15 minute thermal barrier for foam insulation

[BayPointArchitect]

Given:
2018 IBC is the applicable code. More specifically section 2603.4. A 15 minute thermal barrier is required to separate the foam plastic insulation from the interior of the building.
The foam insulation on the walls is covered with 5/8" gypsum board. But this drywall extends only a few inches above the lay-in ceiling.

Questions:
1) Is it possible to specify the one-hour fire-rated lay-in ceiling that would meet the intent of this requirement?
2) If not, then is it possible to apply a coat of intumescent paint to the exposed foam insulation?

As always, thanks in advance.

ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner

 

[Plumb-bob]

So there is rigid insulation on the walls protected by 5/8 GWB, but rigid insulation extends vertically past the GWB?

Typically a vertical fire separation needs to terminate at either a floor or roof deck, or be intersected by a continuous horizontal separation of the same or greater rating. So yes, if you have a rated tile ceiling intersecting the GWB you should be ok. But a rated tile ceiling has very specific material and instalation requirements, these need to be followed to the letter.
Or, you could have the intumescent pain applied under the supervision of an engineer or architect.
That is how i would handle it.

 

[BayPointArchitect]

Thanks Plumb Bob. Yes there is a portion of insulation on the upper wall that is exposed to the interstitial space above the lay-in ceiling.

I have never heard of the added requirement that an architect or engineer supervise the spray application of a special product. But that sounds like something that would make the remedy more likely to be accepted by the local building official.

 

[steveray]

Kind of....

[BF] 1705.15 Sprayed fire-resistant materials. Special
inspections and tests of sprayed fire-resistant materials
applied to floor, roof and wall assemblies and structural
members shall be performed in accordance with Sections
1705.15.1 through 1705.15.6.