JOHN D. WAGNER: Can 2x6s be Cheaper than 2×4 Framing?
APA Thinks So. And It Can Prove It.
Guess how many U.S. homes are framed with 2x6s? I was surprised to learn that it’s 45%. (I thought it would be higher.) That 45% 2×6 “market share” is after a 15% increase over the last four years. Tom Kositzky, Director of Field Services for the APA-The Engineered Wood Association, explained the increased use of 2x6s. He said builders are moving to 2×6 framing in part to comply with the widely adopted (and constantly changing) International Energy Conservation Code (IECC). The 2015 IECC recently changed the U-factors in exterior walls. U-factor? In walls? Isn’t that a rating used for windows? Don’t we measure wall performance with R-value?
“The R-value in the code measures the thermal resistance of insulation in the wall, but U-factor expresses the performance of the entire opaque wall assembly, including the studs, sheathing, siding, everything,” Kositzky explained. (The U-factor is different than R-value; the lower the U-factor, the more resistant the wall is to heat transfer.) To comply with IECC’s U-factor demands in some climate zones, 2×4 walls would require continuous insulation in addition to the batts between the studs. Depending on your zone, that might mean R-13 batts and R-5 continuous insulation.
Why is the APA dabbling in the 2×6 vs 2×4 debate and IECC requirements?
Well, Kositzky is part of an effort by the APA to show how builders can use plywood and OSB to meet IECC requirements. Working with the International Code Council (ICC), the APA has published a fantastic guide called IECC Compliance Options for Wood-Frame Wall Assemblies, and it’s a companion piece for the tech reps that APA has in the field to help builders figure out the new Code (The Guide is a free download at http://bit.ly/1jwP3OV).
I’ll admit, the Guide’s title sounds wonky. But take a look at this one, because the Guide shows dealers and builders how to use optimized framing techniques to achieve IECC compliance with plywood- or OSB-sheathed 2×6 walls that can be net-cost cheaper than the 2×4 approach. (APA also has a vested interest in turning back structural insulation sheathing alternatives to plywood and OSB, even though they still enjoy an 80% market share today.)