Jeff Tock of Allegion sent me this photo of a fire door assembly where it looks like the frame was supplied with a jamb depth that was too large. To make up the difference between the throat of the frame and the wall thickness, wood was added between the return on the frame and the face of the wall.
This fire door assembly is in a stairwell, and in my opinion the use of the oversized jamb and wood filler strips is not acceptable. I haven’t been able to find a specific paragraph in a code or standard that addresses this…the best I could see (or not see) was the absence of anything in a standard that would allow this installation method.
According to UL, this application would have to be tested or evaluated by a listing lab prior to installation. I also spoke to one of my contacts from BHMA, who cited NFPA 80’s requirement that fire door assemblies can be installed in “walls of other construction” only when they are listed for that installation.
If I found this application in the field, I would contact the frame manufacturer and see if the application is allowed by their listing. I’m pretty sure the answer would be “no.” Based on the fire tests I’ve seen, this installation could seriously impact the ability of the assembly to withstand smoke and flames.