"Advanced framing" has been around a long time. Introduced as "optimum value engineering," or OVE, by the Department of Housing and Urban Development (HUD) in the 1960s, the concept is simple: use less wood in the wall so you can use more insulation. For decades, the idea has hung around without really catching on. But in recent years, as government policy has driven a rapid toughening of the energy code, advanced framing has started to emerge as an important strategy for meeting code without pricing your product out of the market.
The purest and simplest form of the advanced framing concept is to switch from walls framed with 2x4s at 16 inches on center to walls framed with 2x6s at 24 inches on center. The two versions use roughly the same amount of wood and have roughly the same bearing capacity, but the 2x6 wall has about 30% less thermal bridging. The 2x6 wall's greater stiffness against lateral wind loads on the face of the wall is a freebie, and the reduction in construction labor — fewer pieces to handle, fewer nails to drive — offers a net savings. Other wood-reduction tricks, such as two-stud corners, cut thermal bridging further.
And advanced framing extends beyond studs. Framers can move headers into the rim joist area, for example, or even omit the headers in cases where the rim joist alone is sufficient to carry the loads from above. Raised-heel trusses, which allow deeper insulation at the intersections between walls and roofs, also fall into the category of advanced framing.
But those changes are more complicated, and they raise engineering questions. Can a header integrated into the band joist really carry the required load? Will raised heel trusses topple if a wind load pushes the roof sideways? As the codes get tougher on energy waste, engineers are taking a closer look at the structural issues involved in meeting the energy code — and as data accumulates, framing solutions that work are finding their way out of the engineering lab and into the International Residential Code.
Engineer Vladimir Kochkin, of Home Innovation Research Labs (formerly known as NAHB Research), has been studying integrated rim joist headers and raised heel trusses, along with colleagues at the lab. A january 2013 report, "High-R Walls for New Construction Structural Performance: Integrated Rim Header Testing," lays out the results of load testing for band joist headers that have to carry floor loads as well as wall loads. That study helped the officials revising the International Residential Code (IRC) to create prescriptive standards for rim headers, which have now been written into the 2015 edition of the code.
Another Home Innovation Research Labs investigation, into structural bracing for raised heel trusses, hasn't found its way into the code yet. But the observations from that study indicate that raised heel trusses, which allow for much deeper insulation levels over the wall plate in a pitched roof, can be effectively braced against toppling from lateral loads just by extending wall sheathing up onto the vertical heel portion of the truss, rather than with more complicated solid blocking between trusses (see: "Evaluation of the High-Heel Roof-to-Wall Connection with Extended OSB Wall Sheathing," by Andrew DeRenzis, Vladimir Kochkin, and Xiping Wang.)
"In the last few code cycles, more and more of this is showing up in the IRC," says Randy Melvin. Melvin, who is now an independent consultant to the building industry, worked until recently as the director of research and standards for Winchester Homes, a large production homebuilder with operations in Virginia and Maryland, and he spearheaded Winchester's involvement in a field trial of advanced framing methods in cooperation with Home Innovation Research Labs. That research is reported here (see: "Performance Verification of Production-Scalable EnergyEfficient Solutions," by D. Mallay and J. Wiehagen).
"You need to check with your code official," says Melvin. "There are parts of the country that are still back on the 2000 code. Most jurisdictions, if you reference a section of newer code, even though that jurisdiction is on the older code, they will permit you to use the newer section of code. So if you are in a jurisdiction where the structural code is not the 2015 or 2012 or even the 2009 code, frequently if you check with your code official, they will accept newer sections of code, even though that jurisdiction is working off the older code. But you need to check with the authority having jurisdiction."
For Winchester Homes, using advanced framing was the most practical approach to meeting the code — and it positioned the company well for future code advances. At the International Builders Show in Las Vegas, Melvin told a seminar group: "We looked at different systems, and we determined that advanced framing made the most sense because of cost and flexibility, and because it’s a limited departure from what we were already doing. it’s not a big change for the trade base, that’s really critical." After proving the concept in a model home, Winchester moved the methods into production and applied them to all its production house plans.
With the advanced framing advantage, Melvin says, builders can reach equivalent performance to R-20 insulation with an R-19 batt, because of the reduced thermal bridging framing factor. "An R-19 at 24 inches on center easily beats an R-20 at 16," he says. Switching to R-21 batts instead would have resulted in a marginal improvement at a serious up-charge in price; sticking with R-19 batts and improving the framing system saved more energy while also reducing framing labor. And the method future-proofs builders against the next code change: with Owens Corning ProPink L-77 blown-in fiberglass insulation, a 2x6 wall framed at 24 inches on center can achieve R-24.
"So we are good to R24 right away, no problem." Melvin told his Builders Show audience. "But if it goes up beyond that, maybe we could do a couple inches of high density closed cell polyurethane inside and go up, and then eventually, you know, maybe some exterior additional insulation outside. So this is a very expandable system."
