What is a closed specification?

A closed specification is characterized by specifying a particular trade name or brand for materials and explicitly disallowing any substitutions. This means that the specifications dictate that only the indicated product may be used, ensuring consistency in material quality and performance. By limiting the choices to a specific brand, the designer or architect can maintain a particular aesthetic or technical standard that they believe is necessary for the project. This approach can simplify the construction and procurement process, as it eliminates variation and potential discrepancies that could arise from using different materials that claim to meet the same standard.

The other options differ in key aspects. Allowing substitutions, listing approved brands with the possibility of new entries, or providing general descriptions involves a degree of flexibility that contrasts with the rigidity of closed specifications. Such approaches might be suitable in scenarios where alternatives are acceptable, or where the market dynamics allow for variations in brand or quality without compromising the overall project intent.