CSI identifies several types of specifications, including:

Descriptive specifications – describe materials and methods in detail.

Performance specifications – describe required results and performance criteria.

Proprietary specifications – designate specific products or manufacturers.

Reference standard specifications – define requirements by citing recognized industry standards rather than repeating all technical details.

A reference standard specification works by referring to standards issued by organizations such as:

Trade associations (e.g., industry associations),

Standards organizations (e.g., ASTM, ANSI, ISO),

Other recognized bodies that publish consensus technical standards.

The specification then simply states that materials, products, or work must comply with the named standard. This reduces repetition and promotes consistency and clarity.

Therefore, a proper basis for a reference standard specification is a trade association standard, which is Option C.

Why the other options are incorrect:

A. Project manual for similar projectPrevious project manuals may be informal references for the specifier, but they are not recognized standards. A reference standard specification must refer to a published technical standard, not another project’s contract documents.

B. Design intentDesign intent is expressed more directly in performance or descriptive specifications, not in reference standard form. Reference standards rely on external, recognized standards, not internal design intent statements alone.

D. Manufacturer's specification sectionReferring to a specific manufacturer’s literature or section is characteristic of a proprietary specification, not a reference standard specification. Reference standards must be based on independent, consensus-based standards, not one manufacturer’s materials.

Key CSI Reference Titles (no links):

CSI Construction Specifications Practice Guide – Types of specifications, including reference standard specifications and their proper use.

CSI Project Delivery Practice Guide – Relationship of specifications to industry standards.

CDT Body of Knowledge – “Specification Types and Methods of Specifying.”