A Question that has come my way

[Pierre C Belarge]

Location - Rooftop:

A contractor wants to install PVC on top of the rubber roof, but below/within/covered by the gravel. The rooftop will be open to pedestrians, so they will be walking on this area.(Public Space)


Question:

1.What would you require as far as protection from physical damage?

2. What about the ambient temperature, not according to the table added in 310 of the 2008?

3. Any other considerations?

 

[barbeer]

First I would think that sch. 80 was justified.

How would they secure and support the conduit?

I have not brushed up on the ambient temp table yet!

IMHO it could be do-able.

 

[ceb58]

Location - Rooftop:

A contractor wants to install PVC on top of the rubber roof, but below/within/covered by the gravel. The rooftop will be open to pedestrians, so they will be walking on this area.(Public Space)


Question:

1.What would you require as far as protection from physical damage?

2. What about the ambient temperature, not according to the table added in 310 of the 2008?

3. Any other considerations?

This is a strange one. The only thing I can think of is I have never seen gravel spread thick enough that it would cover the conduit. I think I would rather see it in ridged due to the foot traffic on the gravel on top of pvc.

 

[RUWired]

The rooftop will be open to pedestrians, so they will be walking on this area.(Public Space)


Question:

1.What would you require as far as protection from physical damage?

2. What about the ambient temperature, not according to the table added in 310 of the 2008?

3. Any other considerations?

1. I would consider the entire roof as subject to damage because it does not have any designated walking areas and the stones could actually puncture the pvc quicker than without the stones especially in colder climates.
2. Why don't you want to use table 310.15(B)2(C)?
3.What about supporting the conduit. 352.30 requires a secure support. The stones on the roof cannot provide this.
Rick

 

[Cow]

We have a hospital here with smooth river rock on the roof, it must be a 4-6" thick layer. If his roof is similar, I don't see a problem with it if he installs the necessary amount of expansion joints and runs sch. 80. I think it meets the fastening requirements too, it's no different then using the earth as a support IMO.

 

[RUWired]

We have a hospital here with smooth river rock on the roof, it must be a 4-6" thick layer. If his roof is similar, I don't see a problem with it if he installs the necessary amount of expansion joints and runs sch. 80. I think it meets the fastening requirements too, it's no different then using the earth as a support IMO.

Cow, If you want to go the cover meets the support requirement, i think then table 300.5 would have to come into play.JMO.
The only problem i see is if it's just one conduit one might say no big deal, it's no different than putting a 4 x 4 under the run with a strap on it, but then someone adds another and another. It gets out of hand, then the roofer comes in....My thoughts are install a support system from the start and build from there.

Rick

 

[jrannis]

Can the conduit be boxed in somehow? Something like brick on the sides and 12x12 concrete stepping stones mortered in place on top?

 

[iaov]

Isn't there a requirement that the conduit be supported a certain distance off the roof do to temp?? Also if foot traffic is involved I would highly recommend RMC.

 

[Jim W in Tampa]

Being this is outside i think bariel depth must apply. So i would need 18 inches of rock. How is this any differant than gravel in a yard ? I think its a no go unless ran exsposed

 

[KevinVost]

IMO, Schd 80 at least, properly supported (if you could get RMC, better), however I don't think part of the intent of 300.5 is to require cover at this location. The intent of 300.5 is to prevent damage to the conduit or raceway from a shovel/machine etc. A few inches of gravel cover on a roof where it is highly unlikely that anyone will use a shovel or tool (since it is a rubber roof under the stone) to move rocks, should not be a problem. I know some will disagree, but the AHJ should make the determination (our AHJ has allowed this in the past). Going back to the PVC, if there is going to be pedistrian foot traffic (public), I would rather see RMC but schd 80 meets the requirement.

On a side note, if the roof is a public space, they will be required to have egress paths, if so I believe the IBC requires a smooth walking surface for exiting. (I know this is not an electric requirement but it is something to be aware of and you may be able to use it, say if a walk way is required, the raceway could be run under it.)

 

[Pierre C Belarge]

This is an unusual installation request/question.

The responses are some of the same questions I have going through my mind.

I want to be able to provide this gentleman with an answer Monday or Tuesday...You guys don't have long to come up with an answer for me!!! :grin: Lets start mind-melding, lets goooooooo:grin:.

 

[Jim W in Tampa]

This is an unusual installation request/question.

The responses are some of the same questions I have going through my mind.

I want to be able to provide this gentleman with an answer Monday or Tuesday...You guys don't have long to come up with an answer for me!!! :grin: Lets start mind-melding, lets goooooooo:grin:.

You have plenty of code numbers to say no to this. Let him come up with answers to say they dont apply. I see liability involved here, lets be sure its all his and not yours. Just how many inches of rock are we talking ? If only a few i see it easily kicked around by kids and then maybe trip hazard. I agree a shovel wont get it but nec says barried. Does this only apply to ground level ?

 

[teco]

I think its unrealistic to think the pvc will remain under gravel cover for long if the actual conduit area is exposed to foot traffic kicking the gravel around. I've seen many roofs where the rubber shows through gravel areas just from the foot traffic of various trades. A pvc would never survive in some areas i've seen. IMO

 

[radiopet]

I don't see where you could prohibit SCH.80 from this application as it is clearly accepted as a means of protection from physical damage. However, It would need to be secured properly because in my opinion it is not considered a "Buried Conduit" as I would regard in the use of 300.5 and with that I agree that in regards to the cover of gravel on a roof with intended traffic that indeed portions of this conduit will be exposed to the sun and would envoke the requirements of 310.15.(B)(2)(c) in the adjustment.

(4) Enclosure or Raceway Damage. Where the enclosure
or raceway is subject to physical damage, the conductors
shall be installed in rigid metal conduit, intermediate metal
conduit, Schedule 80 PVC conduit, or equivalent.

 

[wireguru]

I dont know what this is for, or what is in the conduit, but what about this:

Use the parking lot MC cable that can be embedded in concrete, lay it on the roof, pour a hump of lightweight concrete over it, then have the gravel placed.

 

[Pierre C Belarge]

When I come across an installation that is "unusual", I try to look at it in as many different angles as I can, hence my visit here with the question.
It is better to use many minds than just mine.
I do have an idea, yet I still want to see what else others come up with.

 

[Jim W in Tampa]

When I come across an installation that is "unusual", I try to look at it in as many different angles as I can, hence my visit here with the question.
It is better to use many minds than just mine.
I do have an idea, yet I still want to see what else others come up with.

I would suggest visiting the site if its your name saying ok. Words never replace actually seeing. At best this is in gray area. Very sure you will apply thinking as to is this safe. Lets see pictures.

 

[whillis]

This wouldn't be a green roof, would it?

We've done a number of green roof installations that had an instrumentation set-up to record the environmental conditions and the heat transfer to/from the building. In all cases there was a need to have conduit running across roof areas where there would be pedestrian traffic from the people who maintained the install. Usually, paths were defined and we ran the conduit (schedule 80 PVC) outside the areas where people would be walking. If we couldn't do that we built a treated wood berm that would cover and protect the conduit and be level with the gravel/dirt.

 

[cadpoint]

I think it's a viable hole in appliable codes, I've done two different installs, I'll hold my comments...

 

[Pierre C Belarge]

I think it's a viable hole in appliable codes, I've done two different installs, I'll hold my comments...

You have an answer and are holding out??
Come on, fess up.