Air Barrier Vs Moisture Barrier

When this air moves from location to location due to an air pressure difference the vapor moves with it.

Air barrier vs moisture barrier.

High performance air and water barriers resist air and water intrusion which reduces the amount of moisture vapor in the panels. Germain director of osb ewp quality and technical at lp building solutions. Vapor barrier is the more common terminology though organizations like the u s. Weather resistive barrier systems lead the fight against moisture penetration said brian st.

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. This requires an air barrier system or air pressure control that may or may not be combined with an air barrier system. An air barrier must also resist air pressure differences that act on them. In addition tyvek weather barriers help keep bulk water out to help protect insulation in walls of both residential and commercial buildings.

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. Department of energy say that the term vapor diffusion retarders more accurately represents the goal of a vapor barrier. In the strictest sense air barriers are also vapor barriers when they control the transport of moisture. 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.

This is a type of migration of water vapor. 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. Fire resist products are formulated for burn resistance and have passed the nfpa 285 test in many wall assemblies. 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. Essentially air barriers minimize or restrict heat loss and gains through conduction. Even at wind speeds of 5 mph a wall without an air barrier retains less than 40 of its original installed r values. Moisture barriers and vapor barriers are both building materials designed to prevent water from getting past the barrier.