Engineered wall systems are an option for your home
By Marcus Renner on 03/16/2006
Most homes today are built using a method called Western platform framing, also called two-by-four, or stick, framing. This type of framing saves time and money but is not the only efficient way to build. In the past 50 years, other wall systems with considerable advantages to our current form of building have been developed and tested. These systems are accepted by building-code officials in most areas of the country.
Stick framing can be done in a more energy-efficient way. Engineers have created a system known as Optimal Value Engineering, or OVE. This idea restructures how a stick-framed wall is built. Studs are configured so insulation can be added in places that usually aren’t insulated well, including exterior corners, intersections of interior and exterior walls, the area where the roof meets the house, around envelope penetrations and behind shower stalls. Ridged insulation also can be used as the exterior sheathing to provide a continuous layer of insulation. OVE also addresses wood use by minimizing the amount used in a home by not overbuilding and placing support wisely. If constructed using the OVE approach, a stick-framed home can achieve substantial energy savings.
Structural insulated panels, or SIPS, are the most popular form of construction after stick framing. The panels are made of foam insulation sandwiched between a “skin” of oriented strand board, or OSB. The foam and wood create a strong wall section that provides a continuous layer of insulation. Few, if any, structural members divide the insulation. The layer of OSB on the two sides also provides a continuous nailing surface for drywall and siding.
The most popular and least expensive foam insulation used between the wood is extruded polystyrene, or EPS, also known as bead board or Styrofoam. When we look at all types of insulation, we use the R-value measurement. The “R” of a material is its resistance to heat transfer. The higher the R-value, the better a material will insulate a home from heat or cold. EPS foam, which is glued to the oriented strand board, has an R-value of about 3.5 an inch. Individual panels can be factory-cut to the specifications of the plans or cut on site. An average home can be erected within a few days.
Polyurethane foam SIPS have insulating foam injected into a mold, which adheres the OSB to the foam. The foam hardens and has an R-value of about 7 an inch. Although this diminishes slightly over time, polyurethane panels are better insulators. The panels are stronger, so there is no need for structural wood in the panel as in EPS structural insulated panels. This creates an unbroken layer of insulation around the envelope of the home.
Insulated concrete form, or ICF, construction uses foam blocks to create a form to pour concrete into. Unlike conventional concrete work, the form stays in place and provides a layer of insulation on either side of the wall. This configuration creates a layer of thermal mass that becomes energy storage because it is insulated on both sides. ICF homes can be 50 percent more energy efficient during the life of the home and much quieter than a common stick-framed house. Concrete walls also make the home stronger and better able to survive severe storms and earthquakes.
About 50 manufacturers make ICF form systems. Most use EPS foam to create the form walls and plastic to separate the foam and create space for the concrete. The blocks are reinforced with rebar and filled with concrete. Some ICFs are made with recycled materials such as mineralized wood chips and recycled EPS foam and cement.
Another engineered wall system that is becoming more popular is a pre-cast concrete wall. On highways you may see wall sections up to 12 feet long that are made at a factory and trucked to the site. The sections then are placed with a crane and bolted together to create the exterior wall of the home. Pre-cast concrete is mostly used for earth-bermed basements and lower floors although it can be stacked three stories high.
The concrete wall is usually 2 inches to 3 inches thick, and the interior of the wall has ridged insulation with an R-value of 12.5. Pre-cast walls typically don’t need a concrete footer as most below-grade walls do. All that’s needed is a gravel trench that allows water to drain away. A slab floor is poured, and drywall can easily be attached to ribs on the interior. The exterior comes finished to look like stucco and can be painted. The wall system can be installed in less than a day and provides an insulated concrete wall with a small amount of concrete.
Autoclaved, aerated concrete, or AAC, uses cement to create a lightweight material filled with tiny air bubbles. The material comes pre-cut in blocks or panels. For residential construction, blocks 8 inches to 12 inches thick are used for walls. AAC provides structure and insulation. Any type of interior and exterior finish can be used, but plaster and stucco are the most popular and easiest.
AAC construction is fast and easy. Common carpentry tools can be used, and the process is quickly learned. The material is easy to sculpt, and architectural details can be adhered anywhere with the gluelike mortar. AAC walls are soundproof because the air bubbles act as thermal and sound insulation. AAC performs best in climates that require more cooling than heating, so your location may affect the walls’ performance.
Each of these engineered wall systems has advantages and disadvantages and should be understood by the builder before deciding whether or not to use them. Keep in mind that a house is a system made up of many other systems. A holistic approach should be taken to understand how the systems interact. Engineered wall systems provide a tighter building. We have to allow the home to breathe through a well-designed passive or mechanical ventilation scheme to avoid moisture buildup on the interior.
Today’s engineered wall systems are usually designed to provide more insulation, a tighter building envelope and a stronger wall than a stick-framed building. These products and methods can save money and the environment.
[Marcus Renner works with Appropriate Building Solutions Inc., a sustainable-construction company in Western North Carolina. He teaches sustainable building classes at Appalachian State University. He can be reached at email@example.com.]