Ventilated attic spaces have openings in two locations. Inlet air comes from vents located in the under-eave area at the edge of the roof. Exiting air leaves through vents located on the roof or at the gable ends of your home. If your home is built over a crawl space, you will typically have vents on each face of your home to provide cross-ventilation. Experiments demonstrate that regardless of whether a vent had an inlet or outlet function, when wind blows against its face, it is an inlet vent. Therefore, any vented opening on your home should be prepared to resist the entry of embers.
Windblown embers can enter attics and crawl spaces through vents. Installing the recommended mesh screening and eliminating storage is critical to reducing building ignition during a wildfire.
For (under-eave) inlet vents, opt for a soffit eave design. IBHS research demonstrates that gable end vents and other vent openings are vulnerable to wind-blown embers when the face of the vent is perpendicular to the wind flow, while embers are less likely to pass through vents with a face that is parallel to the wind flow. Therefore, soffit-eave construction is preferred to open eave.
For outlet vents, opt for a ridge that is rated to resist wind driven rain. These vents have an eternal baffle at the vent inlet and have been approved for use by the California Office of the State Fire Marshal.
Turbine vents also help keep embers out, but you should attach a piece of 1/8-inch mesh to the bottom of the roof sheathing at the opening of the vent.