Vapor stops are commonly installed at expansion joints, valve joints, and insulation joints. Which location is NOT a typical place to install vapor stops?

• A. Expansion joints
• B. Insulation joints
• C. Valve joints
• D. Control box interruption points

Answer: (D)

The main idea is that vapor stops are used to preserve the vapor barrier where the insulation is interrupted or where movement could create a path for vapor to bypass the insulation. They are placed at expansion joints to accommodate movement without tearing the seal, at valve joints where valve components can introduce a gap in the barrier, and at insulation joints to bridge the gap between insulated sections. A control box interruption point, however, is not part of the piping insulation boundary and does not create a vapor path that needs sealing, so it isn’t a typical place for a vapor stop.