High-Performance Walls: Page 2 of 6

For Energy-Efficient Building
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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

I-Joist Walls
Repurposing Floor Joists for Superinsulated Houses

Walls framed conventionally with dimensional lumber have two big energy-efficiency problems: there’s not enough room for insulation, and there’s a good deal of thermal bridging—heat transfer through the framing. But modern techniques are addressing those issues.

The Passivhaus concept. Katrin Klingenberg found a way around both of those issues and designed a house in Urbana, Illinois, to the performance standards of Germany’s Passivhaus Institute. Instead of framing with dimensional lumber, she used 12-inch-deep I-joists for the walls and wrapped the outside with a 2-inch layer of rigid foam insulation. Wall cavities were filled with blown-in fiberglass for about R-60. Walls were balloon-framed, meaning the I-joists run uninterrupted from the foundation to the top plate, eliminating heat loss through a rim joist between floors.

I-joists are usually used in floor framing, not walls. But their thin webs of oriented strand board reduce thermal bridging, and their depth provides lots of room for insulation. I-joists, however, aren’t as stiff as dimensional lumber, and using them for wall framing requires a slightly different technique. Both sides of the I-joist, for example, need structural sheathing to prevent their flanges from bending or flexing.

Klingenberg, the executive director of the Passive House Institute US, no longer uses I-joists as weight-bearing components in walls. Instead, she builds structural 2-by-4 walls, sheaths them with OSB, and bolts I-joists to the outside. “It’s easier to get inspectors to sign off this way,” she says.

Larsen trusses. I-joist walls are similar to Larsen trusses, developed by Edmonton, Alberta, builder John Larsen in the early 1980s. Like the newer I-joist technique, Larsen trusses do not carry any of the roof loads. They can be made on site with 2-by-2s that are connected by small gussets of 3/8-inch plywood. When completed, the truss looks something like a ladder. Trusses are attached to the outside of sheathing that covers a 2-by-4 or 2-by-6 wall, and then sheathed on the outside before the siding is applied. Wall R-values can easily top 40.

Larsen says the trusses arose as a faster alternative to a double stud-wall design. Houses built with Larsen trusses are not only well-insulated but also can be very tight; one 4,500-square-foot house had an air-leakage rate of only 0.80 ACH at 50 pascals—almost “tight” enough to meet very stringent Passivhaus standards. An air barrier applied over the sheathing is less likely to have penetrations in it. Also, dense-pack cellulose at that thickness, while not technically an air barrier, is a lot more effective compared to something like fiberglass batts.

One advantage of this method is that trusses can be built on site from relatively low-cost materials. Blown-in fiberglass or cellulose costs less than sprayed polyurethane foam, but at 10 inches or 12 inches thick makes high R-values and low thermal bridging. On the down side, these extra-thick walls require special detailing for doors and windows.

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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