Lightweight composite building panels with incorporated drainage layer that facilitates moisture removal and methods of manufacturing and using lightweight composite building panels with incorporated drainage layer. The lightweight composite building panels with incorporated drainage layer can be used to applied a desired finish to exterior wall and roof structures. The lightweight composite building panels include a core composite panel structure and a drainage layer attached or bonded thereto. The core composite panel structure includes a foam core sandwiched between first and second protective layers, such as a fiber mesh reinforced cementitious composition and/or cured thermoset resin or other rigid material. The drainage layer is designed to face an exterior wall or roof structure to facilitate removal of moisture between the panels and underlying wall or roof structure. The building panels can be cut, drilled, and screwed, nailed, or glued to structural elements of buildings, such as OSB sheathing.

Exterior wall structures or roofing decks include an exterior wall or roof frame and lightweight composite sheathing panels fastened thereto by screws, other mechanical fasteners, and/or construction adhesive. Lightweight composite sheathing panels include a foam core and protective layers formed over and covering the foam core. The foam core may include extruded polystyrene (XPS), other polymer foam material, or inorganic foam material. The protective layers may include a fiber mesh reinforced cementitious composition, a thermoset polymer, or other rigid material. Joints between adjacent composite sheathing panels are sealed using sealing tape, polyurethane foam, and/or other sealant Lightweight composite sheathing panels can be fastened to studs or trusses suing screws, nails, adhesives, and other fasteners known in the art. The exterior wall structure or roofing deck is waterproof, fire-resistant, resists water damage, and facilitates application of finishes such as stucco, brick veneers, stone and masonry, shingles, roofing tiles, and metal cladding.

Exterior wall structures include exterior walls and lightweight composite panels to which an exterior finish is applied. Exterior wall structures may include wooden or metal studs to which sheathing (e.g., OSB panels or composite sheathing panels) are fastened. A drainage layer can be positioned between sheathing and lightweight composite panels to which an exterior finish is applied. Lightweight composite panels are fastened to sheathing and/or studs by screws, nails, rivets, other mechanical fasteners, and/or adhesive. Lightweight composite panels can include a polymer foam core with interior and exterior surfaces and fiber mesh reinforced cementitious layers formed over and covering the foam core surfaces. Joints between adjacent lightweight composite panels can be sealed using sealing tape, mesh tape and a seam coat, polyurethane foam, and/or other sealants. The exterior wall structure is waterproof, fire-resistant, and facilitates application of different finishes, such as stucco, tiles, or stone, masonry, or brick veneers.

Lightweight composite panels, compositions used to make lightweight composite panels, and methods for manufacturing lightweight composite panels. The lightweight composite panels include a lightweight foam core sandwiched between thin protective layers selected from fiber mesh reinforced cementitious layer and thermoset polymer layer, e.g., polyurea or polyaspartic. The lightweight composite panels can be used in place of conventional wallboards and panels, including for various uses such as interior drywall, backer boards for tile and other interior finishes, including those exposed to moisture, exterior sheathing, floor underlayment, soffits, roofing decks, shaft liners, and the like. The lightweight composite panels can be cut, drilled, and screwed onto structural elements of buildings, such as wall frames comprising wooden or metal studs, roof frames comprising boards, studs, or trusses, floor joists, concrete floors, foundations, and the like. Exterior sheathing panels can include a drainage layer and/or a factory installed finish.