malachi constant
Senior Member
- Location
- Minneapolis
NEC 2011, 300.4(E) states:
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300.4 (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 1 ?? 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.
Information Note: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screw or other mechanical devices designed to provide ?hold down? strength of the waterproof membrane or roof insulating material.
Exception: Rigid metal conduit and intermediate metal conduit shall not be required to comply with 300.4(E).
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I am an engineer working with an architect on a high-end space, ceilings are open to deck. He wants pendants on the ceiling with no exposed conduits. Looks like we can hide IMC or rigid in the roof deck per code. But what about boxes for the pendants? Do those need dropped down 1.5" below lowest surface of roof decking?
I believe there is a level of acoustic treatment on the underside of the roof deck - one of those corrugated metal looking things. I am not very familiar with structural assemblies - would that acoustical treatment be considered part of the roof deck system? What I'm getting at is if the acoustical system is 1.5" thick and not considered part of the deck then the box could be surface mounted to the bottom of it.
Also - looking at a cost estimating catalog, it appears IMC is about $4/LF more (installed) than EMT. This would be work done on a lift (is a two-story area). To me this does not seem to be a siginificant cost. 500LF IMC at $4/LF works out to $2000, plus a little premium for lift work, is a drop in the bucket on an $8M project. I am not talking crazy, right?
Any thoughts are appreciated. Thanks!
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300.4 (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 1 ?? 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.
Information Note: Roof decking material is often repaired or replaced after the initial raceway or cabling and roofing installation and may be penetrated by the screw or other mechanical devices designed to provide ?hold down? strength of the waterproof membrane or roof insulating material.
Exception: Rigid metal conduit and intermediate metal conduit shall not be required to comply with 300.4(E).
----------
I am an engineer working with an architect on a high-end space, ceilings are open to deck. He wants pendants on the ceiling with no exposed conduits. Looks like we can hide IMC or rigid in the roof deck per code. But what about boxes for the pendants? Do those need dropped down 1.5" below lowest surface of roof decking?
I believe there is a level of acoustic treatment on the underside of the roof deck - one of those corrugated metal looking things. I am not very familiar with structural assemblies - would that acoustical treatment be considered part of the roof deck system? What I'm getting at is if the acoustical system is 1.5" thick and not considered part of the deck then the box could be surface mounted to the bottom of it.
Also - looking at a cost estimating catalog, it appears IMC is about $4/LF more (installed) than EMT. This would be work done on a lift (is a two-story area). To me this does not seem to be a siginificant cost. 500LF IMC at $4/LF works out to $2000, plus a little premium for lift work, is a drop in the bucket on an $8M project. I am not talking crazy, right?
Any thoughts are appreciated. Thanks!
