Construction specifications define work results. The results are divided among Divisions and Sections according to CSI's MasterFormat, the industry's organizational standard. Complying with MasterFormat allows specification readers to find information quickly, efficiently.
The organization does not attempt to assign work results to specific trades or subcontrators. Those assignments are the general contractor (GC) or construction manager's (CM) responsibility, unless the specifications explicitly make the assignment. Simply combining work results within a single section is not sufficient.
Specialty design consultants tend to write a single specification section to describe all work results under their control. This is evident in Section 114000 - Food Service Equipment where tables, sinks, carts, shelving, fixed equipment, portable equipment, hoods, and even walk-in refrigerators are specified in this single section. Fortunately, perhaps, a single trade contractor is normally responsible for everything included in this section. No so for others.
Consider building envelopes. Curtain wall, windows, entrance doors, glass, air barrier, sheathing, framing and cladding are typically specified in individual sections as separate work results. However when an envelope consultant is engaged to assist the architect, the consultant may write the specification with some or all these work results combined into a single specification section. Often the presumption is that all will be provided by a single trade contractor as for food service.
Unlike food service, multiple trades are required to assemble the building envelope. The GC or CM may choose to divide the work so skilled subcontractors can be engaged for each work result and to improve productivity to the overall project's benefit.
The specifications can dictate a single source responsibility. It does not matter if the work results are included in a single specification section or not. In some cases, it may be more beneficial to rely on specifications for individual work results, referenced from another section that describes the entire assembly. This method allows the overall system performance to be specified once and provides a place to specify the intersections and transitions among the various products and materials.
Within individual specifications, single source responsibility can be stated:
"Perform Work of this Section and Sections [____], [____], and [____] by single entity."
This requirement must be repeated in every affected section to ensure the single point of responsibility is established. The optimum place to specify this requirement is in the Part 1 Quality Requirements article, the same location where manufacturer, fabricator, and installer qualifications are specified. Additionally, qualifications can be specified for the single entity, too, by reliance on Division 01 or by listing qualification details within the individual sections.
"Systems Integrator: Qualified entity regularly engaged as single, responsible source providing Work of this Section and Sections [____], [____], and [____]."
When using a single specification section, the text suggested above needs only minor modification.
"Perform Work of this Section by single entity."
"Systems Integrator: Qualified entity regularly engaged as single, responsible source providing Work of this Section."
If single source responsibility is required to ensure overall coordination and ultimate quality, the specifications must explicitly state the requirement. Otherwise the GC or CM may and will choose how the work is divided, to best suit their own needs.