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Frame a Home for Energy Efficiency (House Framing for Energy Efficiency)

Construction How-To, Energy Efficiency, Framing September 7, 2010 admin


 

 

Frame a New Home or Addition for Energy Efficiency.

 

 

Anyone contemplating an energy-efficient room addition or building their own home has likely given careful thought to the insulation. Which material is best? What thickness should be used? Is the R-value sufficient? But often they ignore the structural framing, which holds everything together. It doesn’t matter how good the insulation is if air leaks around it; the design and placement of the studs, joists, headers and other framing members affects how well the insulation can do its job.

Framing techniques your grandfather didn’t know, and your dad may not have taught you, can help reduce heating and cooling costs—and use less wood. The trick is to lay out the framing in ways that help eliminate gaps in the insulation and that lessen the number of thermal bridges through the framing members. While not difficult to build, these methods require advanced planning. Your building material dealer may be able to assist with software that can turn a basic home plan into detailed drawings showing energy-efficient framing.

 

Advanced Framing Methods

The National Association of Home Builders (NAHB) developed so-called “advanced framing” methods (also known as “optimum value engineering” or OVE) several decades ago. Don’t let the names frighten you. The practices are relatively straightforward, just different from how framing is traditionally constructed. They include (Figure 1):

• 2 x 6 studs at 24-inch on-center (OC) spacing

• Two-stud corners

• Ladder blocking at wall junctions

• Double rim board and insulating foam in lieu of headers

• In-line framing

• Single top plate

• Minimal trimmers or jack studs

As an example of the potential benefits of these methods, iLevel by Weyerhaeuser built a 24-inch OC demonstration wall with 2 x 6 studs that achieved an 86-percent increase in insulation volume and a 58-percent increase in the wall’s overall R-value, compared to a traditional 2 x 4 wall at 16-inch OC spacing. Further, the demonstration wall used 8 percent less wood volume. The U.S. Dept. of Energy estimates that advanced framing can reduce annual heating and cooling costs up to 5 percent, and for a 2,400-square-foot house, save up to $1,000 in materials.

 

Plan View; 3-stud corner using SBS.

Plan View; 3-stud corner using SBS.

 

2 x 6 Studs at 24-inch OC Spacing

Increasing stud spacing from the standard 16 inches OC to 24 inches increases the overall insulation in the wall cavity, as well as reduces the thermal bridges through the wood since fewer sticks are involved. Interestingly, the use of 2 x 6’s at 24 inches OC versus 2 x 4’s at 16 inches on center provides the necessary structural support using a similar volume of framing material. Yet, the wider spacing enables fewer interruptions in the insulation, while the deeper studs allow for two more inches of insulation between the outside and inside walls.

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As with all advanced framing techniques, be sure to check local code requirements. In some instances, wider stud spacing is not allowed in areas with high winds or earthquakes. Your building material dealer or manufacturer may be able to assist with alternative framing approaches, such as pre-fabricated wood shear braces that can provide the necessary bracing while maintaining a narrow footprint within the wall.

Two-stud plan with L-type junction.

Two-stud plan with L-type junction.

 

Two-stud Corners

Corners typically involve three studs set back-to-back to create nailing points for the exterior sheathing or siding and interior drywall (Figure 2). However, using two studs placed perpendicular to one another provides the necessary structural support, while enabling attachment of the sheathing (Figures 3 and 4). For the drywall, one of the studs provides the nailing point for the material on one wall, and the material for the intersecting wall is attached with a drywall clip. This approach allows insulation to penetrate farther into the corner, instead of leaving gaps and a large thermal bridge created by multiple studs. Plus, it saves on material by eliminating one extra stud at each corner.