A recent article in BD+C Magazine, “Building Wrap and the Code; What you Need to Know,” cites International Building Code and ASTM codes, and describes the International Code Council-Evaluation Service’s evaluation criteria for building “wrap” (also known as WRBs, a popular method of protecting building enclosures against moisture intrusion). The article also lists key performance characteristics for evaluation:
Water Resistance – A building wrap should be able to pass both “water ponding” tests, which measure a house wrap’s resistance to a pond of 25 mm (1 in.) water over two hours, and a more stringent hydrostatic pressure test where the wrap is subjected to a pressurized column of water for five hours.
Air Resistance – For an individual building material to be classified as an air barrier, its air permeance must be equal to or less than 0.02 L/(s-m2) @ 75 Pa when tested in accordance with ASTM E2178, Standard Test Method for Air Permeance of Building Materials. However, this air permeance test only measures the amount of air migrating through the material itself and not through holes or gaps in the larger assembly.
Durability – The ICC-ES looks at the tear resistance and tensile strength as the best measure of a building wrap’s durability, since it must be able to withstand the handling and application process without compromising its water resistance.
Vapor Permeability – When selecting a building wrap, look for one that hits the “sweet spot” of 10 to 20 perms to achieve the desired balance of moisture protection and drying capacity.
Flammability – Class A fire rating is the industry standard for WRBs. Ensure the WRB you’re using meet these requirements.
Changing building codes and greater adoption of certain cladding materials have caused specifiers to take a closer look at how moisture is managed in the wall assembly. Advances in building wrap products have added a powerful tool to help achieve these goals.