Air Barrier Vs Moisture Barrier

Department of energy say that the term vapor diffusion retarders more accurately represents the goal of a vapor barrier.

Air barrier vs moisture barrier.

This is a type of migration of water vapor. In the strictest sense air barriers are also vapor barriers when they control the transport of moisture. High performance air and water barriers resist air and water intrusion which reduces the amount of moisture vapor in the panels. A proper air barrier is one of the most important elements of a successful building enclosure and one of the most overlooked.

The key to moisture control is the control of air transported moisture. Stopping air transporting moisture to the interior of a wall assembly is critical because when the warm vapor touches the cool interior walls the vapor turns to liquid by condensation. This requires an air barrier system or air pressure control that may or may not be combined with an air barrier system. The confusion arises because air often holds a great deal of moisture in the vapor form.

There is a big difference between air transported moisture and vapor diffusion. In some cases the reduction in mechanical equipment size and cost can also offset the cost of the air barrier system in addition to lowering utility bills. An air barrier must also resist air pressure differences that act on them. Vapor barrier is the more common terminology though organizations like the u s.

Fire resist products are formulated for burn resistance and have passed the nfpa 285 test in many wall assemblies. To increase moisture barrier protection ccw also provides a variety of flashing products for use with air and vapor barrier systems. When this air moves from location to location due to an air pressure difference the vapor moves with it. Moisture barriers and vapor barriers are both building materials designed to prevent water from getting past the barrier.

Even at wind speeds of 5 mph a wall without an air barrier retains less than 40 of its original installed r values. Buildings which have a properly installed air barrier system can operate properly with a smaller hvac system as the mechanical engineer does not have to compensate for a leaky building. Given the amount of heat loss due to air transmission and the potential moisture damage from air leaks air barriers should be getting a lot more attention than they are. Essentially air barriers minimize or restrict heat loss and gains through conduction.