According to the U.S Department of Energy, as much as 30% of a home’s energy stems from air leakage? The great news is that common wood structural panels can be a central part of a proactive plan to cut down on air leaks: 3/8 Performance Category or thicker plywood and OSB panels are code-recognized air barrier materials that can contribute to tighter, more energy-efficient homes.
What the Codes Say
North American wood structural panels, including plywood and OSB 3/8 Performance Category or thicker material, are recognized as air barrier materials by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the International Residential Code (IRC), the International Energy Conservation Code (IECC) and the Canadian Building Code.
According to air permeance data from an ASHRAE-sponsored research project completed in 2002 by National Research Council (NRC) Canada, measurements for six tested wood structural panel products were below the threshold of 0.02 L/(s.m2) at 75 Pa for an air barrier material. Specifically, it found the following:
In a related project, NRC measured the air permeance values for North American plywood and OSB and found both to be “very air-tight materials.” Specifically, the six plywood products with thicknesses from 3/8 inch to 1/2 inch had air permeance between 0.00013 and 0.010 L/(s.m2) at 75 Pa, and the six OSB products with thicknesses from 3/8 inch to 15/32 inch had air permeance between 0.00066 and 0.014 L/(s.m2) at 75 Pa.
The 2021 IECC requires whole house air infiltration to be rated no greater than 3 ACH at 50 Pa in Climate Zones 3 to 8 and no greater than 5 ACH at 50 Pa in Climate Zones 0, 1, and 2. Energy Star® v3, 3.1 and 3.2 recognize wood structural panels as rigid air barriers; Energy Star currently permits building leakage rates of 3 to 4 ACH at 50 Pa, depending on the climate zone.
Approach Walls as a System
While wood structural panels meet the requirements for air barrier materials, they are not fully air impermeable—air will move through the WSPs under pressure just as it will through gypsum board or another other recognized air barrier material. This reinforces that airflow control is not about a single material but an assemblage of materials that make up an air barrier system.
Wood structural panels are excellent air barrier materials that are rigid and durable, two key characteristics to consider when choosing a material to be part of a continuous air barrier system. When using these materials, designers or builders must choose an appropriate method for sealing openings and panel joints. Contact the joint sealant or tape manufacturer for information on how their product works with wood structural panel substrates.
In addition, do not confuse an air barrier with a water-resistive barrier, which is required over wood structural panel wall sheathing. While properly sealed wood structural panels can serve as a standalone wall air barrier assembly, many builders combine the water-resistive barrier with continuous wood structural panel wall sheathing to serve as a combined air barrier and water-resistive barrier system.
Find more information on using wood structural panels as air barriers as well as guidance on key wall joints and penetrations to target in APA’s free-to-download Technical Topic: Air Permeability of Wood Structural Panels as Air Barriers and Simple Air Sealing with OSB and Plywood Sheathing publications or in APA’s free, on-demand webinar—CEU’s available.