Abstract: A core/base layer, an intermediate layer, a divider layer between the core and intermediate layers, and a water-resistant layer on the intermediate layer opposite the core layer. The core and intermediate layers are made of a cementitious material to provide structural-strength and fire-resistance properties, with the core layer including an aggregate material for added strength, the intermediate layer including an hydrophobic additive for water resistance, and the divider layer positioned between the core and intermediate layers to form a physical barrier that prevents cross-migration of the aggregate material and the hydrophobic additive between these layers. The water-resistant layer includes a fiber-based carrier layer with an outward-facing surface having a weather barrier layer secured to it and with an opposite uncoated inward-facing surface having loose fiber strands extending from it and embedded into the intermediate layer to secure the water-resistant layer to the intermediate layer.