The Difference Between Moisture Barrier & Vapor Barrier

The building industry jargon can often leave people confused about home and business renovations. Moisture and vapor barriers are among this jargon, but they refer to a treatment that is vital in construction of long-lasting buildings as well as meeting many new Land Environment Economics and Development (LEED) certifications.

Properly applied vapor barriers help a building withstand damage from moisture while increasing energy efficiency.

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

Modern vapor barriers have allowed builders to place hardwood floors in habitually damp places, such as basements.

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.