In many cases, a common plan of development or sale consists of many small construction projects. For example, an original common plan of development for a residential subdivision might layout the streets, house lots, and areas for parks, schools and commercial development that the developer plans to build or sell to others for development. All these areas would remain part of the common plan of development or sale until the intended construction occurs. If your smaller project is part of a larger common plan of development or sale that collectively will disturb one or more acres (e.g., you are building on 6 half-acre residential lots in a 10-acre development or are putting in a fast food restaurant on a 3/4 acre pad that is part of a 20 acre retail center) then you need permit coverage. The "common plan" of development or sale is broadly defined as any announcement or piece of documentation (including a sign, public notice or hearing, sales pitch, advertisement, drawing, permit application, zoning request, computer design, etc.) or physical demarcation (including boundary signs, lot stakes, surveyor markings, etc.) indicating construction activities may occur on a specific plot. You will be required to still meet the definition of operator in order to be required to get permit coverage, regardless of the acreage you personally disturb. As a subcontractor, it is unlikely you would need a permit.
However, where only a small portion of the original common plan of development remains undeveloped and there has been a period of time where there is no ongoing construction activities (i.e., all areas are either undisturbed or have been finally stabilized), you can re-evaluate your individual project based on the acreage remaining from the original common plan. If less than five but more than one acre remains to build out the original common plan, then a permit might still be required, but you can treat your project as part of a "small" construction activity and might be eligible for the waivers available for small construction activities (e.g., one of six lots totaling 2 acres in a 50 acre subdivision can be treated as part of a 2 acre rather than 50-acre common plan). If less than one acre remains of the original common plan, your individual project could be treated as part of a less than one acre development and no permit would be required.