A prescriptive specification conveys the requirements of a project through a detailed explanation of the materials that the contractor must use and the means of installing those materials. This type of specification will typically be formatted in a manner similar to the following sections:
- General: This typically contain references to national standards (commonly based on the NBS software), design requirements, a list of required submittals from the contractor to the architect/engineer, quality control requirements and product handling requirements.
- Products: This will describe in detail the various products required for the task covered by the specification along with the individual structural and performance requirements of each product.
- Execution: This will explain how to prepare the materials and conduct the installation, including the testing requirements to be followed.
Prescriptive specifications shift more of the project design control onto the shoulders of the designer and away from the contractor by establishing a set of rules that is to be followed for each project component. This type of specification provides more certainty regarding the final product composition than the performance specification, and is very frequently used for highly complex portions of a project.
A prescriptive specification is very common in traditional contracts, whereas a performance specification is expected to be prepared for a Design & Build contract where the contractor requires more flexibility in the final selection of products and workmanship.