An insulation assembly includes an elongated batt of fibrous insulation material having two opposed major surfaces, where the batt has a first facing secured on its first major surface. The first facing extends beyond the side edges of the batt to form opposed flanges suitable for attaching the insulation assembly to a building structure. The batt has a second facing secured on its second major surface, with the second facing extending beyond the side edges of the batt to form opposed flanges suitable for attaching the insulation assembly to a building structure. The method of making an insulation assembly includes moving a pack of fibrous insulation material along a path, where the fibrous insulation material has two opposed major surfaces. A continuous encapsulation material is applied to the pack, and a portion of the encapsulation material is continuously gathered to form a two part fold. The two parts of the fold are bonded together to form a flange suitable for attaching the insulation assembly to a building structure.