Do Not Build Warehouses with Sky-High Racks

“Why did we install high racks?” I ask. The answer is ready: “To use the warehouse volume better.” But which measure tells us that?

The limits of a volume calculation

In the example considered, the warehouse volume up to the usable ceiling was approximately 10,000 m³, the total volume of rack spaces was 3,000 m³ and the total volume of material boxes was 1,500 m³.

1,500 / 10,000 = 15%. Under these definitions, this is the ratio of box volume to building volume. Box volume should not be confused with the solid volume of the material or pallet-location occupancy.

The remaining 85% is not all waste. Safe aisles, fire and access requirements, equipment manoeuvring space and structural clearances also occupy this volume. These cannot be reduced arbitrarily during improvement.

The time needed to reach a box

In the same example, retrieving a box from a high rack with dynamic locations takes approximately 180 seconds, including finding the address, walking, positioning the vehicle, lifting, scanning and confirming. Taking a box from a fixed location at hand level might take about 5 seconds.

These two figures do not measure the same scope. In the second case, supermarket replenishment, picking, transport and recording happen in another cycle. Without including that work, we cannot count the entire 175-second difference as net savings.

Designing storage and replenishment together

Under suitable conditions, high racks can hold reserve or slow-moving inventory. For small boxes frequently consumed in production, a nearby material supermarket may be considered. The solution depends on product size, consumption, replenishment frequency and safety conditions.

Using PFEP—Plan for Every Part—we can define packaging quantity, point of use, location and supply method. Kanban can organise the replenishment signal, while a regular material-supply route can organise transport.

Let us assess the warehouse using space and volume utilisation, total handling effort, inventory accuracy, safety and timely supply to production together.