Fiberglass Sheathing refers to gypsum panels with fiberglass mat faces. Fiberglass sheathing is considered to have superior moisture and mold resistance in comparison to paper face only sheathing. Fiberglass sheathing is primarily used on exterior walls and is an acceptable substrate for just about any material type. It is perhaps most commonly utilized as a substrate for Stucco and EIFS systems. It is also used with brick, shingles, shakes, vinyl, metal, wood, and fiber cement. Fiberglass sheathing is also able to resist destructive winds and flying objects better than some other cladding systems. Commonly sold and utilized thicknesses are 1/2″ and 5/8″ with 5/8″ often being considered and marketed as fire-resistant. Stock sheets commonly come in 4×8, 4×9, and 4×10 but can be had in custom sizes as well. Fiberglass sheathing is also popular for being moisture resistant during installation, more so than plywood or OSB. It is also more resistant to delamination, deterioration, sagging, and warping. It weighs approximately 10-13% more than gypsum sheathing. It can be installed vertically or horizontally with fasteners driven flush with the surface, and 3/8″ or more away from any edge. The following are fastener types commonly recommended with fiberglass sheathing depending on the substrate:
Applied on heavy gauge steel (18 gauge or thicker) – Bugle head fine thread drill point drywall screw – 1″ – 1-1/4″
Applied on light gauge framing (20 Gauge or thinner) – Bugle head fine thread drill point drywall screw – 1″ – 1-1/4″
Applied on wood framing – Bugle Head course thread sharp point screw OR 11 gauge galvanized nail
When aapplied horizontally, fiberglass sheathing should have staggered end joints, with those ends joints fitting snug. It should be 7″ or more above final grade in weather-protected siding systems, and 12″ or more for crawl spaces. If a control joint system is required it will typically be designed by the architect or engineer. Framing behind fiberglass sheathing and most substrates can be 24″ on center, but for EIFS 16″ OC framing is recommended. Fastener spacing should be 8″ On Center. Fiberglass sheathing is also a very popular substrate for soffit sheathing. Soffit framing behind should be 16″ On Center for 1/2″ thick soffit sheathing and 24″ On Center for 5/8″ thick.
It is also recognized as a suitable substrate for Water and Air Resistant Barrier applications. The likes of spray polyurethane foam, self-adhered sheets, fluid applied membranes, and mechanically adhered flexible sheets. Joint protection can be implemented by troweling a bead of sealant to the joints, 2″ wide x 1/16″ thick with a mesh joint tape.
Fiberglass sheathing fire-rated (5/8″) can be used as an adequate replacement for Type X Fire Rated gypsum, but should not be used as roof sheathing, interior/exterior tile backing, or below grade purposes.