Oriented strand board (OSB), with a thin layer of low emitting aluminum foil attached to one side, is a common type of thermal-radiant-barrier sheathing. Foil-backed OSB is applied mostly in attics; however, it is also used in wall systems. The goal of a foil-backed OSB is to cool the air within the top layer of insulation in the attic or wall by emitting the radiant heat absorbed through the roof or exterior walls, which reduces the Delta-T and lessens the overall energy use in a building.
Delta-T is the difference between the temperature of the top layer of insulation in the attic or wall system and the living spaces. For example:
During the hot summer, the heat of the sun can raise the temperature of the top shingles of the roof to nearly 180 degrees. The bottom of the roof deck will be 20 or 30 degrees lower.
Through the process of infrared radiation, the heat from the roof is emitted (or radiated) into the attic where the insulation absorbs it. When this occurs, the top surface of the insulation can reach a temperature of 130 degrees and more, which is much higher than the temperature in the living spaces (68-70 degrees). The Delta-T is the difference in temperature between the top layer of the insulation and the living spaces.
The foil layer of the OSB lowers the Delta-T because the foil is low emitting and does not emit or absorb heat. So, when the sun hits the roof and radiates into the attic or wall, the foil layer of the OSB sheathing reflects the heat to the roof or exterior wall, which keeps the top layer of the insulation just a few degrees warmer than the outside air temperature. Similarly, when heat rises into an attic during cooler months, the foil layer reflects it into the living spaces of a building. Without the foil layer, the OSB sheathing will absorb heat and radiate it into the attic space in the summer, or outside during the winter.
Adding more attic ventilation will help, but not much. Even with excellent airflow in an attic, the temperature of the top surface layer of the insulation will only drop a few degrees.
A better thermal barrier to foil-backed OSB is Barricade Thermo-Brace® S.I.B. Specifically, Thermo-Brace® S.I.B, with weather resistant barriers on both sides, is more moisture resistant and limits thermal conduction and convection more effectively than foil-backed OSB. Importantly, the installation of Thermo-Brace® S.I.B saves builders time and labor over foil-backed OSB.
Thermo-Brace® S.I.B. creates a superior thermal barrier compared to foil-backed OSB barriers. Barricade Thermo-Brace® S.I.B. has high thermal resistance and low thermal conductivity; both features essential to controlling air and moisture infiltration into a wall system.