Use of rigid foam insulation on the building interior  (C) Daniel Friedman Indoor Use of Foil Faced Polyisocyanurate Foam Insulation: Hazards?

  • POLYISOCYANURATE FOAM INSULATION - CONTENTS: Are there any health hazards associated with applying rigid foil-faced insulating foam (polyisocyanurate insulation) on the interior side of walls?
    • Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
  • POST a QUESTION or READ FAQs about using polyisocyanurate foam insulation in buildings

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This article discusses the question: are there any health hazards associated with applying rigid foil-faced insulating foam (polyisocyanurate insulation) on the interior side of walls? Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

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Indoor use of foil faced polyisocyanurate foam insulating board

Celotex polyisocyanurate insulation board (C) Daniel Friedman

The question-and-answer article about the indoor use of foil faced insulating foam found just board below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Is Foil Faced Polyisocyanurate Foam Insulation Hazardous when Used Indoors?

Are there any health hazards associated with applying rigid foil-faced polyisocyanurate insulation on the inside of the existing walls of a living space?

I am aware that these insulations give off toxic gases as they burn. The question in my mind is whether they are safe on a day-to-day basis within the building envelope with an air change rate of say 0.75 ACH per hour? -- R.H. Mendocino CA

Our photograph (above left) shows Celotex Super Tuff-R polyisocyanurate insulating board used indoors.


Rigid polyisocyanurate insulation is foamed from freon gas, a fluorinated hydrocarbon often used as a refrigerant and until the early 1980's, as a propellant in aerosols. [Currently non HFC gases are used for foam insulation production --DF] The earlier-used Freon gas family and modern refrigerants are inert gases and are considered non-toxic, except in very high concentrations of over 1000 ppm [at which point even an inert gas can cause asphyxiation].

The small quantities of gas that will be released from this foam insulating board [until it has "cured" and stopped outgassing] by diffusion or rupture are not considered a health hazard by the several health authorities we contacted. The upper-limit service temperature for this type of foam is 250 degF.

In uncontrolled combustion, all flammable building materials release high levels of toxic fumes. The National Fire Protection Association (NFPA) recommends that all insulation products be contained behind drywall or a suitable fire retarder. A check with your local building officials is almost certainly going to confirm that foam insulation products may not be left exposed in the living area.

In our sketch at page top you will see that the solid foam insulating board in that illustration is placed on the building interior wall surface, but it has been covered with furring strips and then drywall. The furring strips provide a dead air space, increasing the wall's R-value, and the space is in some conditions also used for routing wiring.

The hazard with foam insulation products is of production of toxic fumes or smoke release during a building fire, not outgassing during normal building conditions.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Reader Question: using polyisocyanurate form insulation in the roof (ceiling) of our out door sauna

(Aug 6, 2011) Diane said: Hello great article. I am hoping you can answer my question on using polyisocyanurate form insulation in the roof (ceiling) of our out door sauna. We are planing to use them in ceiling then cover them with foil as a bearier then apply the tonge and grove cedar to the ceiling. Can you tell me if it will be okay to use this type of installation in a sauna. My concern is the heat generated by the sauna and off gasing. Please let me know if it is safe to use this product. Thanks for your assistance.

(Aug 7, 2011) Diane said: Thanks DanJoeFridman for your opinion and information. I will send this web site to our builder to review. And we will be installing a metal roof for the sauna. But I am still unsure about the off gasing of this product. Do you know anything about that aspect of this product?

Reply: Air leaks as a moisture source in roofs versus need for a vapor barrier

DanJoeFriedman (mod) said:

Diane my OPINION is that the installation of a foil vapor barrier forms a perfect vapor barrier - foil has a perm rating close to zero - except if it's cut or penetrated. (It's probably fine for the ceiling covering nails to penetrate the foil where it crosses over ceiling joists).

There are fire code and fire barrier standards that make sense to apply to any occupied building, not just your home, but also outbuildings like a sauna. Check with your building department to ask if the fire barrier formed by the T&G cedar ceiling is adequate to meet the code requirement for covering foam insulation. If it's not, you can add a layer of fire-rated drywall before installing the ceiling boards.

Finally, while I like the energy efficiency of foam insulation installations, I'd take extra care to inspect and maintain the building roof - from outside. A foam-insulated ceiling without ventilation and without inspection access (say a foamed cathedral ceiling) can't be inspected for leaks from inside. Any damage to the roof that causes a leak can result in very extensive damage to the insulated ceiling before you'd notice it indoors.

On a recent foam-insulated ceiling project we opted for a standing seam metal roof for these reasons.


Continue reading at POLYISOCYANURATE FOAM BELOW SLABS or select a topic from the More Reading links shown below.



Readers should also see FLOOR, CONCRETE SLAB CHOICES for a discussion of choice of finish floor materials to preserve use of thermal mass of a concrete floor slab.

Readers interested in basement insulation improvements should also see INSULATION LOCATION for BASEMENT WALLS and BASEMENT HEAT LOSS.

For more general energy savings advice see ENERGY SAVINGS PRIORITIES, and our insulation home page at INSULATION INSPECTION & IMPROVEMENT.

If you are going to insulate under a basement or grade-level concrete slab floor, be sure to read SLAB INSULATION, PASSIVE SOLAR.

Finally, readers considering adding insulation inside or outside a basement foundation wall should see POLYSTYRENE FOAM INSULATION as well as BUCKLED FOUNDATIONS due to INSULATION? Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Suggested citation for this web page

POLYISOCYANURATE FOAM INSULATION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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