High-Performance Walls: Page 4 of 6

For Energy-Efficient Building
Beginner

Inside this Article

Walls using structural insulated panels (SIPs).
The walls of this home, which are constructed with structural insulated panels (SIPs), combine the framing, insulation, and sheathing into one unit, providing faster assembly and a thermally efficient envelope.
Traditional framing
Traditional framing often results in thermal bridging and excess wood use.
Raised heel roof trusses
Raised heel roof trusses allow more attic insulation in the space between the wall top plate and roof.
I-Joist wall construction before insulation
Klingenberg’s I-joist solution, before wrapping with rigid foam insulation.
I-Joist wall construction after insulation
Klingenberg’s I-joist solution, after wrapping with rigid foam insulation. Furring strips screwed to the I-joist flanges through the foam provided a vented rain screen and a place to attach the siding.
Structural Insulated Panels (SIPs)
SIPs are custom-fabricated in a factory and then shipped via truck to the building site. There, panels are typically set in place by a boom truck.
Structural Insulated Panels (SIPs)
Panels arrive on the job site ready to assemble, allowing faster construction times than are possible with conventional framing.
Trimming straw bales
A bale knife can be used to trim straw bales for windows and doors, or to aesthetically round wall corners.
Applying the stucco
Applying the protective stucco outer coat. The wire mesh keeps the stucco from breaking away from the wall.
Bales used as infill walls
Lengths of rebar help keep bales aligned. These bales are infill walls, with the load-bearing structure already in place.
Window framing in a double-stud wall
Door and window framing in a double-stud wall is more complex compared to standard framing.
Double-stud walls: aligned studs
One approach to double-stud walls: Separated by a gap that will be filled with insulation, aligned studs help minimize thermal bridging.
Double-stud walls: staggered studs
Another approaches to double-stud walls: Separated by a gap that will be filled with insulation, staggered studs help minimize thermal bridging.
Durisol Insulated Concrete Forms (ICFs)
Durisol ICFs, ready to receive concrete.
Rastra ICF panels
Larger Rastra ICF panels require heavy equipment to lift.
ICFs rest on continuous poured-concrete footings.
Like many other wall systems, ICFs rest on continuous poured-concrete footings.
ICFs consist of two outer layers of rigid foam insulation separated by metal or plastic webbing
ICFs consist of two outer layers of rigid foam insulation separated by metal or plastic webbing. After reinforcing steel is added, the forms are filled with concrete.
Residential exterior membrane outside-insulation technique (REMOTE
The REMOTE building technique being applied. Note the waterproof barrier under the layers of rigid foam.
Walls using structural insulated panels (SIPs).
Traditional framing
Raised heel roof trusses
I-Joist wall construction before insulation
I-Joist wall construction after insulation
Structural Insulated Panels (SIPs)
Structural Insulated Panels (SIPs)
Trimming straw bales
Applying the stucco
Bales used as infill walls
Window framing in a double-stud wall
Double-stud walls: aligned studs
Double-stud walls: staggered studs
Durisol Insulated Concrete Forms (ICFs)
Rastra ICF panels
ICFs rest on continuous poured-concrete footings.
ICFs consist of two outer layers of rigid foam insulation separated by metal or plastic webbing
Residential exterior membrane outside-insulation technique (REMOTE

Bale walls can be load-bearing (“Nebraska style”), or used as infill for a timber- or stick-frame that carries roof loads. Bales are stacked flat or on edge between framing members (for infill construction) atop a conventional concrete stem wall, and then finished with earthen or lime plaster, or cement stucco, to protect the building from the elements. Window and door openings are created with wood frames. For load-bearing walls, bales are typically compressed under a top plate to distribute the weight and help prevent uneven settling. In the original Nebraska straw bale homes, roof loads were evenly distributed around the perimeter of the building with hip roofs, and window sizes were limited. Infill designs are well-suited to complex house shapes. Straw is resistant to rot when protected from rain and snow, and is fire-resistant because its density limits combustion air (likened to trying to burn a telephone book).

Given their thickness, straw bale walls should have higher R-values and less thermal bridging than wood-framed walls insulated with fiberglass or cellulose. In tests at the Oak Ridge National Laboratory, a 19-inch-thick straw bale wall had an R-value of 27.5, or 1.45 per inch. By comparison, a 2-by-6 wall insulated with standard fiberglass batts (and no exterior insulation) would have an R-value of roughly 20 at the center of the wall (less when thermal bridging is taken into account for a whole-wall measurement).

Straw bale construction is not covered in the International Residential Code, meaning that prospective builders need approval from local code officials.

Double-Stud Wall Construction
Standard Building Techniques & Materials

Building a double-stud wall is an easily understood approach to achieving an energy-efficient envelope, using the same techniques and materials that go into a conventionally built house. Two parallel-framed walls are framed from dimensional lumber—one load-bearing and the other a nonweight-bearing partition. The walls are separated by a gap and studs in the two walls can be staggered—or not. Then the wall is filled with insulation, which could be cellulose, fiberglass batts, or something else, which can result in R-40 or above.

This strategy is simple and effective, and used on many high-performance houses, including a Habitat for Humanity house in Wheat Ridge, Colorado, that was designed by Habitat and the National Renewable Energy Laboratory. These designers had two goals: create a net zero-energy home, with the house producing as much energy as it used each year, and have Habitat volunteers build it, not professionals.

The designers spaced the two 2-by-4 walls 3 1/2 inches apart. Fiberglass batts were installed vertically in both stud walls, with a third layer of batts placed horizontally in the space between the two walls. Even though fiberglass batts can be one of the least-effective types of insulation when poorly installed in a conventionally framed house, they proved highly effective here.

Other builders might construct the outer, load-bearing wall from 2-by-6s, for example, to give even more room for insulation. The gap between the two walls eliminates the path for thermal bridging, so double-stud walls don’t need a layer of rigid foam insulation over the sheathing, which simplifies construction considerably while holding costs down.

A trade-off is that some floor space is lost to the second framed wall. In houses with very small footprints, this could be an issue. And, since the framing is duplicated, it doubles the amount of time it takes to frame the house. Applying advanced framing techniques reduces the amount of lumber and construction time. Finally, because of the extra wall depth, detailing doors and windows is a little more complicated. Windows set to the outside of the wall require extra-deep jamb extensions, and some builders flare window openings so walls don’t look too thick, which is also an extra step.  

Comments (3)

Fred Golden's picture

I think that SIPS are the way to go. From poured concrete foundation to enclosed roof in one week! That is pretty good, and almost a requirement in the northwest where rain is frequent, and dry construction timing is short and in-frequent.

zap101's picture

Great article! Double stud walls but no mention of making the inner non load baring wall out of steel studs Why?

lavardera's picture

No discussion of high-performance walls is complete without considering scandinavian building practices. They build stud framed houses just like we do, and achieve very high performance levels using simple techniques that any American builder can follow. No special materials, no special skills, predictable cost and labor time. We've posted detailed information for builders. There is a video series that gives a brief overview:
http://www.youtube.com/watch?v=yZ0W...

And a detailed description of wall types is offered here:
http://blog.lamidesign.com/p/usa-ne...

But its not all about the wall assembly. The framing method is just as important, and in Sweden they have modified the western platform frame for better performance. Much more effective than so called "advanced framing", Swedish Platform Framing fixes the all the weak performance of the platform framing method.
http://blog.lamidesign.com/p/swedis...

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