The Difference Between Moisture Barrier & Vapor Barrier

Moisture and Vapor Barriers

• These two terms essentially refer to the same thing. Moisture barriers and vapor barriers are both building materials designed to prevent water from getting past the barrier. Vapor barrier is the more common terminology, though organizations like the U.S. Department of Energy say that the term "vapor diffusion retarders" more accurately represents the goal of a vapor barrier. No vapor barrier is capable of stopping all moisture from passing through.

Air Barriers

• One term that does have an arguably distinct but similar meaning is air barrier. According to research by BuildingScience.Com researcher Joseph Lstiburek, air barriers are needed all the time while vapor barriers are not always a good idea. Air barriers, like insulation, control the movement of moisture-laden air -- not fully stopping the presence of moisture but allowing its dispersal. These layers are made of many different materials and provide a self-contained pocket of air to control the movement of thermal energy into and out of a building. Air barriers are often used in conjunction with vapor barriers to increase energy efficiency and the overall life of the building.

Types of Vapor Barriers

• Vapor barriers are found in wide range of materials and applications. Rigid foam insulation acts as a relatively effective vapor barrier. Polyethylene plastic is commonly used and has among the least amount of measured moisture permeability. Specifically-design vapor barrier paints and primers are often applied to bricks and provide a versatile vapor barrier. Aluminum foil blocks the most moisture, but this is not always a useful feature.

Common Vapor and Air Barrier Applications

• Construction workers recommend vapor barriers for different reasons in different circumstances. Vapor barriers are applied to the interior walls in climates which are predominantly cold while they are best applied to exterior wells in predominantly hot climates. Finished basements often receive a vapor barrier layer between the concrete and the floor treatment to prevent damage from heavy rains or other moisture seepage.