The facing of a faced building insulation assembly includes a central field portion with a selected water vapor permeance rating that is bonded to an insulation layer to provide the faced building insulation assembly with a selected water vapor permeance rating. The facing may have lateral tabs and may be separable longitudinally along separable locations in the insulation layer of the assembly. The field portion of the facing may include a fungi growth inhibiting agent, a pesticide, a coating to stiffen the facing and/or decrease the flame spread and smoke formation characteristics of the facing, and/or a heat activated bonding agent that bonds the facing to the insulation layer of the assembly.