Rating of Stone Masonry Wall?

[Dave in WI]

I have a situation where it would be beneficial to consider an existing 12" thick stone masonry wall as 1-hour rated. The wall is made up of 4"-8" diameter stone (no idea what KIND of stone) solidly mortared together to a roughly 12" thickness.

(The reason why it would be good to consider it rated is for the installation of a handicapped accessible lift. It would be installed in a "notch" in the building, and it would JUST fit if we skim coat the existing stone wall. If we need to furr it out with gypsum board or shaftwall, it won't fit, it's that close. 708 requires a shaft to be 1-hour rated for this, a 2-story building.)

I've looked at calculated resistance in IBC, and the ratings of archaic materials in IEBC. However those generally address CMU, brick or clay tile masonry, not stone.

Common sense tells me that if this building were to burn down, this stone wall would be the only thing left standing. However I would like to be able to go to the AHJ with something to point to besides this. Anyone have any ideas, ever run across this before?

 

[JPohling]

an access lift? are you sure it is in a shaft?

 

[JBI]

Ask an old time stone mason? I tend to agree that GWB won't enhance anything in this case.

 

[cda]

Consider it concrete??

Guess a question is will it hold together?

Ask the ahj if they will accept it as rated?

 

[steveray]

Nothing "concrete" in the code (pun fully intended)....I am sure we would find a way to accept it if it was sound construction...

 

[mtlogcabin]

12" thick stone masonry wall

Certain types of stone can explode when heated so it is a legitimate question even though it is 12 inches thick.

Perhaps a geologist can determine the type of stone used and aid in determining how much heat it can take.

 

[Paul Sweet]

I believe that equivalent thickness tables for concrete & block have different thicknesses for different aggregates. I think it should only take 4" or so for a 1-hour rating, even for granite (which is the most likely to pop corners off in a fire.

My main concern would be how solid the stonework is. It was common to lay the stones fairly loosely and not fill all the spaces inside the wall with mortar.

 

[Dave in WI]

an access lift? are you sure it is in a shaft?

I think that's the real question, does it need to be a rated shaft? We called the plan reviewer and he said read chapter 7, it will tell you where a shaft is needed.

708.2 says shafts are required where a floor/ceiling assembly is penetrated.

It's a stretch but we could say we are not penetrating a floor/ceiling assembly since the footprint of the lift will be outside the building, with openings into the building through what were exterior walls. However an enclosure will be built.

The only exception I can see allying may be 7, although it's debatable if it opens onto a corridor. I know, a plan or pictures sure would help.

 

[steveray]

If you are putting a roof over it, it is inside the building, and a shaft...