Fire hazard - Vents
Originally, vent screens were intended to keep rodents and small animals out of attics and crawlspaces. However, depending on the mesh size and type of screen, small materials may pass through the grid and deposit in enclosures. During a fire, small embers can also penetrate the vents and ignite fine combustibles. Woody structures and other flammable materials may be ignited as well, with catastrophic consequences for the entire building.
Detailed technical information can be found here.
How can you protect your vents?
The first step is to locate all vents on your property (attic, crawl space, laundry room, etc.). After that, determine whether they need immediate attention:
- Is the mesh screen larger or equal to 1/4” (6.4 mm)? Large embers would be able to easily pass through them. Consider using smaller mesh screens (1/8” or smaller).
- Are the vents made of combustible materials (like plastic)? In contact with flames or embers, they would burn and fully expose the house interior to embers and flames. Consider replacing the vents, or retrofitting them.
- Is there any vegetation or combustible material within 5ft (1.5m) from the vents? They may generate flames and embers that would directly impinge on vents when burning.
- Does the mesh screen have debris and/or paint clogging it? As a result, they would not be effective in removing moisture, and debris may burn if they come in contact with a flame. Check your vent screens regularly.
Traditional vents should be changed or retrofitted to improve their fire resistance. Vents should be checked regularly, and vegetation and combustible materials should be kept away from their surroundings.
If you cannot replace or improve your vents, prepare temporary plywood vent covers to install before a fire approaches, or use metal tape to temporarily seal the vents.
According to Chapter 7A, screen mesh for roof vents should be made with corrosion-resistant and non-combustible materials, with openings between 1/16 and 1/8" (1.6 and 3.2 mm). In addition, Chapter 7A prohibits the use of vents in eaves unless they have proven to resist the intrusion of embers and flames.
Products and assemblies that have complied with Chapter 7A can be found in the WUI Product Handbook. Since “ignition resistant” and “non-combustible” are performance-based characteristics (i.e., there is a standard test to show compliance), these materials are included in the Handbook.
Here are a few examples of fire-resistant vents. We will try to update this list on a regular basis.
|Vulcan vents. They use screenings on the front and back of a honeycomb matrix. This matrix is coated with an intumescent paint that swells when contacted by flames.|
Brandguard vents. These vents use a baffle design to deviate the embers path.
Embers out. These vents have multiple internal layers of louvers that block embers.
O’Hagin’s vents. Low profile through-roof vents, approved for over eave applications.
Examples of traditional vents
|Soffit vents. The vent shown in this picture is located in the under-eave and has a ¼” mesh screen. This mesh would allow embers to reach the attic.|
|Gable vents. This common type of vent serves both as an intake and exhaust vent and it’s installed on opposed sides for cross-ventilation. Embers could easily pass through this vent exposing the attic to potential ignition.|
|Vent clogged by paint. Embers passing through 1/4'' mesh screen have sufficient energy to ignite fine fuels. Finer mesh screens would reduce the risk of ignition (smaller embers would have less energy). However, they may become clogged with debris or paint, negatively impacting the moisture management function of vents.|
|Siding vent. Vents like this can be found on the exterior walls of a house. This large mesh screen could allow embers to enter the house.|