straping emt on a flat roof

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difowler44

Member
I was doing some work on a office building. I noticed that the wire feeding the central heat is ran in EMT. It is a flat roof, and the emt is not strapped in any way. It is just laying on the rubber mat type roof. What ever they call that stuff.

I looking for the correct method to strap the EMT to the roof. I have seen other buildings where they have made 2x4 wood supports that elevate the pipe off the roof, but they didn't have those supports screwed down to the roof. I guess you wouldn't want to penetrate the roof unless necessary.

What is the preferred method to strap EMT to a flat roof?
 
Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
We used to use roofing cement.
Those 2x4 were stuck solid. Other parts of the country it might not work!
 
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difowler44

Member
strapping emt on a flat roof

strapping emt on a flat roof

I guess just put two hole straps on the v notched 2x4 and glue it down to the rubber roof?
 
D

difowler44

Member
strapping emt on a flat roof

strapping emt on a flat roof

I have done very little commercial, but it seems that the emt would be subject to damage this way. (someone stepping on the pipe). I guess it doesn't matter on a roof. I wonder what the average height would be for the v notched 2x4 supports?
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
masterinbama said:
I have used those many times. They work well and are reasonably inexpensive.
Click to expand...

Two issues:
  1. Don't forget the temperature derating of Table 310.15(B)(3)(c) Ambient Temperature Adjustment for Circular Raceways Exposed to Sunlight on or Above Rooftops.
  2. Depends how much cursing your karma can take, but never penetrate a roof membrane. It is not a question if it will leak, the only question is when. So the C-H or any similar assembly will work well. The only problem with these in hurricane-prone areas is, that it will blow away, but gluing it to the membrane - after removing the ballast stone - will just rip the membrane too. So probably the optimal cost risk/benefit choice is to live with the potential replacement of the conduits after a hurricane, just make sure you make the Owner aware of this. (That also keeps you employed :D.)
 
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220/221

Senior Member
Location
AZ
2x4's don't far well on rooftops in AZ.

Years ago I started using short pieces of PVC and two hole straps. I use a lot of straps (one on each side of every coupling and one in the middle) and tack the PVC down with caulk (roof mastic is too freaking messy)



electrical382-1.jpg
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
In this area most commercial buildings have rubber roofing and you do not penetrate it or 'glue' anything to it.

The conduits / tubing are fasted to whatever kind of sleepers you decide to use and the sleepers just sit on the roof. If we are really on the ball we use scrap rubber roofing materiel between the sleeper and the roof.
 
chris kennedy

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
weressl said:
  1. Don't forget the temperature derating of Table 310.15(B)(3)(c) Ambient Temperature Adjustment for Circular Raceways Exposed to Sunlight on or Above Rooftops.
Click to expand...

That quote is from the 2011, as of right now we don't have to derate if tubing (EMT) is the wiring method employed.:)
 
D

difowler44

Member
strapping emt on a flat roof

strapping emt on a flat roof

It is hard not to repeat myself. You guys are just wonderful!
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
220/221 said:
2x4's don't far well on rooftops in AZ.

Years ago I started using short pieces of PVC and two hole straps. I use a lot of straps (one on each side of every coupling and one in the middle) and tack the PVC down with caulk (roof mastic is too freaking messy)



electrical382-1.jpg
Click to expand...
PVC also need to have UV retardation if it is to withstand the Arizona sun. Will not fare nearly as well as the C-H blocks.
 
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220/221

Senior Member
Location
AZ
All of the PVC I've seen over the past decade says "sunlight resistant" and I've yet to see any brittle schedule 40 PVC.

I've seen some sunbaked, blackened PVC that would shatter if hit with a hammer but, if you have someone hitting your conduit suports with a hammer, you have far worse issues.:D

The stuff is bulletproof, readily available and inexpensive.
 
J

jusme123

Senior Member
Location
NY
Occupation
JW
220/221 said:
All of the PVC I've seen over the past decade says "sunlight resistant" and I've yet to see any brittle schedule 40 PVC.

I've seen some sunbaked, blackened PVC that would shatter if hit with a hammer but, if you have someone hitting your conduit suports with a hammer, you have far worse issues.:D

The stuff is bulletproof, readily available and inexpensive.
Click to expand...

now, if it was only listed for that purpose, you would be all set
 
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