According to the US model building codes, any material with an air permeability of less than  0.02 L/(s • m²) @ 75 Pa [ 0.004 cfm/ft.² @ 1.57 lb./ft.²]* when measured per ASTM E283 or E2178** is considered an air-impermeable air barrier material. Both of these tests apply a pressure difference across the foam of 75 Pa [1.57 psi] and measures the air flow in liters/sec [cfm] through one square meter [square foot] the material.

For spray foam insulation, thickness matters when it comes to air permeability.  Most closed-cell SPF insulations are air-impermeable at about 1” thick; most open-cell SPF insulations are air-impermeable at 3.5” to 5.5” thick. The thickness where the foam becomes air-impermeable is usually found in the product data sheet or code compliance report.

It should be noted that simply installing an air barrier material may not be enough. While choosing SPF insulation is an excellent first step, building assemblies and the entire enclosure must also meet air permeability standards.  For more information on air barrier materials, assemblies, accessories and systems, visit the Air Barrier Association of America’s (ABAA) website at www.airbarriers.org. 

*this is the same air permeance as a sheet of ½” thick gypsum board

**The ABAA only recognizes ASTM E2178 for measuring a material’s air permeance.

NOTE: The next Foam Fact Friday will be on December 4.

We wish you a safe and Happy Thanksgiving!

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