Pressure Impregnated Treated Products

Both Premium and Number One Grade products are available with pressure impregnated fire retardant or preservative treatment. Both treatments are not available in the same product. This type of treatment is not a topical spray-on and will not leach out after a rainstorm. Pressure impregnated treated products are identified by the treatment label attached to the bundle strapping.

Architect: Gary Tabasinske, AIA Photo: Chris Eden

Pressure Impregnated Fire Retardant Treated
Cedar Shakes and Shingles

In areas prone to wildfires, pressure impregnated fire retardant treated cedar shakes and shingles are a wise choice. Through pressure injection at the factory, a special fire retardant treatment is forced into the cells of the wood. Kiln drying solidifies the formula and locks in the fire protection. For roofs, there are Class A, Class B, Class C, and unrated roofing systems. Cedar shake and shingle roofs exist in all these classifications. These classes are the same for all roofing materials, including asphalt, metal and concrete tile.

• Class A is appropriate for institutional applications, such as hospitals and correctional facilities. This classification uses a Class B fire retardant treated product along with a rated fire retardant fiberglass cap sheet underlay. A Class A roofing system is effective against severe fire exposures. Under such exposures, roof coverings are:
  
  
  • Not readily flammable
  
  
  • Afford a fairly high degree of fire protection to the roof deck
  
  
  • Do not slip from position
  
  
  • Pose no flying brand hazard
  
  
• Class B is often used in apartment buildings, condominiums, commercial buildings, and dwellings in wildland interface areas. Class B fire retardant treatment is effective against moderate fire exposures. Under such exposures, roof coverings of this class are not readily flammable, afford a moderate degree of fire protection to the roof deck, do not slip from position and pose no flying-brand hazard.


• Class C is typically used for single-family residences and duplexes, where fire retardant roofing is desired. This is a product that is effective against light fire exposures. Under such exposures, roof coverings of this class are not readily flammable, afford a measurable degree of fire protection to the roof deck, do not slip from position and pose no flying-brand hazard.

U.S. building codes require that fire retardant treated wood roofing products are subjected to rigorous fire retardancy tests. The Spread of Flame test is performed to measure the spread of flame over a deck and the Intermittent Flame, Burning Brand and Flying Brand tests are completed before and after both accelerated weathering and long term weathering of one, two, three, five, and ten years.

Wildfire mitigation should include residential fire prevention strategies for building design, construction materials, and plant selection. Vegetation management practices, including sensible landscape choices, brush setbacks, firebreaks and forest debris clearing, are critical to preventing and minimizing firestorm damage. Local building officials have specific information regarding jurisdictional regulations and these should be included in project specifications.