Which joint or seam must be sealed as directed by standard duct sealing requirements?

• A. Traverse joints Class C
• B. Butt joints Class A
• C. Seam joints Class B
• D. Corner joints Class D

Answer: (A)

Understanding how duct joints are sealed helps here. Standard duct sealing assigns a sealant class to each joint type to control leakage to a specific level. Traverse joints—where duct runs cross or intersect as the path changes direction—are a common leakage point, so they’re specified to be sealed with Class C sealant. This level provides reliable sealing and accommodates minor movement and thermal changes without being overly heavy or impractical.

So, the correct pairing is sealing traverse joints with Class C. Other joint types are matched to different classes, which is why the traverse joint with Class C is the appropriate choice.