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Fire/Flame Resistant Properites of Interior Plywood

Ryan Schultz

Ryan Schultz

Registered User
Joined
Apr 2, 2012
Messages
269
Location
Madison, WI
We have fully sprinklered, Construction Type 2B, A-3 (Assembly) facility in a 2009 IBC jurisdiction.

We have a wall assembly with exterior metal panels attached to horizontal metal girts, as illustrated on 6A/A-601 on this sheet...

https://www.dropbox.com/s/xailx9lkfuh8zqb/XSC%20-%20A-601%20-%20Section%20Details%20-%20Exterior%20Envelope.pdf?dl=0

Question,

Does the interior plywood in this wall assembly have be fire retardant, per (Section 603), or is it possible, invoking section (803.11.1) & (TABLE 803.9), for this interior plywood to simply have the following flame spreads?...

Exit enclosures and exit passageways = B

Corridors = B

Rooms and enclosed spaces = C

Here's the entire CD set, if you need it: https://www.dropbox.com/s/ffgn932orvir0c0/20150814%20-%20XSC%20-%20Permit%20Drawings.pdf.pdf?dl=0

Thanks for the Help, Ryan

OpeningDesign.com
 
If the exterior wall is not required to be fire-resistance-rated, then the finished plywood can be considered an​ interior wall and ceiling finish per subparagraph 7 of IBC Section 603.1. The plywood needs to be attached directly to the noncombustible construction (i.e. metal girts). Since this is equivalent to "set-out construction" per IBC Section 803.11.2 because of the open space between the plywood and the exterior sheathing, the plywood would need to have a Class A finish or comply with one of the three options in IBC Section 803.11.1.1. If the later, the plywood will need to have a Class B finish.

Something to keep in mind, but not applicable in this case, is if the plywood was attached to metal studs and the design of the metal-stud walls is based on composite construction by relying on the applied sheathing to give the added strength. Composite construction allows metal studs to be slightly smaller, have a greater spacing, and/or allowed to be higher without additional bracing. Since the metal studs per the composite construction method rely on sheathing applied to both sides of the studs for its strength, then the materials providing that strength should also be noncombustible (e.g. gypsum board). If the metal studs are designed based on noncomposite construction (i.e. does not rely on sheathing for the required strength), then the plywood could be applied directly to the studs just like that described above for the metal girts.
 
Thanks Ron,

Unfortunately the presiding code official does not agree.

Their view is that 803.11.1.1 only applies to interior finishes on the interior of a building, not on the interior side of an exterior wall.

Would this be your interpretation as well?
 
Have them read the definition of interior wall and ceiling finish. The definition includes a reference to interior surfaces, which is defined as surfaces that are "other than weather exposed surfaces." The inside surface of an exterior wall is an interior surface and the exposed material is the interior wall finish.
 
I see in the SECTION 603 COMBUSTIBLE MATERIAL IN TYPE I AND II CONSTRUCTION

...of the 2012 code, that there's a slight clarification, through exception: 7. Interior wall and ceiling finishes installed in accordance with Sections 801 and 803.

Do you know if there's anything in the 2009, I could use that would be in alignment with this exception 7 in the 2012 code?

Thanks Much, Ryan
 
Have them read the definition of interior wall and ceiling finish. The definition includes a reference to interior surfaces, which is defined as surfaces that are "other than weather exposed surfaces." The inside surface of an exterior wall is an interior surface and the exposed material is the interior wall finish.
Click to expand...
I'll try...

This would be a big ticket item, otherwise. :|

Thanks for the Help!

Ryan
 
Ryan Schultz said:
I see in the SECTION 603 COMBUSTIBLE MATERIAL IN TYPE I AND II CONSTRUCTION...of the 2012 code, that there's a slight clarification, through exception: 7. Interior wall and ceiling finishes installed in accordance with Sections 801 and 803.

Do you know if there's anything in the 2009, I could use that would be in alignment with this exception 7 in the 2012 code?

Thanks Much, Ryan
Click to expand...
Yes. That is what I mentioned in my first post. It's not an exception per se, but one of a number of combustible materials listed that are permitted in Type I and II construction.
 
Ryan Schultz said:
I'll try... This would be a big ticket item, otherwise. :|

Thanks for the Help!

Ryan
Click to expand...
The alternative solution is to install gypsum board. Since it is not a fire-resistance-rated wall (at least I assume it isn't), apply a 1/4" layer of gypsum board, not taped or finished, and install the finished plywood over that.
 
Darn, looks like I'll have to go through a petition. In formulating an argument, does the following make sense?...

SECTION 603 COMBUSTIBLE MATERIAL IN TYPE I AND II CONSTRUCTION

603.1 Allowable materials. Combustible materials shall be permitted in buildings of Type I or II construction in the following applications and in accordance with Sections 603.1.1 through 603.1.3:

Exception 7.


Interior wall and ceiling finishes


installed in accordance with Sections 801 and 803.


INTERIOR WALL AND CEILING FINISH.


The exposed


interior surfaces


of buildings, including but not limited to: fixed or movable walls and partitions; toilet room privacy partitions; columns; ceilings; and interior wainscoting, paneling or other finish applied structurally or for decoration, acoustical correction, surface insulation, structural fire resistance or similar purposes, but not including trim.


INTERIOR SURFACES.


Surfaces other than weather exposed surfaces.


This plywood is both exposed to the interior, and is not a weather exposed surface.
 
You'll also have to counter the argument that exterior walls are required to be of noncombustible construction per Section 602.2. Your counter argument should be that the exterior wall is nonloadbearing and does not require the installation of any applied interior material to function properly as an exterior wall--in essence, the insulation and girts could be left exposed provided they comply with the flame-spread and smoke-developed indices of Chapter 8 for the applicable finish Class. The plywood panels are added as an interior wall finish material in accordance with Subparagraph 7 of Section 603.1 and comply with Section 801 and 803, and specifically Section 803.11.2.
 
This is the perfect example of the type of great advice from knowledgeable professionals available on this forum.

Well done!
 
Agreed!....A lot of BO's get hung up on the "wood on the wall" thing in the noncombustible buildings, but if it is not structural, it is allowed. You can have a Type IIB CFMF building (metal wind and seismic bracing) with wood sheathing as long as the wood is not structural...It is basically blocking for siding.
 
kilitact said:
It might help to read/reread section 102.1. Per 2009 IBC code they are correct.
Click to expand...
Section 102.1 refers to the specific overriding the general when there is a conflict. Section 602.2, which they reference, is a general requirement, while subparagraph 7 of Section 603.1 is more specific. I don't see how Section 602.2 can be directly interpreted to mean it is an "interior sheathing"--nowhere in the Section, or even in the Chapter, does it mention "interior sheathing."

"Interior sheathing," or "sheathing" for that matter, is not defined in Chapter 2 of the IBC. IBC Section 201.4, which addresses terms not defined by the code, states that undefined terms are to have their "ordinarily accepted meanings." Sheathing, as defined in a dictionary I have, states that it is a "layer of material applied to the outer frame of a building as a base for an exterior covering." (The highlight is my own.)

Ryan:

Obviously, I still disagree with the BO's decision, but, with that said, the old adage "You can't fight City Hall" comes to mind. You can try to take it through the City's appeal process, but it will take awhile and delay things further...and you may still not win. I suggest going to my earlier recommendation and put a layer of 1/4-inch gypsum board as the so-called "interior sheathing" over the girts (don't apply tape or finish, as this will add cost; and there's nothing in the code that says you have to do it, unless it is fire-resistance-rated) and then install the plywood paneling over that per IBC Section 803.11.1 as direct attachment to the wall.
 
I would disagree with the assumption that you "cannot fight city hall". If you have valid code information, than it would appear by the communications that you received that this method would be allowed.
 
& ~ &



kilitact,

By "fighting city hall", ...the Cost - Benefit ratio comes to mind.

Yes, technically speaking one could "fight", IF they have a well

substantiated & documented case........Our opinions versus the AHJ

opinions might take an extensive length of time [ i.e. - the AHJ could

request \ take a "continuance", or two, or more ].

If **Ryan Schultz** were to add a technical opinion from ICC; in his

favor, that may add credibility to the case, but delays might cost even

more than complying with the AHJ's view \ request.

Just sayin'...

& ~ &
 
north star said:
& ~ &

kilitact,

By "fighting city hall", ...the Cost - Benefit ratio comes to mind.

Yes, technically speaking one could "fight", IF they have a well

substantiated & documented case........Our opinions versus the AHJ

opinions might take an extensive length of time [ i.e. - the AHJ could

request \ take a "continuance", or two, or more ].

If **Ryan Schultz** were to add a technical opinion from ICC; in his

favor, that may add credibility to the case, but delays might cost even

more than complying with the AHJ's view \ request.

Just sayin'...

& ~ &
Click to expand...
My point, exactly. With a well-documented case that has a very good chance of winning, the owner may still not be willing to risk the time and money to make the argument, even if the odds are in your favor.
 
Speaking from my own experience, even with ICC, a phone call in some cases helped to clarify details/information that was lost in the other forms of communications. So ten/fifteens to resolve. In this case I think the powers to be made, with the information given, made the correct call.
 
Being from WI, I find myself in agreement with your code official. His interpretation is consistent with the training I have always received, even from ICC training materials.

You can only use the direct attachment method if placing your finish material over a non-combustible surface such as drywall, or if the wall were of masonry or concrete. In this method, the backside is not exposed within the wall cavity.

Fire can attack your exposed finish material from within the wall cavity which is what direct attachment prevents. As soon as you expose the backside you have to protect it. The furring method reduces exposure by limiting the depth of the cavity to 1 3/4" and then further protecting the cavity in one of three prescribed methods. The set-out method reduces exposure by wetting both sides, placing over a non-combustible backing (eliminating exposure) or back to the furring method.

Your method of installation does not meet the "intent" of direct attachment, which is to prevent exposure of the combustible material within the wall cavity. If your wall were masonry or concrete, I would say go for it.

jmo
 
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