Not kosher but it's what the architect/engineer wants

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karn

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Electrician
Notes on print say to mount boxes tight to roof deck, architect/engineer came out to site and even said they want conduit (EMT) one hole strapped to the deck and boxes, I understand the 1.5 inch rule with EMT, not sure on boxes, but Im sure not going to use rigid/imc, is there any other exception if the architect wants it this way, we are talking around 6-8000 ft of conduit on a good 30k sqft sales floor
 
You might aquatint him in writing with 300.4(E) which includes boxes as of the '11 Code

(There is probably a clause in the paperwork making Code requirements your responsibility)
 
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Regardless of what he wants you need to follow the code. If this installation is under the NEC then you must use RMC or IMC if they insist on screwing directly to the underside of the metal decking. You might contact the AHJ and ask about gettin a variance but in most locales that won't fly.
 
If they ever go to reroof the building, there will be breakers tripping all over the place. Those screws love to go through EMT.

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karn said:
Notes on print say to mount boxes tight to roof deck, architect/engineer came out to site and even said they want conduit (EMT) one hole strapped to the deck and boxes, I understand the 1.5 inch rule with EMT, not sure on boxes, but Im sure not going to use rigid/imc, is there any other exception if the architect wants it this way, we are talking around 6-8000 ft of conduit on a good 30k sqft sales floor
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I recently had a similar situation, but they were pouring 6" of concrete on the roof, making it a deck.
Would anyone let EMT and boxes be used in that case?
 
Hendrix said:
I recently had a similar situation, but they were pouring 6" of concrete on the roof, making it a deck.
Would anyone let EMT and boxes be used in that case?
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I would. If you don't fasten them before the concrete pour though it might not be so practical.
 
karn said:
Notes on print say to mount boxes tight to roof deck, architect/engineer came out to site and even said they want conduit (EMT) one hole strapped to the deck and boxes, I understand the 1.5 inch rule with EMT, not sure on boxes, but Im sure not going to use rigid/imc, is there any other exception if the architect wants it this way, we are talking around 6-8000 ft of conduit on a good 30k sqft sales floor
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If the architect wants the conduit mounted to the roof deck bad enough to pay for rigid then he can have his wish, if not then the conduit has to move, there is no other way around it.
 
karn said:
Notes on print say to mount boxes tight to roof deck, architect/engineer came out to site and even said they want conduit (EMT) one hole strapped to the deck and boxes, I understand the 1.5 inch rule with EMT, not sure on boxes, but Im sure not going to use rigid/imc, is there any other exception if the architect wants it this way, we are talking around 6-8000 ft of conduit on a good 30k sqft sales floor
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(E) Cables, Raceways, or Boxes Installed in or Under
Roof Decking. A cable, raceway, or box, installed in exposed
or concealed locations under metal-corrugated sheet
roof decking, shall be installed and supported so there is
not less than 38 mm (11⁄2 in.) measured from the lowest
surface of the roof decking to the top of the cable, raceway,
or box. A cable, raceway, or box shall not be installed in
concealed locations in metal-corrugated, sheet decking–
type roof.
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Is this kind of roof common? I don't recall seeing it except on storage building type structures, although maybe it was camouflaged so I didn't notice.
 
steve66 said:
But it would be a concrete roof deck, not a metal corrugated roof deck, so IMO EMT could be used.
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I'd say you have a valid point Flat roof

Though you still have a corrugated steel roof deck the application of build is a structural slab. The NEC calls out "metal-corrugated sheet roof decking" which could be considered the applicable build -- by adding concrete your assembly is no longer just "metal-corrugated sheet roof decking" which a attachment screw could not readily penetrate.
 
OP doesn't actually say it's metal decking.

I'd guess the reason for 300.4(E) is that metal roof material is typically installed with self-tapping screws that will easily drill through EMT or anything weaker. Heck, they'll drill through IMC or RMC too if you hit it just right, but more likely the roofer will notice something amiss.

When it says that a raceway shall not be installed 'in' the concealed spaces, I'd guess they have in mind the space between corrugations and whatever material the metal roofing is screwed too. When they say in concealed space 'under' the roof they are talking about a crawl or void or such that is below the roof fasteners.

mwm1752 said:
ceiling to exterior above is a roof
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Not if there's a crawl space or an attic in between, or it's a drop ceiling. I'd say leave the ceiling out of it. The code wording says 'lowest surface of the roof decking', that means on the top of the roof.
 
petersonra said:
Wouldn't the lowest surface be the bottom of the roof?
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That's not how I read it. 'Surface' meaning on top. But at any rate, it applies to 'metal corrugated sheet roof decking', which is of minimal thickness, not whatever the metal sheeting is attached to. This section doesn't apply to thicker materials like wood or concrete where it would really matter.
 
jaggedben said:
That's not how I read it. 'Surface' meaning on top. But at any rate, it applies to 'metal corrugated sheet roof decking', which is of minimal thickness, not whatever the metal sheeting is attached to. This section doesn't apply to thicker materials like wood or concrete where it would really matter.
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there are two surfaces. one on top, and one on the bottom. how could the top one be lower than the bottom one. :)
 
jaggedben said:
but more likely the roofer will notice something amiss
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One would like to think so, but, in the real world No they wont.

No more than if one was drilling through concrete and hit something hard.

Most times, one would think it was a rock and just keep drilling harder until something exploded.


JAP>
 
petersonra said:
Is this kind of roof common? I don't recall seeing it except on storage building type structures, although maybe it was camouflaged so I didn't notice.
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Go to your nearest Wal-Mart, Home Depot, or other similar roof construction buildings. The two I mentioned usually don't have a false ceiling and is easy to see the underside of roof construction. That sheet metal laying directly on top of the steel truss framing members is the roof decking that is referred to here. On top of it is a thermal insulation foam board that is fastened by driving the fasteners through that "decking". They will easily penetrate EMT and is the reason NEC now prohibits running EMT within 1.5 inches of the lowest portion of the "decking". On top of that foam is the exterior membrane - typically rubber roofing material, and possibly some other layer of material that is primarily to protect the rubber membrane from sunlight.

Typical single layer sheet metal roof (usually on wood framing members as is common on pole barn construction methods) is not the kind of roofing this "decking" is referring to. But those applications still would have the 1.25 inch from edge of framing members restrictions apply to certain wiring methods.
 
petersonra said:
there are two surfaces. one on top, and one on the bottom. how could the top one be lower than the bottom one. :)
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From dictionary.com

surface
[sur-fis]
noun
1. the outer face, outside, or exterior boundary of a thing; outermost or uppermost layer or area.
2. any face of a body or thing:
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So you see, either of us could be right. My definition is the first one though. :p
 
petersonra said:
there are two surfaces. one on top, and one on the bottom. how could the top one be lower than the bottom one. :)
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becauase of the corrugated design, it doesn't have a finished surface with an even plane, we need to keep most wiring methods 1.5 inches away from the lowest plane so any fasteners from above don't damage those wiring methods. RMC/IMC are about the only methods allowed to be directly mounted to it.
 
rubber on top

rubber on top

petersonra said:
Is this kind of roof common? I don't recall seeing it except on storage building type structures, although maybe it was camouflaged so I didn't notice.
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My plant has it with a rubber roof on top. I have seen it also with tar and stone chips on top of the metal.
 
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