A Better Wall for Production Builders
Designing a better wall system isn’t particularly hard. Designing one with a chance of being accepted by production builders, on the other hand, has proven difficult ... and that’s a problem.
Demand for higher-performance wall systems is growing, partly because of more-stringent energy codes. But builders aren’t adopting existing solutions—things like double-wall framing or thick layers of exterior rigid foam over wall sheathing—in significant numbers.
The National Association of Home Builders’ (NAHB) Home Innovation Research Labs is trying to lure more builders into constructing high-efficiency walls with the development of its “Extended Plate and Beam” wall system.
Called EP&B for short, Extended Plate and Beam adapts methods that production builders—who build the majority of American homes—already know. At its most basic, EP&B consists of 2×4 studs between 2×6 top and bottom plates, and the extra 2-in. overhang is filled with rigid foam before structural sheathing is attached with long nails (see drawing right). From there, installing windows, doors, flashing, and cladding is largely the same as for a regular 2×6 wall.
The main advantage to production builders? Installing OSB or plywood outboard of the rigid foam removes the need for furring strips.
EP&B vs. other walls
According to calculations made by the Home Innovation Research Labs, the EP&B system costs less to build than either a 2×6 wall with continuous exterior rigid foam or a double-stud wall.
In its most basic configuration, an EP&B wall with 2 in. of extruded polystyrene (XPS) foam and R-13 fiberglass batts has a nominal R-value of R-23. That’s a 77% increase in R-value from a conventionally framed 2×4 wall with the same R-13 batt insulation and no foam.
Analysis published by the United States Department of Energy (DOE) estimates the cost of this particular wall assembly at $21.12 per sq. ft. of framing when sided with fiber cement—$2.18 more than a regular 2×4 wall, including materials and labor. In other words, for an 11.5% premium, they…