334.10(3)

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augie47

augie47

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State Electrical Inspector (Retired)
I have a metal prefab building. The G/C has framed in offices on the interior. The interior walls are 2 x 4 framing with 1/2 sheetrock, the ceiling is 2 x 6 rafters with sheetrock.
The back side of the walls face the metal building siding and have no cover.
334.10(3) calls for the cables to be "concealed within walls that provide a 15 min thermal barrier", With the back side of the walls "open" can NM be used ?
 
Therein may lie the problem:

NEC: Concealed. Rendered inaccessible by the structure or finishof the building


It's certainly inaccessible.
 
How would you treat this if the outside walls were concrete block instead of metal?
 
I see the issue that Gus is facing. The back side is open but in a sense it is not open since the ceiling has sheetrock. It appears the nm cable is not exposed and behind a thermal barrier everywhere. JMO---- I see this as compliant
 
infinity said:
How would you treat this if the outside walls were concrete block instead of metal?
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Rob, I don't know that I see a significant difference unless the wall was flush against the bock and thus "sealed"..
In the end the building inspector may be the one to wrestle with it due to draft stopping or lack thereof due to the open space behind the wall. I guess my problem is with the term concealed in walls that provide a thermal barrier. The NM is "concealed" as far as being covered on one side and inaccessible on the other. It is behind a thermal barrier (on one side).
This is fairly common construction and I had not given it a thought until recently.
 
iwire said:
So you disagree with the NEC.
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Then I must be missing something???? It is talking about interior covering(s) correct?

(3) Other structures permitted to be of Types III, IV, and V construction. Cables shall be concealed within walls, floors, or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies
 
jxofaltrds said:
Then I must be missing something????
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I think so


augie47 said:
Therein may lie the problem:

NEC: Concealed. Rendered inaccessible by the structure or finishof the building


It's certainly inaccessible.
Click to expand...

Everything is so black and white to you even when there are often other factors or opinions.

Gus is a sharp inspector, one that I feel is more concerned with commonsense than just ruling with an iron hand without care about the costs of things.

JMPO.
 
Bob are you saying the install is not compliant? The metal building on the back side would be a 15 minute barrier but I agree it is unclear where that barrier needs to be
 
augie47 said:
Therein may lie the problem:

NEC: Concealed. Rendered inaccessible by the structure or finishof the building


It's certainly inaccessible.
Click to expand...

If it is inaccessible in a void between the studded interior framing and drywall and the interior metal wall of the prefab,I would say it complies.

I t is not like ceiling spaces in joist areas that the building code because of the pitch of the roof requires an access into the space exposing the NM cable to possible physical damage.
 
augie47 said:
I have a metal prefab building. The G/C has framed in offices on the interior. The interior walls are 2 x 4 framing with 1/2 sheetrock, the ceiling is 2 x 6 rafters with sheetrock.
The back side of the walls face the metal building siding and have no cover.
334.10(3) calls for the cables to be "concealed within walls that provide a 15 min thermal barrier", With the back side of the walls "open" can NM be used ?
Click to expand...

augie47 said:
Rob, I don't know that I see a significant difference unless the wall was flush against the bock and thus "sealed"..
In the end the building inspector may be the one to wrestle with it due to draft stopping or lack thereof due to the open space behind the wall. I guess my problem is with the term concealed in walls that provide a thermal barrier. The NM is "concealed" as far as being covered on one side and inaccessible on the other. It is behind a thermal barrier (on one side).
This is fairly common construction and I had not given it a thought until recently.
Click to expand...

After re-reading your posts it now becomes clear by what you meant as "open". Some of us assumed that the wall 'touched' the exterior wall. I now read it as it does not. So the install is not code compliant.

EDIT - It is not an exterior wall then.
 
infinity said:
How would you treat this if the outside walls were concrete block instead of metal?
Click to expand...

jxofaltrds said:
After re-reading your posts it now becomes clear by what you meant as "open". Some of us assumed that the wall 'touched' the exterior wall. I now read it as it does not. So the install is not code compliant.

EDIT - It is not an exterior wall then.
Click to expand...

If I am understanding his description correctly I have seen a lot of commercial buildings with 6 in steal studded walls built with a similar void between a concrete block wall and the back side of the steel studs.

I would have no problem with someone running cable fasten on the surface of the block or on the back side of the steel joist. I would not even give it a second thought that the cable was protected.
 
I (foolishly) posted before I saw the job first hand.
(In actually have two similar jobs and I know one has a exterior metal sided building and this one.. I was trying to kill two birds with one stone with a 'generic' question.
For clarity I went this morning and took pictures (attached) of the 1st building.
JH1 shows a front view, The exterior wall is the block with the furred wall on top of the block and the interior wall 6? in front of that.

JH2 is looking down between the walls.
JH3 is looking up toward the ceiling
(click on picture for separate views)

JH1.jpgJH2.jpgJH3.jpg
 
I see one picture but this looks like a double wall. sheetrock on one side of one wall and sheetrock on one side of the other. Looks like its okay. What did they do at the ceiling where these 2 walls meet it? If it is open then there may be an issue
 
JH3.jpg
The building is an "A Frame" so the roof varies from 12' to 25 ft.
This picture is taken looking up. The left 2x6 x is the exterior wall sitting on block with OSB covering on the outside, the right 2X4 is an interior wall on slab. The gap between the two is about 6".

The building inspector has not had a panic attack as of yet :)
 
augie47 said:
That clarify anything for you, Dennis ?
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Yes, it looks open to the ceiling. I can only assume that the use of nm needing a fire barrier is to stop the spread of fire. I cannot see how this install would stop fire. It looks like a chimney to me. I also think that is a building code violation to not have any separation between the wall space and the ceiling
 
Dennis Alwon said:
Yes, it looks open to the ceiling. I can only assume that the use of nm needing a fire barrier is to stop the spread of fire. I cannot see how this install would stop fire. It looks like a chimney to me. I also think that is a building code violation to not have any separation between the wall space and the ceiling
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As so I. IF the building inspector has them seal off the opening at the top of the wall (make a fire stop) do you feel it would comply with 334 as it would have a 15 min barrier although it's in a cavity ?
 
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