Four primary causes: inadequate moisture management (no drainage plane behind siding traps moisture with no exit path, causing sheathing rot and mold — the most common hidden failure); improper flashing at windows, doors, and transitions (the most common water infiltration entry point — visible as staining at window corners); UV degradation without maintenance (fiber cement and wood left unpainted absorb moisture and decay); and WUI non-compliance (vinyl in fire zones creates liability beyond material performance). RainFire Builders addresses all four: drainage plane as standard, metal flashing at all transitions, ColorPlus or site-applied top coat at installation, and WUI material verification before any material is selected.