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Don’t Ask …. Don’t Tell

homedesign | Posted in Building Code Questions on

I recently read a TROUBLESOME comment by Li Ling Young in Martin’s “OK to Skimp” blog:

Li Ling (on 2/6/10) brought up an important CODE Safety question….
Is it possible that the building code may NOT allow uncovered spray foam installations beyond 5 or 6 inches thick?
Is this true?
How can this be true?
If this IS true… how can the practice of spray foam rafter encapsulation be so wide spread?

Many Building America Projects include open cell spray foam installed in attics with foam thickness well beyond 5 inches.

The GBA website is chock full of examples.(including one of my projects)
Almost every Green home tour I have visited in Texas has attic rafters covered in spray foam.
My thinking WAS that this practice is acceptable,safe and code approved.

I am currently a Confused Architect…….

Martin Holladay offered his opinion here:(2/18/10)

My Question seems to be a Hot Potato.
I feel like the student who reminded the teacher that she forgot to assign homework.

I would like to hear an opinion or comments from other Members and Advisors
and especially the resident GBA Code Official – Lynn Underwood

Let me ask it this way…..
Is it possible to encapsulate 2×6 roof rafters with unprotected open cell spray foam and still satisfy the current building code?
Please begin your answer with a YES or a NO

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    Yes it is possible to safely install spray foam to completely encapsulate the framing members.

    However, the "flame tunnel test" mandated by the code for flame spread cannot accommodate testing of material thicknesses greater than 5"

    So alternative test methods have to be used to prove safety of foam at thicker than 5" which has been done.

    But the fire retardants used in foam may have Endocrine Disruption potential.

    However the foam industry lists Flame Retardant as "trade secret" on their MSDS sheets so we don't really know.

    Intumescent ignition barriers are not much use if the ceiling joists are on fire and are washing the bottom side of the foam with fire releasing smoke that is poisonous to the firemen.

    However a sealed attic has no way for air to enter and exit and is therefore much less prone to fire than a ventilated attic due to oxygen limitation.

    My opinion of best practice:
    - Any access to the attic for storage or equipment should be separated from the foam by a layer of sheetrock to keep air and ignition hazard away from the foam.
    - Avoid shaving the foam as when installing in walls to keep the dust from getting loose in the house
    - Out gassing appears to be not a problem after three days from installation.
    - Don't circulate air from the house in the same space as un-protected spray foam.
    Sealed attics and crawls with foam should not have conditioned air circulating in them and back into the house. Dead air is best in attics.
    Okay to pull air from the house through the crawl and out as part of an exhaust-only ventilation system.

    Robert Riversong will sign on momentarily and take issue with all of the above.


    Just to be clear, the alternative test methods are subject to approval on a case by case basis by the inspections department.

    And I like it that Robert constantly disagrees with me. There are a lot of different ways to do things which is why we have this place for conversations. I feel good about the way I build homes and run my business as does Robert and we do many things very differently, work with very different clientele, live in different climates and value the cost of labor very differently.

    Sometimes I do feel misunderstood and quoted out of context by him but I don't think it is all that productive to debate every issue there. Better to just express our different points of view and let the readers sort it all out. This disagreement is what makes this conversation so interesting. So Robert, please do continue to call my thoughts "absurd" and thank you for bringing your perspective to the conversation.

  3. GBA Editor
    Martin Holladay | | #3

    You and I may agree that intumescent coatings aren't much use in this application, but, considering Icynene's evaluation report —
    — I don't see how a building code official could accept the installation you describe without the required ShelterShield intumescent coating.

  4. Riversong | | #4


    Thanks for the back-handed invitation. I'll take you up on it. First, as a long-time volunteer firefighter, I have to say that a tightly-sealed, highly insulated, non-combustible attic can be a liability in a fire. One of the first things we do at a structure fire is break upstairs windows or cut holes in the roof (if the fire is in the attic) to ventilate the fire. That doesn't mean to give it combustion air, but to give the superheated air an escape route. Otherwise the entire building becomes either an inferno (if it has sufficient oxygen) or a bomb waiting to explode (if it is superheated but smoldering).

    The issue about toxic smoke from plastics is a red herring, since wood smoke contains 200 toxic chemicals in the inhalation range, will quickly overcome a sleeping occupant, and firefighters have been required for a long time to use self-contained breathing apparatus (SCBA) in or near structure fires.

    As to the issue of code compliance, there is a new ICC-ES testing protocol for sprayed foams that went into effect Jan 1, 2010, requiring flame spread consistent with the code-approved 1/4" plywood ignition barrier. Some spray foams have passed this test with intumescent coatings and at last a couple have passed with no covering.

    And there is at least one "green" latex paintable coating that is approved as both a thermal and ignition barrier:



    I don't follow your concern.

    Icynenes literature seems to recommend using the coating when the attic is accessible for storage or equipment. I am recommending creating a small storage room enclosed with 1/2" sheetrock to separate attic areas used for storage or equipment from attic areas insulated with spray foam that are not covered with the coating.

    This assures that that there are no areas used for storage or equipment that are not also separated from the foam with a layer of sheetrock and therefore no need to use the coating. a 12x12 storage area w/ sheetrock is, in my experience, easier to implement and less expensive than the intumescent coating. Plus it further separates the foam from the living space.

  6. GBA Editor
    Martin Holladay | | #6

    Let's just put it this way: the Icynene ESR is written in such a way that it appears to me that an intumescent coating is required when the Icynene is not covered with drywall. However, the writing of the ESR is far from clear. I wish all writers of technical documents were English majors instead of engineering majors — then they might be able to craft English sentences free of ambiguity.

    Of course you're right that all this ambiguity lands in the lap of the local code enforcement agency, who makes the final ruling.

  7. GBA Editor
    Martin Holladay | | #7

    In a posting addressed to me, Paul Duffy has answered the question here:

    Paul wrote,
    "Hello Martin,
    Sorry I have not checked into this discussion for a while. ...You and others appear to have captured most of the key points…"


    Martin, the ambiguity as I see it is in the definition of "covered in drywall" our inspectors are interpreting it as having drywall separating the foam from the home at the ceiling and band joists etc. Your interpretation seems to be that the drywall (or intumescent coating) should be in contact with the interior surface of the foam up against the bottom of the rafters and between the joists at the rim. I see your point but hadn't interpreted it that way myself. if that is the correct interpretation then, yes, you would have to cover all foam with intumescent coating and further increase the cost of this strategy.

    I think we agree (along with our local inspectors) that the intumescent coating is of very limited value in a house fire given that most fires are going to originate in the conditioned area and will be pretty well developed by the time they break through the drywall ceiling plane and involve the spray foam.

  9. Expert Member
    ARMANDO COBO | | #9

    I've asked the same question to many code officials and not found a direct code answer to the same question except for whether you use the prescriptive or performance code; and outside the code, it is so unfurtunate that must all answers are DEPENDS!!!. It DEPENDS on which green scientist or GBA advisor you subscribe to; must of them do not agree with each other on some issues and in most cases there are convincing arguments on both sides.... etc.
    Until the code addresses this issue specifically, my rules are:
    1. If my client uses the prescriptive code, I use R38+ in CZ3-4 & R49+ in CZ4-5.
    2. If my client uses the performance code, I use Foam under decking R20 in CZ3 but highly recommend 1/2" rigid insuation in CZ3 above decking, use 1" rigid insulation in CZ4 and use 2" rigid insulation in CZ5 to avoid condensation issues (I really do like this application).
    3. If the foam insulation is covered by 5/8" sheetrock, it has the 1hr fire rating. If the foam is not cover, I use intumescent coatings.

  10. homedesign | | #10

    It has been almost a year since I posted this question in the BUILDING CODE section.
    I did get some comments and opinions.....BUT

    I never did get an answer from GBA's Building Code ADVISOR....
    Lynn Underwood

    Is there any new "news" about this issue?

  11. homedesign | | #11

    If an Intumescent coating and/or Drywall Covering IS used.......
    What is the Maximum thickness that Open Cell Foam can be legally applied?

  12. GBA Editor
    Martin Holladay | | #12

    The manufacturer or supplier of your spray foam product should be able to answer your question. Ask to see the ICC-ES (ICC Evaluation Service) report on the product you intend to use.

    The last time I reported on this issue (for the April 2008 issue of Energy Design Update), I quoted from a public letter written by John Hogan, the senior code development analyst for the Seattle Department of Planning and Development. In his January 23, 2007 letter to the ICC-ES Evaluation Committee, Hogan noted: “The ICC-ES reports specify maximum thicknesses for the products ranging from:
    6 inches maximum in ESR-1383 (BioBased 501),
    2 inches maximum in ESR-1615 (Insulstar),
    6 inches maximum in ESR-1172 (Sealection 500), but only 3.5 inches maximum for attic walls,
    5.5 inches maximum in NER-420 (Icynene), but 6 inches in certain attic constructions,
    2 inches maximum in ER-3974 (Froth-Pak).“

    It's possible that the manufacturers of these products have conducted more testing since 2008, and that further testing has allowed the manufacturers to increase the maximum installed thickness limits for their products -- so check with the manufacturers for up-to-date information.

  13. Daniel Morrison | | #13

    Sorry, John. Bickering and rude posters chased Lynn away quite some time ago. One of the first casualties, and a warning sign I should have paid closer attention to a long time ago.

    If anyone out there knows a building official who enjoys the nuances of building science, please send them to this thread.

  14. 2tePuaao2B | | #14

    If these recommendations are being made on this site the safety and code information should be readily available as well.
    Regarding site bickering... proper site management requiring the use of real names would minimize silly bickering. Heated discussion pertaining to differances of opinion regarding green building technique are normal and most times produce reasonable compromise. Until it gets personal. I'm really glad that Robert wasn't chased away.

  15. MICHAEL CHANDLER | | #15

    John, it's my understanding that the flame tunnel test referenced in the code doesn't permit testing of foam at more than six inches and that a new testing protocol is required in order to test foam at greater thicknesses. So until that test is adopted it is technically illegal to install spray foam at greater than six inches. I advocate spraying eleven inches and certainly never less than eight here in North Carolina so technically all of my homes are in violation of code on this issue.

    Armondo made a similar point about the definition of "conditioned" as it applies to attics and crawls that he interprets it as requiring circulation of conditioned air through these spaces, which would of course expose them to humidity from the living space and air in the case of fire. My interpretation is that the closed attics and crawls should be inside the insulation envelope but don't need to and shouldn't have conditioned air circulating through them to add humidity or bring in air in case of fire.

  16. Danny Kelly | | #16

    John - I think the answer is yes, kind of, maybe. I have asked our code officials several times about proper thickness, flame spread, when does it need a retardant, sheetrock, not meeting required R-Value, etc. They basically told me it all comes down to the ICC evaluation report. I recently had a customer request foaming his roof - I warned him of the potential issues and gave him links to several conversations on this site. He ultimately decided to go ahead with the spray foam but I did convince him to install 8" in lieu of 5". We had 2x6 roof rafters so they were completely covered with foam. I got the ICC reports from the installer/Icynene to have on hand for the building inspector. Inspector came and passed everything and never asked for the reports. So I am still confused but I think they are just ignoring the questions at this point.

  17. 2tePuaao2B | | #17

    No.Have you guys read the latest posts regarding attic fume problems associated with foam use in these area's?

  18. 2tePuaao2B | | #18

    Why would such an important question be ignored Danny?

  19. user-958947 | | #19

    I'm not understanding a very basic point. Is the allowable foam thickness issue just a matter of the code testing apparatus not being able to accommodate the thickness? Or is there another issue? What is the science behind thinner is OK, but thicker isn't? Is it just a matter of the volume of combustible material?

  20. GBA Editor
    Martin Holladay | | #20

    There is evidence that thicker foam is more of a fire hazard than thin foam. The code requires foam manufacturers to test their foam for fire safety. The fire safety question -- and the question of which test methods are appropriate -- are matters of enormous controversy and uncertainty, even among code officials and foam manufacturers.

    If a foam manufacturer can't come up with an ICC-ES evaluation report that refers to an assembly with foam thickness equal to or greater than the one you are planning to install, it's certainly possible that a local code official can refuse to allow the installation.

  21. user-958947 | | #21

    My interest is with an unvented attic. I'm using Sealection 500. I asked Demilec for info, and they directed me to ESR-1172 updated 2-1-11.
    Section 4.4 addresses attics------ It appears that you can use up to 11 1/2" under the roof, and up to 9 1/2" on vertical surfaces. The foam must be sprayed with an intumescent coating (both under the roof and vertical surfaces), or covered with an ignition barrier (like plywood), or a thermal barrier (like drywall).
    Note that the old ESR allowed 11 1/2" and 10" thicknesses, but required IC's only on the vertical surface. So, I'm assuming that a house permitted last year would legally require IC only on the uncovered vertical foamed surfaces in the attic
    Let me know if I misinterpreted any of the ESR.

  22. GBA Editor
    Martin Holladay | | #22

    I don't have the ESR in front of me, so I can't interpret it for you. But my interpretation carries no weight in this matter. The person you have to convince is your local code official, not me.

    Ask your local code official whether your intended foam installation is consistent with the ESR. If the code official agrees, you can proceed.

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