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Do I need ignition barrier for spray foam in attic kneewalls?

MattJF | Posted in General Questions on

So I outlined our attic insulation plan here, which was flash and batt with foam furring following by drywall in the occupied space:

Attic insulation details

We have had the closed cell foam installed (R22) and we are now considering the option of having 8″ (R36) open cell foam put instead of the original mineral wool. The areas that are getting drywall as a thermal barrier would still get furred with foam and strapped for drywall installation.

In the kneewalls, front dormer, and above the ceiling, the ocSPF would be left to encapsulate the framing. There is ductwork running in the front dormer (furnace soon to be ducted minisplit is within the dry walled space). Do we need an ignition barrier in these spaces?

I was thinking we would need an ignition barrier, but our installer says that we don’t. It likely isn’t enforced locally. So regardless of the inspector, what should we do?

The product we are looking at using is Demilac Agribalance. The evaluation report is here:

Section describes installation in attic spaces without an ignition barrier and I believe our situation meets all the requirements, but maybe I am missing something.

Any reasons we should stick with the original plan with mineral wool? This does seem like a lot of foam in the roof. It seems like the ocSPF should offer somewhat better performance, particularly in the awkward sections.  We go from a R35 total wall to R40 and also move the labor from me to someone else for a $.025/R/SF premium.

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  1. BrianPontolilo | | #1

    Whether you need it or not is up to the building inspector. Whether it is a good idea is another story. Here's an article all about thermal barriers and ignition barriers, that won't necessarily clear up the confusion about whether it is required, but may give you some food for thought:

  2. Expert Member
    Peter Engle | | #2

    If you can access the spaces at all, then either an ignition barrier or their intumescent paint is required. If the space can be used for storage, then the thermal barrier or thicker paint is required. If there is no access to the space, then no barrier is required.

    1. MattJF | | #3

      So I cleared up one issue:

      I had said I was trying to interpret:
      "Section describes installation in attic spaces without an ignition barrier"

      It is actually:
      "Section describes installation in attic spaces without a PRESCRIPTIVE ignition barrier"

      I forgot the paints were not prescriptive ignition barriers and thought it was describing use without any barrier.

      I am thinking I will see if the inspector brings it up in the application and then apply paint to the two knee wall spaces I foresee potentially having access doors to adjust duct dampers. These doors will require 6 screws to come out to get them open, but they are are still doors I guess.

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