What does it mean?
Preliminaries describe project-wide obligations and costs that support carrying out the works rather than forming a single permanent work item. Examples can include site management, welfare, temporary facilities and security. Some costs occur once and others depend on duration. Clear allocation helps prevent omitting site overheads or charging the same cost in both a trade rate and the preliminaries.
In practice
A site facility costing 500 per week for 20 weeks contributes 10,000. An extension of duration may change time-related costs even if the quantities of permanent work remain unchanged.
Keep in mind
For a project record, note the document reference, revision and agreed measurement or contractual basis beside the quantity. Keep assumed information visibly separate from confirmed information. If two parties use different definitions or inclusions, resolve that difference before comparing amounts. These explanations are general estimating context; the wording of the applicable contract and its administration process must be checked for the particular job.