Can Fiberglass Batt Insulation be Installed in an Unvented Attic?

Unfaced Batts

• Always used unfaced fiberglass batts when adding attic insulation. Facing is a vapor barrier and loose fill insulation is typically installed over a vapor barrier. Doubling vapor barriers will create moisture problems because the second barrier will prevent any moisture from escaping.

Always Vent Attics

• Never install fiberglass batts in an unvented attic. Attics should be properly sealed to prevent outside air from infiltrating, but must be vented to allow moisture to escape. Installing fiberglass batts in an unvented attic will create a build-up of moisture, which can deteriorate the insulation and potentially cause damage to drywall and other components.

What Venting Does

• It may seem odd to say an attic must be sealed against outside air, but vented at the same time. In the winter, venting allows a natural flow of air to keep the attic cold and prevent ice damming, which is snow that melts from a warm attic and then refreezes at the gutter to block water from flowing off. That puddling will damage a roof. In summer, venting allows super-heated air to flow out, eliminating moisture condensation in the attic.

Go Across Joists

• Always install fiberglass batts across the roof joists, not in between. This allows an air gap between the batts and the loose fill and prevents the batts from compressing or condensing the loose fill. Never install batts over recessed light fixtures or soffit vents, which are at the edges of the attic.