styrofoam for home insulating

Is sheet and blown-in styrofoam considered safe for home insulating?

It must be covered

Burning Styrofoam, or polystyrene, is the least appropriate way to get rid of it for both people and the environment. Research has shown that when Styrofoam is burned it releases toxic chemicals and smoke that can damage the nervous system and lungs. These chemicals need to be ingested in large amounts or over a period of time to show significant damage, so burning a small amount of Styrofoam accidentally won’t harm you or the environment significantly. When Styrofoam is safely burned as a method to dispose if it, it is burned in a controlled environment at extremely high temperatures. Campfire or trash burning temperatures will not burn hot enough to keep toxic chemicals from forming and toxins to be released.

Read more: What Are the Dangers of Accidentally Burning Styrofoam? |

I don’t think Styrofoam would pass the required tests for flame spread. Covering the material would not make it acceptable.

R302.10.1 Insulation. Insulation materials, including facings,
such as vapor retarders and vapor-permeable membranes
installed within floor-ceiling assemblies, roof-ceiling assemblies,
wall assemblies, crawl spaces and attics shall have a flame
spread index not to exceed 25 with an accompanying
smoke-developed index not to exceed 450 when tested in accordance
with ASTM E 84 or UL 723.


  1. When such materials are installed in concealed
    spaces, the flame spread index and smoke-developed
    index limitations do not apply to the facings, provided
    that the facing is installed in substantial contact with
    the unexposed surface of the ceiling, floor or wall finish.
  2. Cellulose loose-fill insulation, which is not spray
    applied, complying with the requirements of Section
    R302.10.3, shall only be required to meet the
    smoke-developed index of not more than 450.

Code Commentary:
Section R302.10.1 addresses the various insulating
materials that may be installed in building spaces, including
insulating batts, blankets, fills (including vapor
barriers and vapor-permeable membranes) and other
coverings. Exposed insulating materials represent the
same fire exposure hazard as any other exposed material,
such as an interior finish. The provisions of Sections
R302.10.2, R302.10.3 and R302.10.4, as well as
the foam plastic provisions of Section R316, should
also be reviewed based on the actual type of insulation
and how it is installed. As a general requirement, insulation,
including facings used as vapor retarders or as
breather papers, must have a flame spread index not
in excess of 25 and a smoke-developed index not in
excess of 450. These values limit the contribution of
the insulation to a fire. The flame spread requirement
of 25 for the insulation will be more limiting than the
200, which is accepted for interior finishes by Section
R302.9. The test method used to establish these limits
is either ASTM E 84 or UL 723. See the commentary to
Section R302.9.3 for additional information.
The two exceptions address situations where, because
of the way the material is installed or because of
other imposed regulations, the material does not make
any significant contribution to a fire. The first exception
eliminates the flame spread and smoke-developed indexes
for the facing portion of the insulation if it is installed
“in substantial contact” with the unexposed sur-
face of the ceiling, floor or wall finish. For example,
when paper-backed insulation is placed directly on top
of a ceiling, the paper facing is not required to meet the
smoke and flame spread limits. If the same material is
applied to the underside of a roof deck and the paper
facing is exposed to the attic space, the paper facing
must then meet the general criteria. The potential for
flame spread is greatly diminished when the facings
are installed in direct contact with the finish material
because of the lack of airspace to support a fire if the
facing were to be exposed to a source of ignition. See
Commentary Figure R302.10.1 for an example of the
various facing provisions.
The second exception addresses the fact that cellulose
loose-fill insulation is federally regulated by the
Consumer Product Safety Commission (CPSC). Parts
1209 and 1404 of CPSC 16 CFR contain various requirements
that regulate the product to avoid excessive
flammability or significant fire hazards. The
smoke-developed index for cellulose loose-fill insulation
must be determined by either the ASTM E 84 or
UL 723 test and must be 450 or less. This section requires
that the smoke-developed index be measured
using the either the ASTM E 84 or UL 723 test rather
than the test procedures specified in Sections
R302.10.2 and R302.10.3.

R302.10.4 Exposed attic insulation. All exposed insulation
materials installed on attic floors shall have a critical radiant
flux not less than 0.12 watt per square centimeter.

Code Commentary:
This section provides the performance requirements
for the test exposure that insulation must meet when it
is exposed on the floor of an attic. It is tied to the testing
provisions found in Section R302.10.5, which specifies
that the ASTM E 970 test is to be used for determining
the critical radiant flux. See the commentary to
Section R302.10.5 regarding the application of this requirement
to cellulose loose-fill insulation.

R302.10.5 Testing. Tests for critical radiant flux shall be made
in accordance with ASTM E 970.