Specifications

Drawings show what is to be built and where; specifications describe the quality of materials and workmanship and how it will be checked. Together with the bill of quantities and conditions of contract, they define the contract. A vague specification leads to disputes and poor work; a clear one lets every bidder price the same thing and lets the engineer accept or reject work objectively.

Specifications may be general, applying to standard items across many works, such as a public works department's standard specifications, or particular, written for a specific project's special requirements. They may be prescriptive, stating materials, proportions and methods, or performance-based, stating required properties and test results while leaving the method to the contractor. Most combine both: concrete may be specified by grade, maximum water-cement ratio and minimum cement content (performance plus limits), while curing is prescribed.

A good specification clause covers materials (standards they must meet), workmanship (method, tolerances, sequence), testing and acceptance (tests, frequency, criteria, and what happens on failure), and measurement and payment. It refers to standards by number and edition rather than repeating their text, avoids conflict with drawings and other clauses, and uses clear language: 'shall' for requirements. An order of precedence in the contract decides which document governs if they conflict.

Where a specification and a drawing disagree, site staff should not choose the easier option; they should raise a query and record the engineer's decision.