What are soffit vent insulation baffles, and do I need them?
Short answer. Insulation baffles, also called rafter vents or vent chutes, are channels installed between the rafters at the eaves that hold insulation away from the underside of the roof deck so air from the soffit vents can flow up into the attic. You need them in every rafter bay that has soffit intake, and the residential code calls for at least 1 inch of air space between insulation and the deck at the vents.
Materials
- Rigid foam: common, inexpensive and easy to staple.
- Cardboard or paper: cheap, but can sag if it gets damp.
- Plastic: durable and moisture resistant.
- Site built from foam board: used in cathedral ceilings for full-length channels.
Installation basics
- Install from the attic before adding insulation, in each bay that has an intake vent.
- Start the baffle at or just past the top of the exterior wall, over the soffit.
- Staple it to the underside of the deck without crushing the channel.
- Run it up past the point where the insulation will reach full depth.
- Add a dam at the bottom, a block or board that keeps insulation from spilling into the soffit and stops wind from blowing through the insulation.
Common mistakes
- Skipping bays.
- Baffles too short, so deep blown insulation spills over their tops.
- Crushing the channel when stapling.
- Leaving the top plate below unsealed.
Cathedral ceilings
Vaulted ceilings need baffles that run the full length of each rafter bay from soffit to ridge, because the insulation fills the bay all the way up. Without them, those bays have no path for air at all.