Air Barrier Materials, What are air barrier materials

Air barrier materials speaks to what are air barrier materials, why air barrier materials and types of air barrier materials.

These are which act to reduce air leakage through a building assembly. Examples of these specific materials include building wrap, gypsum wallboard, polyethylene sheet plastic, rigid foam insulation, liquid applied membranes or various formulations such as caulking, sealants, gaskets, tapes and much more.

To function as an air barrier must be resistant to the passage of air, it must have sufficient strength and rigidity to withstand the air pressure differentials that act upon it. Especially where it spans movement joints, it must be sufficiently resilient to accommodate movement without failure and as well, it must be durable enough to perform its function throughout the life of the building.

The greater a material’s resistance to the passage of air, the lower its air permeance and the better its performance as an air barrier. Air permeance is measured according to ASTME E2178 and is expressed as cubic feet of air per minute per square foot of area at 1.57 lbs per square foot, which is .3 inches of water which exerts an air pressure or as in metric units, as litres per second per square meter of area at 75 Pascals of air pressure.

An air performance of one cfm per square foot or 1.57 psf is equal to approximately 5 L/s-sq m at 75 Pa. The most commonly cited standard for air barrier materials is an air performance not greater than 0.004 cfm per sq ft at 1.57 psf or 0.02 L/s at 75 Pa.

An air barrier product must be able to resist air pressure, acting either inward or outward across the building assembly, without damage or excessive deflection. Flexible sheet materials such as building wraps, plastic sheets, roofing membranes and flexible flashings are especially vulnerable. If not properly supported or adequately fastened, these materials can tear, stretch or pull loose and become ineffective as air barriers.

Damage caused by air pressures can also lead to the failure of materials to perform other important functions such as keeping liquid water out of tne building or resisting the diffusion of water vapour. If an air barrier material remains intact but deflects excessively under alternating cycles of positive and negative air pressure, it can pump air in and out of a building assembly, reducing the effectiveness of insulation and increasing the risk of water vapour transport into the assembly.

These barrier materials must be able to accommodate the normal thermal and structural movements that occur within building systems without undue wear or failure.

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