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Exterior Wall Coverings - Combustible???

mp25

Registered User
Joined
Jun 2, 2016
Messages
107
Location
Illinois
Given:

2015 IBC
Type III building, 80' high.

Definition of Exterior Wall Coverings: A material or assembly of materials applied on the exterior side of exterior walls for the purpose of providing a weather-resisting barrier, insulation or for aesthetics, including but not limited to, veneers, siding, exterior insulation and finish systems, architectural trim and embellishments such as cornices, soffits, facias, gutters and leaders.

Exterior wall is fire resistance rated (gypsum board, FRTW wood studs, gypsum board). Over the exterior gypsum board, a water resistive barrier is applied (tyvek), then FRTW furring strips, and a fiber cement panel.

Question:

Is this considered a combustible exterior wall covering? Does the "exterior wall covering include everything beyond the exterior layer of the gypsum board? or just the material that is exposed on the exterior of the wall (in this case the fiber cement panel)?

Reason for question is to see if 1406 applies. I read the commentary but I did not getting any additional clarity on the matter.
 
With a height of 80 feet, then I am guessing that this must be Type 3A construction which allows a maximum height of 85 feet for residential occupancies.
Regardless of what the code allows, this is not a good idea.
Exterior walls for Type III construction must be constructed of noncombustible materials such as metal studs. The exception allows for fire-retardant-treated wood framing. For Type III, we typically see the two-hour fire-rated exterior walls constructed using FRTW wood studs and FRTW exterior plywood (the pink stuff).
 
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With a height of 80 feet, then I am guessing that this must be Type 3A construction which allows a maximum height of 85 feet for residential occupancies.
Regardless of what the code allows, this is not a good idea.
Exterior walls for Type III construction must be constructed of noncombustible materials such as metal studs. The exception allows for fire-retardant-treated wood framing. For Type III, we typically see the two-hour fire-rated exterior walls constructed using FRTW wood studs and FRTW exterior plywood (the pink stuff).
You should stop replying to Type III Posts. You very clearly have no experience in this building type. Hardie is a VERY common cladding in Type III buildings. Please show me an example where fiber cement panels have contributed to fire propagation in a Type II building.
 
You should stop replying to Type III Posts. You very clearly have no experience in this building type. Hardie is a VERY common cladding in Type III buildings. Please show me an example where fiber cement panels have contributed to fire propagation in a Type II building.
They don't, but the combustible sheathing and furring strips will...

And you may want to look at this section as well:

1403.5 Vertical and lateral flame propagation. Exterior
walls on buildings of Type I, II, III or IV construction that are
greater than 40 feet (12 192 mm) in height above grade plane
and contain a combustible water-resistive barrier shall be
tested in accordance with and comply with the acceptance
criteria of NFPA 285. For the purposes of this section, fenestration
products and flashing of fenestration products shall
not be considered part of the water-resistive barrier.
 
"You should stop replying to Type III Posts. You very clearly have no experience in this building type."

I don't see where BayPointArchitect's answer contradicted the code, and he said what he typically sees. I personally wouldn't want to design such a building, but it does meet the code as long as the exterior wall has a 2-hour rating.
 
They don't, but the combustible sheathing and furring strips will...

And you may want to look at this section as well:

1403.5 Vertical and lateral flame propagation. Exterior
walls on buildings of Type I, II, III or IV construction that are
greater than 40 feet (12 192 mm) in height above grade plane
and contain a combustible water-resistive barrier shall be
tested in accordance with and comply with the acceptance
criteria of NFPA 285. For the purposes of this section, fenestration
products and flashing of fenestration products shall
not be considered part of the water-resistive barrier.
The sheathing is covered in 602.3 since it is part of the assembly. The furring is a matter for debate, often it is steel hat channels in Type III but many AHJs allow FRTW furring in Type III.

And, yes, NFPA 285 applies to Type III.
 
"You should stop replying to Type III Posts. You very clearly have no experience in this building type."

I don't see where BayPointArchitect's answer contradicted the code, and he said what he typically sees. I personally wouldn't want to design such a building, but it does meet the code as long as the exterior wall has a 2-hour rating.
It's not just this post. From other posts it is evident he may have seen some Type III buildings but has not been involved in their design or construction. He is hung up on the idea that wood should not be used in Type III despite what the code and common practice allows. But his opinion is academic. Wood burns=bad. OK, well we have FRTW, gyp fire protection, compartmentalization of fire, fire sprinkler requirements, multiple egress path requirements, and on and on. In the real world, Type III projects are wood framed with FRTW exterior walls and they are safe.
 
The sheathing is covered in 602.3 since it is part of the assembly. The furring is a matter for debate, often it is steel hat channels in Type III but many AHJs allow FRTW furring in Type III.

And, yes, NFPA 285 applies to Type III.
Yes...but FRTW is not non-combustible so it is a concealed combustible space...OP says FRTW furring and that will have it's own issues to deal with...
 
I agree with others, the FRTW is a combustible material--just not as combustible as untreated.

And the code says wall assembly. The cladding and furring must be part of the NFPA 285 wall assembly.
Definitely, but the question remains: has this assembly been tested? If not, then they must have it tested. To avoid the NFPA 285 test, switch the furring from FRTW to metal furring. Then, all that remains is to make sure the WRB complies with either Exception 1 or 2 of Section 1402.5.
 
Thank you for brining my attention to 1403.5 / NFPA 285. I will have to find out if this assembly was tested.
This was originally designed with metal furring, but now the plan is to substitute it with FRTW which was the reason for my question.

Having said that, I am still not clear about which components of the wall assembly would be considered part of the Exterior Wall Covering. If the wood furring is part of the exterior wall covering then section 1406.2.1 would limit its use to 60 feet above ground and above 60 feet the furring would have to be non-combustible. If the exterior wall covering would only include the outermost surface of the wall covering (i.e. Fiber cement), then the exterior wall covering would be considered non-combustible and 1406.2.1 would not apply. I am leaning towards one of those two but I see arguments for looking at it either way.
 
I am still not clear about which components of the wall assembly would be considered part of the Exterior Wall Covering.
The definition for an exterior wall covering states that it is the "assembly of materials applied on the exterior side of exterior walls for the purpose of providing a weather-resisting barrier, insulation or for aesthetics..."

The exterior wall stops at the exterior sheathing for framed walls. Everything that is added to the wall, from the sheathing on out, is part of the exterior wall covering.
 
And I guess you get out of fireblocking if you meet NFPA 285.....

3. Fireblocking shall not be required where the
exterior wall covering has been tested in accordance
with, and complies with the acceptance criteria
of, NFPA 285.


Let us know how this shakes out....
 
I got an NFPA 285 report that allows for the exterior veneer to be "fiber cement siding or fiber cement panels (noncombustible). Minimum 1/4" - any standard installation technique can be used." Checked out the ESR report for the specific fiber cement panel and they do allow for installation over wood furring that is 3/4" x 3 1/2"... so that sounds like installation over FRTW furring would qualify as a standard installation technique.
 
I got an NFPA 285 report that allows for the exterior veneer to be "fiber cement siding or fiber cement panels (noncombustible). Minimum 1/4" - any standard installation technique can be used." Checked out the ESR report for the specific fiber cement panel and they do allow for installation over wood furring that is 3/4" x 3 1/2"... so that sounds like installation over FRTW furring would qualify as a standard installation technique.
Make sure you read the window opening detailing of your NFPA 285 assembly. Everyone seems to miss that part... and it's the most important aspect of the assembly to meet the testing requirements.
 
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