A fire resistant fibrous composite article includes fibers bound together into a consolidated fibrous article such as a fiberboard. A first fire retardant composition including a hydrated mineral is in the interior of the article. A second fire retardant composition including a boron-containing compound is in the surface of the article. In another embodiment, a fire resistant fibrous composite article includes fibers, a fire retardant hydrated mineral and a zeolite bound together into a consolidated fibrous article which is resistant to water absorption. Another embodiment provides a lignocellulosic fibrous composite board for use in a roof system in which the board is exposed to bonding energy when it is bonded to another roof system component during construction of the roof. Another embodiment relates to a roof system of which a lignocellulosic fibrous composite board is part. The board or the roof system is in compliance with one or more fire resistance or flame and smoke standards. A further embodiment relates to a method of installing a fibrous composite board in a roof system.