Vapour barrier usage is designed to prevent moisture from passing through during which condition?

• A. It Prevents Moisture From Passing Through Only In Cold Work
• B. It Prevents Moisture From Passing Through Only In Hot Work
• C. It Allows Moisture To Pass Through
• D. It Blocks Heat

Answer: (A)

Vapor barriers are meant to stop water vapor from moving from warm, humid spaces into colder areas where it would condense. In cold conditions, moisture in inside air tends to diffuse toward the cooler surfaces of walls or insulation and can condense there, causing damage. A vapor barrier on the warm side blocks that diffusion, keeping the insulation dry and preventing condensation problems.

So the best choice highlights preventing moisture passage during cold work, which is when condensation issues are most likely to occur. It’s not about blocking heat, and it isn’t intended to allow moisture through or to be used only in hot conditions.