How to Install Baffles on the Underside of Rafters

Rafter vent baffles keep air flowing properly through the attic.

You must install cardboard vent baffles under rafters when you have vented soffits -- especially if using blown insulation. Baffles keep insulation from falling into the soffit, which blocks airflow and causes moisture buildup -- and potentially mold and ruined insulation. Installing baffles on the rafters after the upstairs ceiling is in place involves wedging yourself into the tight space where the rafter meets the sill plate, so the job will become easier if you have a helper. Baffles come in standard 16- or 24-inch sizes depending on the distance between your rafters; measure before going to the store. Lay boards across truss chords or ceiling joists to keep from falling through the ceiling.

Things You'll Need

• Construction-grade staple gun
• 1/2-inch staples
• Razor knife or scissors

Instructions

1. Rake back any blown-in insulation that has fallen into the soffit space, or pull fiberglass batting out of the way.

2. Fold the sides of a cardboard baffle downward, and place it between two rafters with the folds down. The bottom edge of each cardboard baffle should rest on the sill plate (or as close as possible).

3. Staple the rafter vent every 4 inches with a construction-grade staple gun for a good hold. Allow at least 1 inch between the baffle and the roof sheeting.

4. Continue to install full-size attic baffles along both sides of the house. Use a razor knife to trim a baffle if you encounter a rafter space smaller than standard.

Tips & Warnings

• Long sleeves, long pants and proper shoes are a must to protect your body from insulation fiberglass.

• Wear a protective mask whenever you work around fiberglass insulation.

References

• Install Attic Baffles and Vent Chutes
• U.S. Department of Energy: Insulating and Ventilating Attics

Resources

• Heating-and-Cooling: Attic Ventilation Basics