Is Attic Insulation Fireproof?

Most types of attic insulation are rated fireproof or fire resistant. Building codes require insulation to meet high fire standards. Insulation causes less than 0.5% of house fires but some of them can be a fire accelerator.

Is Attic Insulation Fireproof?

Fireproof Or Fire Resistant Insulation?

The terms fireproof insulation and fire resistant insulation are often used interchangeably. They are not the same. Most insulations are naturally fire resistant or have additives–like borax–to enhance fire resistance.

Fire resistant is probably the more accurate term to describe insulation properties. Almost anything will burn, melt, or become deformed if it gets hot enough–including rock. House fires can reach 1500 degrees F. at the ceiling. Add an accelerant such as natural gas, heating oil, or propane, and the fire will be much hotter. (Propane fires can reach 3500 degrees F.)

Common Types of Attic Insulation

All types of attic insulations resist fire and restrict flame spread to varying degrees. They still must be installed properly to prevent fires. Away from heat sources such as pot lights and chimneys. Faulty electrical wiring is one of the leading causes of attic fires. Smoldering insulation can cause enough heat for surrounding framing members to ignite.

  • Cellulose Loose Fill Insulation – Cellulose insulation is recycled paper treated with the fire retardants boric acid and ammonium sulfate. It is very dense without the air pockets of fiberglass. Cellulose smolders but rarely bursts into flames. The following video shows the difference between burning houses with fiberglass insulation and cellulose insulation. The cellulose-insulated house lasts much longer.
  • Fiberglass Loose Fill and Batt Insulation – Fiberglass insulation–loose fill or batts–does not burn–making it fireproof. It is rated to melt at over 1000 degrees F. Melted fiberglass releases oxygen trapped in the fibers to feed the flames. Kraft paper-backed fiberglass is a hazard if a fire starts because it contains petroleum products that will burn. Paper-backed is rarely used in attics.
  • Mineral Wool Loose Fill and Batt Insulation – Mineral wool insulation is naturally non-combustible. It is made of rock and iron slag and is denser than fiberglass without the amount of air pockets. Mineral wool insulation melts at 2150 degrees F but does not catch fire. It also slows flame spread.

Less Common Types of Attic Insulation

  • Spray Foam Insulation. Spray foam insulation is flammable but has a Class 1 fire rating. Meaning that it will not catch fire for an hour. It helps prevent flame spread.
  • Rigid Foam Board Insulation. Most building codes require rigid foam board insulation to be covered by material with a minimum half-hour fire rating because of its low ignition point of 700 degrees F.
  • Reflective Insulation. It does not burn but reflective insulation does melt. It does not support flame spread.
  • Vermiculite Insulation. Vermiculite insulation does not burn and does not promote flame spread. Used in older homes, it is often contaminated with asbestos.
  • Asbestos Insulation. Until 1980 asbestos insulation was used throughout North America. One of the attractions of asbestos is that it is completely fireproof.