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Exterior walls must provide multiple functions including weather and air resistance, energy efficiency, and structure. Most commonly, these functions are met with a combination of materials that are typically individually installed.  Structural insulating sheathing provides a multi-function exterior wall sheathing product that is applied in a single layer and provides additional continuous insulation, a weather- and air infiltration-resistant barrier, and structural wall bracing. The product is a marriage of two proven sheathing materials—foam sheathing (polyisocyanurate) and structural laminated fibrous board with a thermal resistance of R-3 for ½-inch thickness.
Structural insulating sheathing provides a structural method of design for braced wall panel construction, and many additional benefits. Using a single product simplifies wall construction and allows labor savings. It can be installed using common construction tools and skills, and time is saved since it eliminates the installation of a separate layer of building wrap or felt paper for the weather-resistant barrier (WRB). Further, it reduces handling and improves worker safety by replacing two installations with one of a lighter panel weight.
The material fits together with standard components – window and door jambs do not require extension with ½-inch-thick sheathing material. It is more rigid and impact resistant than traditional foam sheathing, and improves energy performance of exterior wall assemblies. Additionally, one manufacturer’s product contains 80 percent post-consumer recycled material.
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Structural insulating sheathing can simplify wall construction by combining energy efficiency, weather protection, and structural requirements into a single product. Labor savings can also be achieved as multiple functions are performed in one product application.
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Insulating sheathing panels provide an R-3 insulating value (larger R-values are available with greater panel thickness) along with the durability aspects. A continuous layer of exterior insulation improves overall thermal performance of a wall assembly and eliminates thermal short-circuits at studs.
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Wall durability is provided through the multiple characteristics of structural insulating sheathing. Sheathing installed with taped edges provides a water-resistive barrier while bracing a building’s framework against eccentric loads caused by wind and seismic activity, and the polyisocianurate foam provides added and continuous insulation outside of the building’s framework.
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Structural insulating sheathing products are installed with techniques and tools that are typically used for the installation of wall sheathing. Pneumatic tools and fasteners must comply with those required by the manufacturer and approved in the manufacturer’s code evaluation data. Used as a water- and air-resistant barrier, panel joints must be taped and properly integrated with flashing of other wall components (e.g., windows and doors) in accordance with manufacturer recommendations.
Structural insulating sheathing is more expensive than traditional sheathing materials such as OSB. However, half-inch thick structural insulating sheathing is competitive with the cost of a wall sheathed in structural wood, plus a WRB applied separately.
An airtight house sheathed with continuous insulation should perform more efficiently in energy usage than a home built with wall cavity insulation only.
DOW Chemical Co.’s structural insulated sheathing product has been submitted for ICC-ES evaluation. Approval is likely in early 2008. Products from other companies are currently in development and review.
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Panels can be installed with roofing nails spaced at 3 inches along panel edges and 6 inches at intermediate locations. Seams must be taped for maximum air and water resistance
One manufacturer offers a 15-year limited warranty covering thermal performance of the product.
Structural insulating sheathing panels provide a single-layer method for improving the energy efficiency of buildings. Structural sheathing, additional continuous insulation outside of the wall cavity, and an air and moisture barrier are available in a single product and installation step. Before the introduction of one sheathing panel that provides all of these features, repetitive applications of sheathing/WRB or custom let-in bracing were required to achieve the same level of performance that is now possible with the application of one product.
Structural insulated panels installed as continuous sheathing with the panel edges taped compare evenly with the combined cost of oriented strand board (OSB) sheathing and a weather resistant barrier (WRB). Beginning in 2006, the International Residential Code (IRC) will require a WRB over OSB for code compliance when using most of the conventional exterior cladding systems. Including the cost of a WRB, tape, and installation to the framer’s scope will add approximately 28 cents per square foot, or $9.00 for a 4’ x 8’ sheet to the cost of a wall assembly for a builder. The additional cost of the WRB pushes structural wood sheathing into the same price range as structural insulating sheathing.
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