Vents

IBHS Attic and Basement Vents and Wildfire Fact Sheet (1MB PDF)

Vents on homes create openings for flying embers.  Ember entry through vents can result in ignition of combustible materials in the attic, and result in a building burning from the inside out.  The importance of ember and flame entry into vents during wildfires has resulted in the development of commercially available vents designed to resist the intrusion of embers and flame, and recomendations for new or retrofit vents to protect existing openings.  Ember resistant vents are adrressed in Chapter 7A of the California Building Code.

• Cover all vent openings with 1/8-inch or 1/16-inch wire mesh.   
• Common 1/4" screens are ineffective, and should be replaced. 
• Do not use fiberglass or plastic mesh because they can melt and burn.
• Protect vents in eaves or cornices with baffles to block embers, backed by 1/16" wire mesh (mesh alone is not enough).

If enough embers are able to enter the building through a vent or open window, they can ignite materials inside the building. An ember that gets inside an attic or crawl space could ignite items stored in those locations, such as newspapers, cardboard boxes, or insulation. 

VENTS & EMBER RESEARCH

Read the report "Vulnerability of Vents to Wind-Blown Embers" to learn about recent research conducted to evaluate vents for wildfire ember resistance - https://disastersafety.org/ibhs/wildfire-vulnerability-vents-wind-blown-embers/.  This reports adds to a growing body of literature on how buildings can be ignited by wind-blown embers by focusing on the vulnerability of vents to embers. 

Quarles, Stephen L.  2017.  Vulnerability of Vents to Wind-Blown Embers.  IBHS. 

SUMMARY OF FINDINGS

1. There are two options for inlet vents, both located in the under-eave area. These include vents in the between-rafter blocking in open-eave construction and vents in the soffit material in soffited-eave construction. Vents located in soffited-eave construction were shown to limit ember entry and should therefore be the preferred construction type.
2.  ¼-in. (6 mm) mesh screening should not be used to cover any vent.  Finer mesh sizes of ⅛-in. (3 mm) or 1/16-in. (1.5 mm) are preferred. The finer 1/16-in. mesh screen requires more cleaning-related maintenance to remove the debris that can accumulate on the screen surface.
3. The wildfire-resistant vents used in the gable end location performed better than the respective backing screen mesh alone.
4. Due to the relatively large size and vertical orientation of gable end vents, they should be avoided. If alternatives are not possible, a wildfire-resistant gable vent that has passed ASTM E2886 should be used.
5. Avoid using non-wildfire-resistant off-ridge and ridge vents. Of the ridge and offridge outlet vent options, the following performed well:
   1.  Miami-Dade wind-driven-rain-compliant ridge vent
   2. Wildfire-resistant off-ridge vent
   3. Turbine (off-ridge) vent
6. Wind-blown vegetative debris must be removed from the inlet of all ridge and off-ridge vents, paying particular attention to vents with plastic components. Plastic components are commonly used in ridge vents.