# Noncombustible Sheathing



## ArchATL (Jun 14, 2010)

IBC 2006, Article 705.5, Exception 3 states in part "Fire walls shall be permitted to terminate at the interior surface of noncombustible sheathing...."

Question: What is an approved noncombustible sheathing? Glass Mat Sheathing?


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## bldginsp (Jun 14, 2010)

We have seen gypsum used as noncombustible sheathing.  Contrary to what the contractors believe fire retardant or treated is NOT noncombustible sheathing.


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## Mule (Jun 14, 2010)

Some information from the APA on fire retardent treated plywood.

Fire Retardent Treated Plywood


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## Yikes (Jun 15, 2010)

Check out this alternative - - a fire-rated OSB sheathing:

http://www.lpcorp.com/flameblock/


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## mtlogcabin (Jun 15, 2010)

Although the following is from the IMC it confirms what bldginsp stated "fire retardant or treated is NOT noncombustible sheathing".

NONCOMBUSTIBLE MATERIALS. Materials that, when tested in accordance with ASTM E 136, have at least three of four specimens tested meeting all of the following criteria:

1. The recorded temperature of the surface and interior thermocouples shall not at any time during the test rise more than 54ºF (30ºC) above the furnace temperature at the beginning of the test.

2. There shall not be flaming from the specimen after the first 30 seconds.

3. If the weight loss of the specimen during testing exceeds 50 percent, the recorded temperature of the surface and interior thermocouples shall not at any time during the test rise above the furnace air temperature at the beginning of the test, and there shall not be flaming of the specimen.


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## peach (Jun 15, 2010)

hmmmm... it seems that if FRT plywood can't show any signficant fire progress in 20 minutes.. it's not going to in the first 30 seconds..

maybe it's just me


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## beach (Jun 15, 2010)

What bldinsp and mtL said.........although I wouldn't consider gypsum board to be non combustible either


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## texasbo (Jun 15, 2010)

Gyp sheathing and other gyp products have been tested to E136 as noncombustible. Have yet to see a FRT wood product successfully pass E136 and classified as noncombustible.

As an interesting hijack, how many of you remember the heated discussion on the old ICC boards regarding aluminum storefront and its lack of testing to E136? Epic.


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## beach (Jun 15, 2010)

Does the code or for that matter, do inspectors.... allow gyp board to run tight to a B vent? Would you allow drywall to run tight around a fireplace opening? I have never allowed it because I was always under the impression that drywall was rated, but not truly noncombustible such as cement board, tile, etc. Have I been making the wrong call all these years?

EDIT: Actually, I just found the answer to my question in the definitions.....

Edit again: I don't believe paper faced gyp wallboard has passed E136........


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## texasbo (Jun 15, 2010)

Section 602.2, 2006 IBC requires many elements of Type I and Type II construction to be of noncombustible materials. There are exceptions of course, that allow combustible construction.  For those elements that must be noncombustible, do you allow gypsum wallboard to be used? For instance on walls and floor/ceiling assemblies?


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## ArchATL (Jun 16, 2010)

Goes back to my original question - inspector not allowing ANY plywood (even FRT), gypsum or glass mat product so what is non-combustible sheathing? Metal plates?


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## texasbo (Jun 16, 2010)

I would (and have) allowed gyp sheathing. However, I may be alone in my interpretation.


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## beach (Jun 16, 2010)

> Section 602.2, 2006 IBC requires many elements of Type I and Type II construction to be of noncombustible materials. There are exceptions of course, that allow combustible construction. For those elements that must be noncombustible, do you allow gypsum wallboard to be used? For instance on walls and floor/ceiling assemblies?


"Building element" as defined in section 702: "A fundamental component of building construction, listed in Table 601, which may or may not be of fire - resistive-rated construction and is constructed of materials based on the building type of construction"

I don't believe gypsum wallboard is an element that is required to be non-combustible... I would consider it part of a "Fire-resistance rated" assembly or "Fire Barrier" as defined in section 702.

As you said earlier, gypsum wallboard must pass E136 to be rated as "Non-combustible" and I don't think it has passed due to the paper face on typical gyp wallboard.

I believe gyp wallboard is considered "Limited non-combustible", meaninig it can be used in some instances and not in others.......


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## texasbo (Jun 16, 2010)

beach said:
			
		

> I don't believe gypsum wallboard is an element that is required to be non-combustible... I would consider it part of a "Fire-resistance rated" assembly or "Fire Barrier" as defined in section 702.


Actually, per 602.2, which references Table 601, "building elements" in Type I and II construction must be of noncombustible materials. We're not talking about fire walls or fire barriers here; let's not confuse fire resistive assemblies with noncombustible assemblies.

A wall (or ceiling, or other element in Table 601) must be noncombustible in Type I or Type II construction. Do you allow gypsum wallboard in these nonrated assemblies that are required to be noncombustible?

Gypsum wallboard has been tested to E-136:  http://www.gypsum.org/pdf/GA-235-05b.pdf

The paper facing argument is not without merit. The argument could be made, however, that the paper is an interior finish, which is exempt per 801.1.1, exception 1.

I'm comfortable not having to rationalize it using that argument, however, just as you and I both are comfortable allowing it for walls and ceilings in Type I and Type II construction.

And since you and I (and every other member of this forum) are already allowing gyp wallboard in assemblies that are required to be noncombustible, isn't it fair to also consider gyp sheathing noncombustible?


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## beach (Jun 16, 2010)

Texasbo,

I agree it is fair to consider gyp board as noncombustible in most instances, however.... the definition of noncombustible is slightly different in the mechanical code: "...Material required to be noncombustible for reduced clearances to flues, heating appliances, or other sources of high temperature shall refer to material conforming to 1 above."   "1 above" is "material at which no part will ignite and burn when subjected to fire" which leaves gyp board out.

So, I believe gyp board cannot be truly "noncombustible". As I stated before I think it is now considered "limited noncombustible".

But for the sake of argument, you are correct, sir!


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## AegisFPE (Jun 16, 2010)

Another angle to the OP, Exception 3 to 705.5 does not say "where the building exterior is wholly sheathed in noncombustible material," but only that the firewall must "terminate" at noncombustible sheathing.  The extent of noncombustible sheathing to be provided may also be up for discussion.


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## Plans Approver (Jun 17, 2010)

Gypsum board is considered a composite material by IBC 703.4.2. A non-combustible base material (gypsum) and facing less than 1/8" thick with an FSI less than 50 which includes most gypsum board panels. Composite materials do not need to meet ASTM E-136, but, rather ASTM E-84.  So it can be used as the termination of a firewall. The noncombustible sheathing must extend 4 feet on each side of the firewall (705.5.1).

In the IMC, composite materials are not considered non-combustible with regard to clearances for flues and other high temperature equipment. But, they are allowed in plenums.

"Limited combustible" is the description in NFPA Codes, especially 13.


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## peach (Jun 17, 2010)

Did the OP ever say it was a type 1 or 2 building?

If the whole building is combustible construction, what difference does it make whether the sheating is FRT or anything else?


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## Plans Approver (Jun 17, 2010)

peach said:
			
		

> If the whole building is combustible construction, what difference does it make whether the sheating is FRT or anything else?


It does matter. Firewalls (705.5) are to continue to 18" beyond the exterior wall. Exception 1 permit the fire wall to terminate at combustible sheathing if the exterior wall has a 1 hour rating for 4 feet on both side of the firewall.  The 3 exceptions to 705.5 give relief from the 18" extension. 705.5.1 reiterates 705.5 Exception 1 (and in a way Exception 2)  except at firewalls that intersect at 180 degrees or more.

The OP asked what is non-combustible sheathing? It went off course from there.


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## Glennman CBO (Jun 18, 2010)

Beach said: So, I believe gyp board cannot be truly "noncombustible". As I stated before I think it is now considered "limited noncombustible".

Texasbo said: The paper facing argument is not without merit. The argument could be made, however, that the paper is an interior finish, which is exempt per 801.1.1, exception 1.

I agree. Gyp board is a "limited combustible". These arguements are consistent with NFPA 13 "limited combustible" (I know it is only a standard). The paper face being laminated to the gypsum gives it a substantial limitation to its combustibility and fits 801.1.1. However, you can go so far as to call the gyp board non-combustible per Plans Approver's arguement from 703.4.2 as ling as it meets ASTM E-84 testing, since it is a composite.


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## ArchATL (Jun 22, 2010)

Yes - my original question was what is non-combustible sheathing?

FRT - NO

Gypsum Sheathing - looks like NO

Glass Mat Sheathing - Maybe

Cementitious Sheathing Board - Don't Know

What other choices are there?


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## Examiner (Jun 22, 2010)

Info from the product Data Sheet

Dens-Glass® Gold is a unique, ‘‘paperless’’ sheathing panel made of a patented water resistant and silicone-treated core, surfaced with glass mat facings and a ‘‘gold’’ colored alkali-resistant coating.

Dens-Glass Gold exceeds ASTM E 283 and E 331 test criteria for both Air Infiltration and Static Water penetration with approved joint finish methods as alternates to building felts.

Dens-Glass Gold panels provide 0 flame spread, 0 smoke developed when tested in accordance with ASTM E 84.

Noncombustible when tested in accordance with ASTM E 136.

Dens-Glass Gold exceeds ASTM C 79 standards for humidified deflection by a factor of 10 in tests over the standard for regular gypsum sheathing.


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## MarkRandall (Jun 23, 2010)

This is an interesting discussion. Looks to me like it's best to use metal decking and not try to look at alternates. I'd never use any type of gypsum product for a roof deck material even if my engineer said it could transfer the required lateral load. I can see headlines in the newspaper...construction worker dies falling through roof sheathing. I've never check cementitious board for horizontal span rating, but it certainly doesn't sound like a good idea.


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## Examiner (Jun 24, 2010)

I thought the discussion was about wall sheathing not roof decking.


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