Fire Resistant Roofs and Their Rating System

An ideal roof covering is one that is difficult to ignite.  With the large number of forest fires in the U. S. every year homeowners and insurance companies are looking more closely at roofing systems that are less combustible.

The national fire protection association has a standard method for testing roofing assemblies for their heat release rate and susceptibility to combustion.  These standards classified roofing system as a class A, class B, class C .  This is based on their ability to:

  • Resist flames spread on the roofing system
  • Resist the spread of fire into the attic
  • Resist burning embers and their generation

Class A roofing systems:

metal roofing system installationA class A roofing system is non combustible such as metal, tile and slate.  A class B roofing system is treated with a fire retardant chemical for example treated wood shingles.  An example of a roof covering system that is categorized as unrated would be untreated wood shingles.  Now a class B roofing system can be classified as a Class A roofing system if it is installed with additional fire resistant elements in the assembly.  You’ll find these four classes of roof covering on buildings throughout your city.

A pitched roof can use any one of a variety of roofing systems, to include:

  • Wooden shingles that are treated during manufacturing with fire resistant chemicals.  Although, over time and weather wear these chemicals can be less effective.
  • Asphalt shingles and rolled roofing are made from live natural fiber which is combustible.  A sand like material is applied to give the shingle color and it is less ignitable.
  • Type I shingles are made from Terra Cotta or concrete and are not combustible although this type of tile roofing can become slippery when wet and more dangerous to walk on.
  • Slate shingles are a non combustible natural stone and are installed in thin layers when used for roofing.  Similar to tile roofing systems they are slipperiest when wet and hazardous to walk on.  In humid areas they can grow moss and mold which requires additional maintenance for upkeep.
  • Metal roofing systems are sheets of metal that are cut to various widths and sizes depending on the project and are non combustible.  These to our slippery when wet and should not be walked on when wet.


Wood and asphalt shingles are easy to cut and modify, which makes them easy to work with around vents and chimneys.  Slate tiles are difficult to cut, making them more difficult to work with.  Additionally, slate and title roofing systems are heavier and require additional support for hold up the added weight.

Modern roofing materials are made to look similar to the traditional materials discussed above.  For example, plastic panels are colored, formed and shaped to look like wood shingles, tile shingles were even slate shingles.

The fire rating on your roof is based on the type of roofing material, sheathing and roof supports such as rafters and trusses is used in the assembly of your roof.  All of these together will classify your roof and can affect the cost of your insurance.

To learn more about the best roofing system for your individual needs, contact Associated Roofing of Tennessee and request your free no obligation quote and inspection.


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