This type of insulation is commonly used to insulate attic spaces. The building code typically requires that the space between batt insulation and a low-slope roof be ventilated to the exterior which creates a myriad of issues related to control of air infiltration out of the ceiling of the spaces below. It is better to avoid the situation all together and use rigid insulation on top of the deck with a water-resistant air and vapor retarder membrane below and cover board or sheathing above. Blanket insulation is commonly used to insulate roofs of pre-engineered metal buildings. Fiberglass insulation is the most common batt/blanket insulation, and it is also available as a blown-in product. Mineral wool is also available in configurations suitable for roofing; it has a higher compressive strength than fiberglass. Cellulose (recycled newsprint) is also a common blown-in insulation. If cellulose is specified, specify a product that has been treated for mold and fire resistance.

Note: Batt insulation is insulation that is factory pre-cut into lengths of approximately 4′, 8′ or 9′ and bundled without rolling. Blanket insulation is insulation that is supplied in a roll.