Clear height
Clear height — The usable vertical space after lights, sprinklers, beams and ducts are subtracted from the roof. It is the one storage dimension you cannot widen later without a building project, which is why it gets first call on the layout.
Aisle width
Aisle width — The working width a specific truck needs to enter an aisle, turn and leave with the load it actually carries. It is a property of the truck and the load, not of the racks — the racks just inherit whatever the truck demands.
| Truck type and turn radius | sets aisle width, and that sets how much floor is aisles |
|---|---|
| Stock rotation speed | sets how many picks per hour the aisles must serve |
| SKU count versus units per SKU | sets storage style — selective, drive-in, shelving |
| Floor flatness and bearing | limits how high it is safe and legal to build |
| Sprinkler and beam clearances | caps the top level; check the local fire code with the authority |
The aisle is chosen by the truck, not the rack
Every layout argument starts from the wrong end when it starts from the racks. The sequence that works: pick the truck for the loads you actually move, read its aisle requirement from the manufacturer’s figure for your actual pallet dimension and load weight, then let that number decide how much of your floor becomes circulation. On the same footprint, the difference between a counterbalance truck’s aisle and a reach truck’s aisle is several rows of pallet storage — which is why “we will sort the truck out later” quietly spends the building. And read the requirement as an operating figure, not a swerve-to-the-bollards figure: an aisle that only works when the operator aims perfectly is an aisle that stops working on the rainy Monday.
Height is storage you already paid for, so it is the pickiest
Above the sprinkler line the building is mostly unused air, and every extra level is the cheapest steel storage you will buy. The catch is that everything else in the plan must also reach the top: floor flatness and bearing capacity, a truck that can place accurately at the top level with the load you actually weigh, lighting that lets the picker read labels up there, and sprinkler coverage designed for the geometry that results. Meet those and the top levels are the best storage you own. Skip them and the top levels fill with the stock nobody wants to fetch, which is a slow way of demolishing your own layout with your own hands.
Before the drawing: floor, sprinklers and the authority
Three checks belong before any rack quote, because each can redraw the plan after it has been signed. The floor: survey flatness and bearing where the frames will stand, because rack loads concentrate a whole stack’s weight on small footprints, and an older slab was never promised anything about pallet racks. The sprinklers: rack geometry and sprinkler design interact, and filling aisles or adding in-rack heads is a fire-protection change with a review attached. The authority: clearances and seismic requirements are set locally, not by any catalogue, and the racking supplier and the fire-code officer should see the same drawing before construction, not after.
Does a narrower aisle always mean more storage?
Only on the drawing. A narrower aisle does convert floor into storage, but the truck has to live with it every shift: reach trucks that shrink aisles need flatter floors and better-maintained guidance, and their travel and pick speeds drop in tight quarters. The honest comparison is storage volume per pallet moved per hour, not storage volume per square metre, and the answer can run either way depending on what you move.
Is going up really cheaper than spreading out?
Per stored pallet, usually yes, because the building and the floor slab are already paid for and the extra cost is steel, a taller truck and safety equipment. But height is pickier than floor: it demands better floor quality, more careful load discipline, lighting that reaches the top levels and sprinkler design that matches the rack. Buying height without buying those four things just converts your storage problem into an uptime problem.