Which statement best describes the role of an air barrier in a building envelope?

• A. An air barrier minimizes air leakage and is achieved with tapes, sealants, flashing, and penetrations sealing in a continuous system.
• B. An air barrier is only for moisture control.
• C. An air barrier increases air leakage.
• D. An air barrier is only required in basements.

Answer: (A)

Air barriers are about stopping unwanted air movement through the building envelope. Their main job is to minimize air leakage, which helps keep the indoor temperature more stable, reduces energy use, and also limits the amount of moisture carried by air that can condense inside wall or attic assemblies.

For an air barrier to work, it has to be continuous across the whole envelope—walls, roof, and foundation—so there aren’t gaps where air can sneak through. That continuity is achieved by detailing and assembling components carefully: using membranes or materials that form a continuous layer, sealing joints with tapes or sealants, flashing at edges and connections, and meticulously sealing around penetrations like pipes, wires, and duct openings.

It’s important to note that this barrier is not just about moisture control, and it does not increase leakage. It reduces leakage and helps protect insulation performance and indoor air quality. And it’s not limited to basements; a proper air barrier is a feature of the entire building envelope.