High-Performance Walls: Page 6 of 6

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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

Foam ICFs. Several kinds of foam are used to make most concrete forms, including EPS (the most popular), XPS, and expanded polyurethane. A typical EPS form consists of two parallel sheets of foam separated by plastic or metal webbing. Blocks are stacked together to form walls. Builders add steel rebar and then pour concrete into the forms. Foam ICFs are available in fully assembled blocks or as ready-to-assemble components that are shipped flat.

The R-value of the blocks depends on foam type and foam thickness. EPS, for example, is about R-4 per inch, while XPS is rated about R-5 per inch. Polyurethane foam used in ICFs is about R-6 per inch. The concrete inside an ICF wall contributes virtually nothing to its insulating qualities. Forms are available in a variety of widths to produce concrete cores from 4 inches to 24 inches or more. Thicker walls are stronger because of the increased concrete content, but are not necessarily better thermal insulators.

ICF construction has some advantages—high strength and low rates of air infiltration are two important ones—but overall wall R-values aren’t as high as with some of the alternatives. In fact, the material used to make some types of ICFs—polystyrene beads and cement or wood chips and cement—have lower per-inch R-values than rigid foam, sprayed-in foam, or even dense-pack cellulose. That makes it difficult to get the R-values that high-performance buildings often specify—R-40 in the walls and R-60 or more in the ceiling. As a result, builders might consider ICFs for the foundation but choose another option for above-grade walls, such as wood-frame construction with both cavity insulation and a layer of rigid insulation over the sheathing. ICFs made with EPS foam are relatively effective thermal insulators, but it would still take 10 inches of foam— 5 inches on each side of the concrete core—to equal R-40.  

Insulation
On the Outside

One of the most radical high-performance wall systems is the “pressure equalized rain screen insulated structure technique” (PERSIST), developed by the National Research Council of Canada in the 1960s. Walls are framed with 2-by-4s without any roof overhangs, sheathed with plywood or OSB, and covered with a peel-and-stick membrane, such as Grace Ice & Water Shield (a rubberized asphalt adhesive backed by a layer of high-density cross-laminated polyethylene). Then the building is wrapped in one or more layers of rigid foam insulation, which in very cold regions could be as much as 8 inches thick. Using XPS foam at that thickness would mean walls of R-40. The membrane provides an effective air and vapor barrier and, because it’s installed on the warm side of the insulation, does not foster condensation inside the walls.

Builders apply strapping over the foam on the walls and attach the siding to the strapping. This creates what’s called a “rain screen.” Any water that is forced through the siding (in a driving rain, for example) drains away, and the back of the siding dries more effectively, which extends siding life. On the roof, sleepers—2-by-4s on the flat—are installed over the rafters, followed by a second layer of sheathing. Rakes and eaves are applied.

Houses built this way are extremely resistant to air leaks, with greatly reduced thermal bridging, and the insulation-free stud cavities are excellent places to run wiring or plumbing without interrupting the air barrier. On the down side, all that membrane and the layers of rigid foam are expensive—and there’s extra time involved in detailing the doors, windows, and roof overhangs.

The PERSIST is effective in all climate zones, not just the far north. A similar approach called residential exterior membrane outside-insulation technique (REMOTE) uses almost the same wall system but a more conventional unconditioned attic. As explained by the Cold Climate Housing Research Center (CCHRC) in Fairbanks, Alaska, REMOTE eliminates the need to build a second roof. It also calls for the addition of cavity insulation in the framed wall, with one-third of total wall insulation on the warm side of the membrane and two-thirds on the outside. (Note that this ratio of inside to outside insulation would be dictated by climate to keep the dew point to the exterior of the vapor barrier).

Given the design, air leakage rates can be very low. A blower-door test of a REMOTE house by the CCHRC showed air tightness at 0.4 ACH50 (air changes per hour at 50 pascals of pressure, a standard industry measure). This is an extremely low number, and about one-fifth the leakage of a conventionally built comparison house. In the CCHRC house, building costs were about $0.85 more per square foot of heated space than a conventionally built house, including labor. Keep in mind that cost differences depend on a variety of factors, and that this side-by-side comparison took place more than 10 years ago, so costs are out of date.

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Scott Gibson co-authored Green from the Ground Up and Toward a Zero Energy Home (The Taunton Press). He is a contributing writer at Fine Homebuilding magazine, and at GreenBuildingAdvisor.com. Scott and his wife live in southern Maine.

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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