Polystyrene insulating foam board (C) Daniel FriedmanFire Protection Requirements for Foam Board Building Insulation

  • FOAM BOARD FIRE COVERING - CONTENTS: foam board insulation fire barrier requirements
    • Exposed foam board insulation in an occupied space: fire code issues
    • Drywall required to cover foam insulating board used indoors
    • Using foam insulating board for a building insulation retrofit by gluing to existing gypsum board wall surfaces
  • POST a QUESTION or READ FAQs about exposed foam board building insulation & fire safety requirements

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Exposed foam board insulation fire hazards: this Q&A article discusses the requirement for a fire-resistant covering for foam and foam-board board building insulation. Also see FOAM BOARD INSULATION TYPES, POLYSTYRENE FOAM INSULATION, and BUILDING SAFETY HAZARDS GUIDE.

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Fire Safety and Foam Insulation Board

Mineral wool insulation in an atticThe question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

What coverings are acceptable for foam insulation used indoors?


I am reinsulating a house that has concrete block walls, a stucco exterior, and 3/4-inch foil-backed gypsum board over furring strips on the building interior.

If I glued foam insulating board directly over the existing plaster wall finish, would paneling be sufficient covering? Will the foil backing on the gypsum board create a cold-side vapor barrier? - Gordon Reed Jr., Kingsford MI.

In the photograph at left, foam insulating board is shown on a garage ceiling below a second floor bedroom - this material should have been covered with fire rated drywall to meet local building code specifications for fire safety.

Answer: Fire Code Requirements for Covering Foam Insulating Board

Since most fire codes call for a minimum of half-hour fire rating over foam insulations, paneling would probably not provide a sufficient fire barrier over the foam insulating board. New 1/2-inch drywall is usually called for [and in some installations, fire-rated drywall or thicker drywall may be required for local codes and for certain applications].

The thin foil used on the back of drywall will create a moderate cold-side vapor retarder, but the exact permenance is not published for foil-backed gypsum board.

The safe tack is to use a highgraade air/vapor barrier on the inside, keeping it much less permeable than the cold side barrier. We suggest foil-faced foam insulating board with the joints sealed with foil tape.

Watch out: depending on whether or not the foil backing on the existing foil-backed gypsum board is perforated or not, the perm rating of that surface could be near zero - that is, very resistant to moisture movement, forming a moisture barrier in the "wrong place".

So it would also be a good idea to take measures to keep interior building moisture levels to a moderate level. See HUMIDITY LEVEL TARGET

solid foam insulating  board

Background on foam board insulation and fire protection:

Foam insulation board should not be left exposed in building interiors.

While many modern foam insulating products do not themselves readily support combustion (that is they don't catch fire and burn alone) they may give off thick acrid or toxic black smoke in a fire, making it difficult to safely exit the burning building.

Foam Insulation Alternatives to Solid Foam Board Insulation

Various foam insulation products that are sprayed in buildings, including UFFI, Icynene, Latex, and other insulating foams as well as fire resistant spray foam insulation used for sealing building penetrations, a different product from the foam board insulation discussed here, are described at INSULATION IDENTIFICATION GUIDE and at FOAM INSULATION IDENTIFICATION.

Original article

The link to the original Q&A article in PDF form immediately below is preceded by an expanded/updated online version of this article.

  • Q&A on Covering Indoor Foam Insulation - PDF version, use your browser's back button to return to this page. Original article, Solar Age Magazine, September 1985, adapted and updated for InspectAPedia.com November 2010.

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