stock, sheet goods, moulding, furniture — on horizontal arms bolted to free-standing columns. Because there is no front column in the way, a forklift can set a 24-foot bundle across four arms in a single motion and pull it back out the same way.

That open front is the entire point. Selective pallet rack has an upright every 8 to 12 feet, and anything longer than the bay either overhangs into the aisle or gets cut. Cantilever removes the obstruction and lets the load length set the run length. If you are still deciding between systems, our overview of the types of pallet racks for warehouse storage covers where selective, drive-in and push-back each earn their floor space.

The trade is density. Cantilever gives up cubic efficiency compared with a well-designed pallet run, so it belongs where the material genuinely cannot be palletized — not as a default.

Quote requests fail most often on base depth. A buyer picks 48-inch arms to hold a 4-foot-deep load, gets a 48-inch base, and then discovers the run needs floor anchors it was not planning to install because the overturning moment is right at the edge of what the base can resist unanchored.

Read a capacity table carefully. Published arm ratings such as “1,500 lb per arm” are stated at a specific arm length, and the same arm profile at 60 inches will be rated well below its 36-inch figure. The reason is bending moment: the load’s distance from the column multiplies the force the arm-to-column connection has to carry, so an off-centre load can overload an end arm even when the bay total looks safe.

Then apply the three-capacity rule. Arm capacity times the number of arms gives you a theoretical column load, but the upright has its own rating and the whole bay has a third. Whichever is lowest is your real number. Cantilever systems are designed to ANSI MH16.3 — the Rack Manufacturers Institute specification written specifically for cantilevered racks, separate from MH16.1 which covers pallet rack. If a supplier cannot tell you which specification their arms are designed and tested to, that is the answer to your next question. Where the SKUs are cases rather than long stock, the sizing exercise moves to lane depth and pitch instead of arm capacity, and carton flow rack pick rates are what the layout gets judged on.

Spacing follows the load, not the catalogue. Twenty-foot structural tube is stiff enough to span arms at 6-foot centres. The same 20 feet of vinyl trim or thin-wall conduit will sag between them and take a permanent set, so it wants arms at 3 to 4 feet. A useful field check: load one bay, sight down the material, and if you can see daylight bowing between arms, add an upright rather than de-rate the load.

The decision is usually made by traffic, not by load. A run that sits in a low-traffic bay of a climate-controlled building can be roll-formed at a real saving. A run in the main aisle of a steel yard, where a forklift will eventually clip a column, should be structural — the same logic we walked through for structural versus roll-formed pallet racks, and it holds here with more force because a cantilever column carries an eccentric load and has less redundancy to give.

Single-sided runs go against a wall. Double-sided runs stand in open floor and share one column line between two faces, which roughly halves the steel cost per arm and is almost always the better buy when you have the floor for it.

What decides the layout is the truck, not the rack. A counterbalance lift needs enough aisle to square up to a 20-foot load and back out with it — that is a different number from the right-angle stack aisle on its spec sheet, because the load is now longer than the truck. Work the geometry before you order steel; our breakdown of forklift dimensions and aisle width gives the working figures by lift class.

One practical rule for long stock: plan the aisle at the load length plus the truck’s turning radius plus a safety margin, then walk it with tape on the floor before the racking arrives. Retrofitting an aisle after a double-sided run is anchored is an expensive lesson.

California treats storage racks as structures, and the trigger is the height of the topmost load position. The thresholds are consistent across jurisdictions because they come out of the California Building Code and ASCE 7 — the City of Fresno’s storage rack submittal requirements set them out in the form most Central Valley plan checkers use.

Two details catch buyers out. The first is that the measurement is to the topmost load position, not to the top of the column — so leaving a spare arm level up high costs you a permit tier whether you load it or not. The second is that anchoring is what converts a low rack from exempt to permitted, which is a genuinely counterintuitive rule the first time you meet it. We covered the plan-check process end to end in our guide to warehouse racking permits in California, including what a plan set actually has to show.

None of this is a reason to build short. It is a reason to decide the height before you decide the budget, because the paperwork tier is not a line item you can value-engineer out later.