Types of pallet racking, and what actually separates them

Four families, not eight equal options

Most lists of rack types are flat, which makes eight names look like eight comparable choices. They are not. FloorCast3D groups them the way the geometry actually behaves, because the family decides what the drawing, the bill of materials and the simulation each have to do differently.

Two things commonly listed as rack types are not rack types

Back-to-back is an arrangement of selective racking, not a system: two single-deep rows mirrored against each other, sharing a flue between them. It changes the row spacing and the flue rule, not the way a pallet is stored or retrieved. FloorCast3D carries it as a flag on a selective zone for exactly that reason.

VNA — very-narrow-aisle — is a property of the truck, not the steel. The rack is ordinary selective racking; what makes the aisle narrow is a turret or combi truck that does not need room to turn. Put it on the rack type and you end up unable to describe the common case, which is ordinary racking worked by a narrow-aisle fleet. The forklift aisle width guide covers what each truck class actually needs.

This matters beyond vocabulary. Model back-to-back or VNA as a type and you cannot represent a back-to-back double-deep zone, or a narrow-aisle drive-in lane, without inventing more types. Both are legacy values in FloorCast3D’s own file format — old projects that stored them are migrated to selective on load, with the arrangement and the truck recorded where they belong.

The eight systems side by side

“Usable” below is the planning fraction of raw positions an operator can realistically keep full once honeycombing and lane access are accounted for — the same figures FloorCast3D applies when it states effective capacity next to installed capacity.

Single-deep

The baseline. Every pallet is reachable, so nothing is lost to blocked positions.

Double-deep

Two pallets deep off one aisle, worked with a reach truck. The front pallet has to move before the back one can.

Drive-In

The truck drives into the lane on rails carried by the frames. Closed at the rear, so one SKU per lane and the deepest honeycombing of the eight.

Drive-Through

A drive-in lane open at both ends: enter one aisle, exit the other, so the lane rotates.

Push-Back

Nested carts on inclined rails. Worked entirely from the front face and usually shallow, which is why it honeycombs far less than drive-in.

Pallet Flow

Gravity rollers with brake control. Charged at the high rear face and picked at the low front, so it rotates itself.

Cantilever

Arms, not beams. For long or awkward loads that a pallet position does not describe.

Carton Flow

Case-level gravity flow at the pick face, typically with reserve pallets on the levels above it.

The distinction that decides most projects: how many faces

Density gets the attention, but rotation is what usually settles the choice. A lane worked from a single face is LIFO — the last pallet in is the first one out. Drive-in is LIFO because its rear is closed; push-back is LIFO because its nested carts are loaded and picked at the front. A lane charged at one end and retrieved at the opposite end is FIFO and rotates itself: pallet flow loads the high rear and picks the low front, and drive-through simply opens both ends of a drive-in lane.

If your product is dated, lot-tracked, or turns slowly enough that age matters, that single property eliminates half the density options before floor utilization is even discussed. It also changes the building: a FIFO lane needs an operating aisle at both ends, so the densest-looking system on paper can cost you a whole aisle’s worth of floor once it is laid out against a real footprint.

What the steel does differently

The families do not just store differently, they are built differently, and it shows up directly in the bill of materials. Drive-in and drive-through carry the pallet on rails hung off the frames, and because the lowest load sits on the slab, a lane has one fewer rail level than it has pallet levels. Push-back and pallet flow carry their load on inclined rails or flow track that bear on a beam at every frame line down the depth — every level sits on structure, so there is no free floor position at all.

That difference decides how cost scales with depth, which is the part most easily got wrong by hand. Selective racking sets a beam pair per pallet depth, so going double-deep genuinely doubles the beams. Deep-lane systems rest their pallets on continuous rails, so making a lane deeper adds rail and frames but does not multiply the beam count. Estimating a drive-in lane as though it were stacked selective bays overstates the steel substantially.

Cantilever is the clean break: arms off a column, no load beams at all. A drawing that renders beams on a cantilever run is describing a bill of materials that bills zero of them — which is why FloorCast3D draws arms, braces and bases as their own members rather than reusing the selective bay.

Carton flow is a level, not a rack

Carton flow belongs on this list because everyone shops for it by name, but it is structurally a different kind of thing: a sloped roller or skatewheel bed carrying cases, mounted on one beam level inside an otherwise normal bay. The common real-world configuration is a single upright frame with case-pick flow beds at the bottom and reserve pallets on the levels above — one rack, two jobs.

Modelling it per level rather than per rack has a consequence worth knowing before you plan around it: deep-lane density systems have no per-level beam to mount a bed on, so carton flow cannot be combined with drive-in, push-back or pallet flow. A standalone gravity-flow rack is simply the case where every level in the bay is a flow bed.

Choosing, in the order the answers actually come

Start with rotation: if the product is dated or lot-tracked, you are choosing between selective and the FIFO systems, and the LIFO options are already out. Then take SKU count against pallets per SKU — deep-lane density only pays when one SKU fills a lane, because a half-filled lane is a blocked lane, which is what the usable fractions in the table above are describing. Then the building: FIFO lanes need aisles at both ends, and lane depth has to divide sensibly into the column grid you actually have.

Only then does the mix get drawn, and it usually is a mix. Reach for density on the fast movers, selective for the long tail, cantilever for anything that was never on a pallet. To size the building before choosing any of it, the warehouse capacity calculator answers how many pallets fit; the rack layout guide covers rows, flues and back-to-back spacing, and the beam spacing guide covers the elevation.

Frequently asked