Fiberglass batts are commonly used to insulate flat ceilings and attic areas in both new and existing buildings. They offer performance, cost-effectiveness, and relative ease of installation, but that doesn’t mean they’re always installed properly. The performance of any insulation product is dependent not only on selecting the proper product but also on installing it correctly. So, how does one install batts in flat ceilings to maximize thermal performance?

Doing the Job Right

Ceiling batts are easy to install but the installer must take a few precautions to ensure quality application for a flat ceiling. Here are the basics:

1. Use a full-width product that is designed for the width between the ceiling joists (such as R-49). Never use narrow-width materials since the framing members will not be covered.
2. Install batts out over the exterior wall top plates. Batts assure thermal protection at the eaves by preventing cold spots and potential moisture condensation.
3. With eave vents, leave at least one inch of clearance between the insulation and roof deck. Use baffles where needed.
4. Make sure that the ends of the insulation batts butt together snugly. This is easy to accomplish with batt insulation.
5. When installing insulation from below, make sure that the batts are flush with the ceiling line.
6. Don’t cover recessed light fixtures with insulation. Unless the fixture is Insulation Contact (IC) rated, any insulation must be kept at least three inches away.
7. When using faced product, install the vapor retarder down toward the living space. Standard facing cannot be left uncovered and must be covered by drywall, paneling, or other appropriate interior finish. 

Beauty and the Batts

Superior installation of batt insulation is a beautiful thing and doing it right means that the product will achieve expected thermal performance over the life of a building. Minding the details of Grade I installation can also help ensure a HERS-rated home doesn’t get penalized for a Grade II or Grade III installation according to RESNET’s grading system.

For more details on installing batt insulation to Grade I specifications, visit our Grade I installation resources page and take our Grade I installation online training that even comes with a certificate of completion.