The dictionary defines flammable as “capable of being easily ignited and burning quickly,” and cellulose insulation does not fit that definition. But it is “combusible,” which means capable of being ignited. Cellulose smolders slowly when it starts to burn and, if installed too close to an ignition source like a gas flue or recessed light fixture, will eventually ignite and can spread to start a larger fire in nearby materials that are more flammable. 

    Because improper installation is a key factor, the Consumer Products Safety Commission (CPSC) requires that consumers be warned of the potential problem at time of purchase of the material. Here’s what the CPSC says, in the Code of Federal Regulations at 16 CFR Ch.II Part 1404 - Cellulose Insulation: 

"Based on available fire incident information, engineering analysis of the probable fire scenarios, and laboratory tests, the Consumer Product Safety Commission has determined that fires can occur where cellulose insulation is improperly installed too close to the sides or over the top of recessed electrical light fixtures, or installed too close to the exhaust flues from heat producing devices or apparatus such as furnaces, water heaters, and space heaters. These fires may result in serious injuries or deaths. Presently available information indicates that fires may occur where cellulose insulation is improperly installed even though the cellulose insulation complies with the Commission’s amended interim standard for cellulose insulation (16 CFRpart 1209) based on GSA SpecificationHH-I-515D. The Commission has determined that it is necessary to require labeling to inform persons installing cellulose insulation and consumers in whose homes the insulation is installed of the fire hazard associated with improperly installed cellulose insulation and the method of properly installing the insulation to prevent this hazard."

    The underlined part of the text above is significant, because it notes that even cellulose that meets the CPSC standard for treatment with fire resistant chemicals is combustible if installed improperly. 

    However cellulose insulation also has a number of virtues to consider when comparing it with other insulation products. It is a “green” building material that is about 85% recycled newpaper, gives off no volatile gasses when installed (like the spray foram insulation shown below), and can be effective sound insulator.

    Also, see our blog post Why is insulation not allowed to touch around a gas flue in the attic even if it’s not flammable?

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Here’s links to a collection of our blog posts about INSULATION: 

• What are the common problems with attic insulation?

• Why is vermiculite attic insulation a problem for both buyers and sellers of a home? 

• Why is the garage so hot in the summer?

• How can I tell if a house has insulation?

• Why is spray foam used for attic insulation?

• Should I wrap the water heater with an insulation blanket? 

• Should I put some more insulation in the attic?

• What does the "R-Value" of home insulation mean? 

• Is pipe insulation flammable?

   Visit our INSULATION page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.