Interior Fiberglass Vs. Sheathing Insulation

Fiberglass

• Fiberglass insulation is usually pink or yellow in color and is available in blanket-like batts that you roll onto interior surfaces such as floors or nail to walls and ceilings. It is made of glass that has been spun into long fibers, which are then woven and coated with a material to bind the spun-glass fibers together. Fiberglass grew in popularity during the 1960s as a “safe” alternative to asbestos. As with many insulation materials, some people have concerns about fiberglass in terms of potential health risks for those with allergies and its possible links to cancer. As a result, some people choose not to use fiberglass inside duct work for heating and ventilation systems, and instead focus on restricting its application to sheathing materials used for floors, walls and ceilings, which do not connect to ventilation channels in homes and buildings.

Sheathing

• Sheathing is the term used to describe the layer of materials that covers the exterior surface of the frame of a home or building. Common sheathing materials include plywood and fiberboard. Insulation materials, such as fiberglass, polystyrene and foil-faced polyisocyanurate, are also forms of sheathing materials when applied to exterior walls. Sheathing materials stabilize the frame of the building and provide a surface for attaching the final exterior material, such as wood or vinyl siding or masonry materials on walls and roofing materials. Sheathing also forms an insulation-type barrier to prevent heat loss by blocking air from entering through the exterior walls of a building.

Similarities

• Insulation and sheathing are components of what is referred to as the “envelope” of a home or building. The envelope includes every type of material used to assemble the exterior and interior walls. Each component — including the fiberglass and sheathing — has what is called an “R-value.” This numeric value rates the material for its insulation capacity to keep warm air in and cool air out of the building. For example, the R-value for 1/2-inch plywood sheathing is 0.63, and the R-value of 3-½-inch batt fiberglass insulation is 11.00, according to Colorado Energy.org. The combination of the two materials would contribute 11.63 to the total R-value of the home’s wall assembly.

Differences

• Fiberglass is an insulation material, and sheathing is a structural material. Fiberglass is primarily used on interior walls, while sheathing is primarily used on exterior walls. Fiberglass, by nature, has a higher R-value than sheathing because as an insulation material it is designed to contribute to the overall energy efficiency of a building. Sheathing, on the other hand, helps define the shape and structure of a building, so it has an entirely different purpose from fiberglass insulation.