What Is Insulated Sheathing?
Insulated sheathing is a type of exterior wall sheathing composed of foam insulation laminated onto OSB or plywood. The one-step installation provides structural strength combined with added wall insulation up to R-12.
How Insulated Sheathing Works
Traditional home construction involves nailing or stapling plywood or oriented strand board (OSB) to the exterior of the framing studs. Rigid foam board insulation is often applied over the sheathing to increase R-value and reduce thermal bridging.
Insulated sheathing is an all-in-one application. The foam side of the boards faces the studs with the wood facing out. All joints are then sealed with special tape or liquid to seal all gaps. When properly installed, most brands of insulated sheathing provide structural sheathing, insulation, a water-resistant barrier, and an air barrier in one product.
At least one company (rok-on.com) makes panels with OSB on both sides of the foam–like structural insulated panels (SIPs). This design prevents compressing the foam during installation and adds structural strength.
Insulated sheathing is an ideal product for exterior wall and roof sheathing. It is not suitable for below-grade applications because the OSB is not properly treated to withstand constant moisture.
Types of Insulated Sheathing
Insulated sheathing is manufactured using various types of rigid board insulation. R-values range from R-4.0 to R-12.0 per inch. Panels are 1” thick to 2 ½” thick. They are four feet wide and available in multiple lengths.
Many manufacturers will custom-produce panels using different types and thicknesses of plywood or OSB for special applications. Such as fire ratings and enhanced strength. The most common types of insulation include:
- EPS. Expanded polystyrene insulation–often called beadboard–has an R-value of approximately R-4.0 per inch.
- XPS. Extruded polystyrene insulation–often called Styrofoam–has an R-value of R-5.0 per inch.
- ISO. Polyisocyanurate insulation is foil-wrapped and has an R-value of R-6.5 per inch.
Pros:
Insulated sheathing manufacturers claim their products meet all building codes. R-value requirements vary depending on climate zones. Some of the other benefits include:
- Installation. Installs like normal uninsulated sheathing. Fasteners must extend at least one inch into the framing. All seams, holes, and gaps must be sealed with approved tape or liquid sealant to maintain moisture barrier.
- Moisture. Waterproof when properly sealed.
- Mold. Mold and mildew resistant.
- Impact. Impact resistant.
- Pests. Pest and termite resistant.
Cons:
Insulated sheathing is an attractive time-saving product that adds R-value and saves on energy costs. Before choosing insulated sheathing for a construction project, potential problems need to be considered.
- Moisture and Drainage. Insulated sheathing sealing tape is only warranted for 30 years. Failed adhesion allows moisture and water leakage to penetrate the building envelope.
- Water Resistance. OSB may last less than 60 years before allowing water absorption. Water trapped between the OSB and siding may cause rot. Plywood can delaminate over time but it is still a better choice.
- Roofing Warranties. Some roofing manufacturers will not warranty their products if installed on OSB because of reduced nail-holding ability compared to plywood and dimensional lumber.
- UV Deterioration. All polystyrene products deteriorate in sunlight. Foam edges can deteriorate and become powdery if left exposed too long. The powdered foam rubs off and reduces the R-value at the seams.
Most of these concerns can be easily overcome by using plywood insulated sheathing, covering the sheathing with house wrap before installing siding or stucco, and protecting the product before installation.
Cost of Insulated Sheathing
Insulated sheathing initial costs are higher than OSB sheathing and XPS purchased individually. Using insulated sheathing saves on labor costs, time, and material waste–making the final cost about equal.