Differential movement occurs when independent structural components are adjoined at different parts of the building. These conditions can occur in roof systems at flashings, penetrations, adjoining roof areas and mechanical penthouses.
Prefabricated roof curbs have been in use since the roof has been utilized for something other than keeping weather out. And in this one sentence lie the benefits and the detriments we face in the roof curb business everyday. The primary function of the curb is to keep weather out while supporting/flashing the equipment on it.
The perimeter edge is one of the most vulnerable points of a low-slope roof system. This area is continually susceptible to wind-uplift damage and moisture infiltration.
The roofing industry is now at a point where we should collectively define a uniform standard for the determination of moisture content in roof systems. It is time to move past the days of the "educated toe," i.e., subjective claims of how the system felt as it was walked across. A standard would benefit all sectors of the industry preventing frivolous lawsuits and unsubstantiated claims driven by the pursuit of profit.