Blocking vs location in walls

[Examiner]

Given Construction Type II-B with automatic fire suppression system

Code 2012 IBC

I have been reviewing a project. I was asked to review the partition types and check them. I came across one that had all wall surfacing materials on one face of the stud.

Composition goes like this;

Starting at outer wall skin side on room; Sheetrock to 10-ft AFF, fastened to ¾” FRTW plywood, fastened to the metal stud and above the plywood 5/8” sheetrock continues to the bottom of the structural deck fastened to the metal stud. So, you have one side of the stud without any wall surfacing material which faces a big void space that is not accessible to service a sprinkler head.

Since the void space has another similar partition composition, minus the plywood, about 5-ft away; the plywood on one partition is in a concealed space and not a wall cavity. Type II-B does allow FRTW for interior non-bearing walls but FRTW is still a combustible material. The plywood is being used as blocking, but to avoid locating the required blocking precisely, the designer wanted a full sheet of plywood. Even if it was wood blocking or furring strips, they would have to be in the wall cavity and enclosed with a thermal barrier.

So, I was asked; if the material to be used as a nailable material and had a Class A flamespread would it still have to be enclosed? My answer was yes, if it was still a combustible product, because FRTW is still combustible. I do not think they can get any plywood to be a Class A material anyway.

I instructed the person doing the partition details to provide a full height layer of sheetrock on the one stud face then the plywood with at least 12” of sheetrock above the plywood and then another layer of sheetrock to extend 6” above the plywood’s top joint. That way the plywood is fully encased in a thermal barrier. Or provide another full height run of sheetrock on the other face of the stud.

Comments anyone.

 

[steveray]

No limit to the amount of combustible blocking in IIB construction.....But I am not really sure of your install situation...Sketch a pic? There are several exceptions in NFPA 13 for omitting sprinklers...

 

[Examiner]

That is the problem with NFPA 13 and the Building Code. The Building Code overrules referenced standards when there are conflicts; covered in Chapter 1. Example; the Designer states that the local Fire Marshall wants the electrical panel room to be enclosed with 2-hr rated walls per NFPA 13. I told the Designer that I am aware of the ongoing issue with sprinkler heads in an electrical room which verbiage has changed almost every edition. However, the reference to enclosure is not just the walls but the floor and ceilings have to be rated. I guess the Fire Marshall does not know that references to a rated enclosure is more than just the walls. The IBC in Chapter 9 clearly states that the sprinklers are NOT required in electrical rooms even if they are rated. The IBC in Chapter 9 addresses the rated enclosure for only Generator and Transformer rooms not the electrical panel room. Thus the conflict between the two which the IBC overrules the NFPA 13. However, this is not addressing the combustible material in the concealed space which is addressed in the code. The material is being used as blocking and occurs in a concealed space. Combustible blocking has to occurred within the wall's cavity where it is encased with a thermal barrier such as sheetrock. Yes, combustible blocking is allowed in Type II-B but it is not allowed to be exposed in concealed spaces. Kind of like when using fire retardant wood for the roof's construction in the roof's attic. It is a concealed space and as such will require fire suppression in the space. If the combustible blocking is not encased in the wall's cavity then it is exposed in a concealed space. If the concealed space is not accessible to service the fire suppression then there lies the problem. To comply with the code the exposed combustible blocking in the concealed space will have to be in the wall's cavity enclosed by the wall's thermal barriers (sheetrock) or encased in thermal barriers. Sandwiching the FRTW plywood between the thermal barriers provides the encasement of the combustible material same as if it was encased in the studs cavity.

 

[steveray]

Really bad job on this for some reason, but IBC does not exempt electrical rooms.



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[Examiner]

Yes, I know that the IBC overrules the NFPA 13 on electrical panel rooms, but I have a City's Fire Marshall that thinks the electrical room must comply with NFPA 13 and he also thinks that the enclosure is only 2-hr fire rated walls. I have told my bosses the pros and cons regarding this. An enclosure as addressed in the NFPA 13 and in the IBC is not only the walls but ceiling and floor. Since one electrical room is on a upper floor there lies the problem with rating the floor under the electrical room. Per the IBC you have to do the entire floor being supported from column grid to column gird. Even a legal opinion years ago on another project regarding another code section was given to an AHJ, "that if you think that there is a Code issue then you have to comply with the full requirements of the Code". The AHJ was in error and had to rescind what they were wanting the Building Owner to do. The bosses just do not want to show the Fire Marshall and Building Official that they are misunderstanding the requirements. On another issue, I have a friend who has a Fire Marshall that thinks the requirement of luminous egress path markings applies to all buildings. As is the case with many in the Architectural field they do not want to try and get the AHJ to understand the Code for fear they will just make matters worse. It is a sad day when an AHJ does not want to know they maybe in error regarding an code section.

 

[Francis Vineyard]

Regardless if another layer of drywall is applied to the other side; or the adjacent wall forms a concealed space; as you mentioned the FRT wood it is considered to be combustible (Ref ASTM E136). As such combustible concealed space is formed; fireblocking is required.