fastener for metal roofing

[MannyBurgos]

What type of fastners is used to secure heavywall conduit straps to the underside of metal roof decking? I will be working on a commercial project which requires mounting heavywall to the underside of the roof. Don't have too much experience with this type of install so your help will be much appreciated.

 

[infinity]

We normally used a self-drilling Tex screw. For RMC you would probably want a #12 or #14 screw in the appropriate length.

 

[MannyBurgos]

We normally used a self-drilling Tex screw. For RMC you would probably want a #12 or #14 screw in the appropriate length.

thank you Infinity. what is the typical length that is used?

 

[infinity]

thank you Infinity. what is the typical length that is used?

Really depends on the thickness of your strap and if you're using a back strap spacer behind the RMC. Rigid straps are pretty thick so I would guess that 1.25-1.5" long should do. You need a screw that's long enough to get past the self-drilling tip and into the threads.

 

[MannyBurgos]

Really depends on the thickness of your strap and if you're using a back strap spacer behind the RMC. Rigid straps are pretty thick so I would guess that 1.25-1.5" long should do. You need a screw that's long enough to get past the self-drilling tip and into the threads.

Thanks Infinity. I appreciate your response.

 

[mgookin]

What type of fastners is used to secure heavywall conduit straps to the underside of metal roof decking? I will be working on a commercial project which requires mounting heavywall to the underside of the roof. Don't have too much experience with this type of install so your help will be much appreciated.

I hope that was mis-stated. You'd never fasten directly to the underside of the roof deck. You'd fasten to the purlins supporting the roof deck.

 

[ActionDave]

I hope that was mis-stated. You'd never fasten directly to the underside of the roof deck. You'd fasten to the purlins supporting the roof deck.

No, right to the deck is common.

 

[GoldDigger]

No, right to the deck is common.

With the end of the screw sticking out on top of the roof?
Is the OP talking about metal roofing or a metal structure with a waterproof element in top?

 

[infinity]

No, right to the deck is common.

I agree, we used to always use EMT in that fashion until the NEC prohibited it a few code cycles ago.

 

[mgookin]

Maybe we're talking about different things.

With a corrugated roof deck which has a few inches or more of iso on top and a hop mopped roof covering above that, I can see a screw penetrating the lower surface of the corrugated deck. Imagine a deck with 1.5"corrugation. The screw never gets to the water barrier.

But with a deck such as a 5-V style where the steel sheet is the roof covering, you would not want to penetrate that with a screw protruding through the water barrier.

 

[MannyBurgos]

This type of roof. Straps to be attached to the lower side of the canals.

 

[mkgrady]

This type of roof. Straps to be attached to the lower side of the canals.

I think the problem is that when the roof gets replaced they will likely screw insulation boards down through the corrugated deck. If you conduit it right where one of the thousands of screws lands it will screw right into your conduit. Kaboom

 

[infinity]

I think the problem is that when the roof gets replaced they will likely screw insulation boards down through the corrugated deck. If you conduit it right where one of the thousands of screws lands it will screw right into your conduit. Kaboom

Just my 2 cents but those roofing screws will probably not go through RMC.

 

[MannyBurgos]

I think the problem is that when the roof gets replaced they will likely screw insulation boards down through the corrugated deck. If you conduit it right where one of the thousands of screws lands it will screw right into your conduit. Kaboom

Sucks to be the roofer at that point. Nec nor does local ahj restrict from such installation. Hence the reason for rmc (2011 code cycle). This is how client wants job so this is how i will do it. All of his existing pipes are attached to underside and they are emt. I just hope he carries an extra pair of clean underwear with em.

 

[masterinbama]

Since I don't see any screws protruding through now, I am guessing this a light weight concrete roof with a ballasted or glued rubber over it.

 

[ptonsparky]

Since I don't see any screws protruding through now, I am guessing this a light weight concrete roof with a ballasted or glued rubber over it.

Don't count on it. New roofs are still going on around here, and I would not bet the farm on those screws not going through RMC if they hit right.

 

[mkgrady]

Don't count on it. New roofs are still going on around here, and I would not bet the farm on those screws not going through RMC if they hit right.

I would expect to find most raceways to be emt. If you hit them just right with a tek screw the screw will go through pretty easy

 

[ActionDave]

I agree, we used to always use EMT in that fashion until the NEC prohibited it a few code cycles ago.

I fondly remember the days when I could stand in a lift and shove a stick after stick of EMT between the roof and the bar joists. With a little jiggle you get out sixty feet before moving the lift.

 

[infinity]

I fondly remember the days when I could stand in a lift and shove a stick after stick of EMT between the roof and the bar joists. With a little jiggle you get out sixty feet before moving the lift.

There are tens of thousands of warehouses and buildings wired that way in EMT with seemingly little problems. :roll: