Distribution centres are employed for a combination of dispatch, inspection, picking, receiving, sorting and storage activities. The extent of picking and sorting functions required to make up outgoing loads is a major determinant of the layout and configuration of purpose-built distribution centres and the extent and cost of the materials handling system. While schemes can be particularly tailored to the requirements of the clients, there are but a limited number of generic layouts that are used. The main sources of variation between schemes include the number and type of loading bays, the size and arrangement of high-bay storage and the orientation of the structural frame to suit racking. The main distribution types are as follows:
Bulk Storage and Simple Sorting
Low bay units, with single dock faces, are targeted at the third party logistics market. Sorting usually takes place in the receipt and dispatch area, and thus, only sorting of large units of measure or pallets can be undertaken. Units of up to 25,000 metres2 in size are developed speculatively to meet this demand, based on a standard institutional specification.
Automated Retrieval and Storage
These distribution centres have high bay bulk storage areas, up to 20 metres high, and with automated stock-handling equipment, in concert with a low bay picking and sorting area adjacent to a single dock face. The design can be tailored to accommodate the specific requirements of the racking and materials handling equipment. Units with a combination of high and low bay space are typically developed as a pre-let but will need to conform to institutional standards to allow for long-term flexibility to provide security to funders.
Throughflow distribution centres are distinguished by having dock faces on opposite ends of the building, enabling receipt and dispatch functions to be separated. Typically this requirement is driven by complex sorting activities occurring at both sides of the bulk store. Sophisticated materials handling systems associated with throughflow warehouses allow the unit size of goods being picked to be reduced, improving stock control and reducing in-store inventory. Distribution centres designed to a throughflow principle range in size from 25,000 to 75,000 metres2 or more. These distribution centres are usually developed as pre-lets or as joint developments between logistics companies and their end-user clients.
Cross-dock layouts are highly specialized and are typically only used to provide distribution hubs for parcel delivery companies etc, where speed of transit rather than storage is the main driver. Provision for bulk storage is not usually provided and the scope of materials handling equipment is limited to that needed to facilitate the transfer of goods between vehicles. The main driver behind the size of a cross-deck scheme is the number of loading docks required.
Regardless of the design of the distribution center, flexibility and longevity are also important considerations for investors, with envelope performance and building services capacity being key areas that can differentiate buildings by reducing the likelihood of premature obsolescence. Some developers are beginning to pay greater attention to sustainability and environmental impact issues – specifying, for example, porous paving materials to minimize the impact of large areas of hardstanding on drainage run-off.
Owing to their efficiency and dedication of design before use, distribution centers are built and staffed to handle all sorts of inventory management and handling needs. Their design will continue to improve as ways of processing stock will change in the future.