Do I need attic baffles in every rafter bay?
Short answer. You need a baffle in every rafter bay that has a soffit or eave vent opening below it and insulation that could block the airflow. With continuous soffit venting that usually means every bay; bays with no vent opening below, or bays where insulation cannot reach the eave, may not need one.
What a baffle does
A baffle, also called a rafter vent or vent chute, is a channel of foam, cardboard or plastic fastened to the underside of the deck at the eave. It holds insulation back so outside air can pass from the soffit into the attic. The residential code requires at least 1 inch of space between insulation and the roof sheathing at the vents, and baffles are the usual way to keep it.
When every bay needs one
- Continuous vented soffit or a continuous strip vent along the eave.
- Blown insulation, which drifts and settles into every corner.
- Vaulted or cathedral ceilings, where each bay is its own vent channel from eave to ridge.
When you can skip some
- Individual undereave vents with solid soffit in between: only the bays over a vent need a baffle, though many installers do every bay anyway for future flexibility.
- Bays blocked by framing, such as at a gable end or above a wall with no eave.
Installation tips
- Push the baffle down far enough to sit past the top of the wall, so insulation cannot spill over the end.
- Add a dam or blocking at the bottom so blown insulation does not wash into the soffit.
- Staple it to the deck, not just tuck it in.
- Work from the attic in the cool of the morning, or have it done during a reroof when some installers can reach the eaves from outside.