Active vs. passive fire protection
Two terms that come up often in discussions of a building’s fire protection are “active” and “passive” fireproofing. Active fireproofing (AFP) measures are all of those that require some type of action in order to be effective. This action can be either triggered by ambient conditions or an individual. Examples of AFP include the activation of a sprinkler system or a person using a fire extinguisher to try to put out a small blaze. Your local fire department and the brave work they do is perhaps the finest example of AFP.
Passive fire protection (PFP), on the other hand, refers to building and landscape design elements and planned safety measures which are meant to control the spread of a fire. PFP can reduce the chance of a structure catching fire and can help to mitigate the potentially disastrous effects of a failure of AFP measures, like broken sprinklers or an extinguisher that hasn’t been inspected or replaced in a timely manner or an over-extended fire department not being able to respond to everyone in a timely fashion. Examples of PFP measures can include landscape features that reduce wildfire spread and keep flames away from the structure, roof material composition, deck or patio construction materials, fire-resistive structure vents, and fire-resistant coatings that helps to protect building materials and limit fire spread and, therefore, damage.
All PFP measures are simply design elements meant to buy time for AFP measures to take over and subdue the blaze. But that doesn’t mean they’re unimportant. On the contrary, they can make the difference between a damaged building and one that is beyond repair.
Passive Fire Protection Measures
The first PFP measure to take is to keep fire away from your building. This can be done with landscaping if you have the space surrounding your dwelling. If you don’t have the space around your dwelling, at least look to your trees and other vegetation to avoid having ladder fuels that will get a fire into the tree canopy and having trees overhanging your roof. Many websites have detailed information on fire-safe landscaping.
Quality roofing materials in good repair with proper maintenance including leaf and pine needle removal is critical to keeping a fire from starting from embers blown onto your roof.
Wildfire Rated Vents
Vents are needed in your home to allow air to circulate and allow moisture to dry. Without proper venting, areas such as crawl space under your home and your attic retain moisture and you get rot, mildew and mold.
Foundation vents allow airflow into the crawl space. Attic, soffit, dormer, ridge and gable vents allow airflow so that hot air to escape and keep the building cooler. Mesh is used to keep pests like birds, rodents, and insects out of the enclosed areas.
Most older vents were made with ¼” mesh like the image at the right. The larger the mesh, the more airflow is allowed but also the larger the ember that can enter. The ventilation Net Free Area (NFA) is the amount of space in the mesh that will allow airflow. If the mesh has been painted, the NFA can be significantly reduced.
|Mesh Size||NFA Factor|
The building code calls for a minimum of 1 square foot of NFA for each 150 square feet of crawl space. If you are upgrading older, 1/4 inch mesh, you may need to install more vents to achieve proper ventilation.
Wildfire Rated Vents provide a means through baffles or coatings to prevent embers from entering your dwelling and starting a fire.
There are two coating types of interest. An Intumescent Coating system is a combination of various compounds that, in the event of fire, “intumesce” or react together as a result of the temperature increase to form a carbon foam. When the temperature reaches about 300 degrees, this foam literally grows and attains a thickness of 10 to 100 times of the originally applied coating and insulates the substrate material through its low thermal conductivity.
Intumescents are applied in much the same way a traditional coating is applied, with very little opportunity for moisture to settle in between the coating and the substrate. Additionally, successive layers of intumescents can be applied to increase the time the coating is able to protect the substrate from extreme temperatures even further. One challenge with intumescent coatings is that they are latex based opaque coatings. There are no clear intumescents.
For clear finishes, use a Fire Retardant Wood Treatment such as “FX Lumber Guard XT” on bare wood and then topcoat with a protective water-based coating.