Using sheathing that combines rigid foam with OSB is a good way to tighten the building envelope and meet new code R-value requirements with a standard stud wall. Unlike other systems, ThermalStar One panels from Universal Forest Products (UFP) are designed to be installed with the OSB against the framing, which means they can be fastened with standard spacing using standard-length nails.
As with other panelized sheathing systems, nailing through a thickness of foam requires use of a modified nail gun. UFP collaborated with Senco to produce guns that work with a regular compressor but are equipped with longer driving pins to set the fasteners at the proper depth. The guns also have a wider foot with an improved sightline, which enables accurate fastening without damage to the foam. The company also makes a depth gauge that installers—and inspectors—can use to confirm proper nailing depth.
The panels combine 7/16-inch OSB with a layer of EPS (expanded polystyrene) foam impregnated with graphite, which acts as a radiant-energy reflector for improved R-value. The foam is capped by a 3-mil polymeric film that qualifies as a water resistant barrier and is rated for six months’ UV exposure.
With a compressive strength of 15 psi, the EPS layer is available in three thicknesses, with insulating values of R-3, R-5, or R-7.5; the OSB layer adds another R-0.6, yielding three nominal panel thicknesses of 1 1/8, 1 ½, and 2 inches, respectively. The panels qualify as a Class II vapor retarder (<0.3 perms) and are available in 4x8 and 4x9 sheets (4x10 panels can be special-ordered).