Air Barriers vs Vapor Barriers

Despite their importance, there is often confusion about their functions, applications, and the differences...
Air Barriers vs Vapor Barriers

In the construction industry, ensuring the durability, energy efficiency, and comfort of buildings is paramount. Two critical components that play a significant role in achieving these goals are air barriers and vapor barriers.

Air Barriers vs Vapor Barriers

Despite their importance, there is often confusion about their functions, applications, and the differences between them. This article aims to clarify these concepts, helping professionals and students alike understand when and why each barrier is used.

Understanding Air Barriers

Definition and Purpose: An air barrier system is designed to control the unintended flow of air into and out of a building enclosure. The primary goal is to minimize energy loss and prevent moisture from entering the building envelope through air leakage, which can lead to condensation and mold growth.

Materials and Placement: Air barriers can be made from a variety of materials, including sheet goods (such as house wraps and building papers), foam boards, and fluid-applied membranes. They are installed throughout the building envelope, including walls, roofs, and foundations, to create a continuous barrier that stops air leakage.

Benefits: The implementation of an effective air barrier system enhances building durability, improves thermal comfort for occupants, and reduces energy costs by minimizing the heating and cooling load.

Understanding Vapor Barriers

Definition and Purpose: Vapor barriers, also known as vapor retarders, are materials used to prevent moisture from diffusing through the walls, ceilings, and floors by vapor diffusion. They are crucial for controlling moisture levels within building assemblies, thus protecting against dampness, mold, and structural decay.

Materials and Placement: Vapor barriers are typically made from plastic sheets, foil-faced paper, or specially treated drywall. The correct placement of a vapor barrier is dependent on the climate; in colder climates, it is usually installed on the interior side of the insulation, whereas in hot, humid climates, it may be placed on the exterior side.

Benefits: By controlling moisture diffusion, vapor barriers help in maintaining the structural integrity of the building, prolonging the life of construction materials, and ensuring a healthy indoor environment.

Air Barriers vs. Vapor Barriers: Key Differences

  • Function: Air barriers control air leakage, while vapor barriers limit moisture diffusion.
  • Material Permeability: Air barriers must be impermeable to air but can vary in their permeability to vapor. Vapor barriers are specifically designed to be impermeable to water vapor.
  • Location and Application: The application of air barriers is extensive and continuous throughout the building envelope. Vapor barriers have more specific placement, typically near the warm side of the thermal insulation, varying with the building’s geographical location.

Choosing the Right Barrier

The decision to use an air barrier, a vapor barrier, or both depends on various factors, including the building’s design, location, climate, and the specific requirements of the construction project. Professionals must assess these factors carefully to determine the most appropriate solutions for moisture and air control in their buildings.


Air barriers and vapor barriers serve distinct but complementary roles in the construction of energy-efficient, durable, and comfortable buildings. Understanding the differences between them is crucial for construction professionals and students. By applying this knowledge effectively, they can ensure the long-term performance of buildings and contribute to a more sustainable built environment.

FAQ Section

  • Q: Can a material serve as both an air barrier and a vapor barrier?
  • A: Yes, some materials can function as both an air and vapor barrier, provided they meet the required permeability and continuity criteria for both applications.
  • Q: How do climate and building location influence the choice between air and vapor barriers?
  • A: Climate affects moisture and air movement, influencing the type and placement of barriers. For instance, vapor barriers are often installed on the interior side in cold climates to prevent moisture migration into the building envelope, while air barriers are universally necessary to control air leakage regardless of climate.

By understanding and distinguishing between air and vapor barriers, construction professionals can make informed decisions that enhance building performance and longevity.