[RE-wrenches] Steel roof attachments

Mon Oct 22 12:13:32 PDT 2012

In the past, I've used 1/4" SS pop rivets. Two per foot which means you have to drill new holes to either side of the existing hole in the foot. They have a shear strength of about 2500 lbs per rivet.   If this is a parallel to the roof mount, they should work fine. I use Direct Power racks, so I don't know if they are thicker or stronger than the others, but I'm sure they are as good or better. I believe our purlins were 0.62" thick. Certainly some kind of gooey is needed for a seal between the foot and the roof. Lots of different flavors or those, most of them good.
Good Luck, Bob-O

On Oct 21, 2012, at 9:00 AM, Solarguy wrote:

We have had good luck with a drill & tap attachment directly thru the purlins.
I first researched thread pullout strength in steel on the www using 5/16-18 SS bolts. I copped a short section of standard gauge C-purlin from a local steel erection company and did my own simple pullout testing. I don’t have the calculations at hand but I recall that the purlin was .090 thick which allowed almost two full threads in the steel. It was considerably more pullout strength than lags in wood.
We would have used 5/16-24 bolts but fine thread is not available in SS in that small size according to our supplier.  
We rented the smallest magnetic-base drill press available and attached it to a heavy steel plate since the mag wouldn’t stick to the sheet steel roof. The plate has to be large enough to get both feet on to hold it flat which assures that the drilled hole doesn’t wallow out from the drill moving around. I also used a tap guide that assured the tap went in straight and the threads were clean.
Etrna-Bond® tape on the bottom of a Snapnrac L foot attached directly to the roof after clearing metal chips with a can of compressed air. The thick sealant tape made an accurate torque value hard to verify, I ended up just going by feel rather than waiting for the click. We ended up with 2 attachments per 81” rail and 2 landscape modules per pair of rails.
I’m completely confident in the installation and will use it again if the need comes along.
My 2¢ [after 18 years as a machinist and toolmaker] on self-tapping screws for a critical load like this is I would never consider it. The fit will be sloppy and the more oversize or out-of-round your hole the less thread engagement exists. I was disappointed that my bolt supplier could/would not bother to look for the pullout calcs for me but maybe yours will.
The method I describe is labor intensive but it works if done properly.

Jim Duncan
North Texas Renewable Energy Inc
www.ntrei.com
NABCEP PV 031310-57
TECL-27398
ntrei at 1scom.net
817.917.0527

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Chris Mason
Sent: Sunday, October 21, 2012 8:22 AM
To: RE-wrenches
Subject: [RE-wrenches] Steel roof attachments

I have a large steel roof project to install that is giving me some problems. There are many locations so no one is the same.
Most of the roofs are steel sheet over steel purloins with no insulation. The steel sheeting is lying right on top of the purloins. 
Can I use a self drilling self tapping screw to attach? Who makes one large enough?
In some cases I get get to the underneath but working off 30' ladders to make each attachment is too labour intensive as the warehouses are full of goods..

In the case of the roofs that have foam filled panels or corrugated I will have to use EJOT fasteners but these seem overkill for steel on steel fastening, they are very expensive.

Thanks for the help,
-- 
Chris Mason
President, Comet Systems Ltd
www.cometenergysystems.com
Cell: 264.235.5670
Skype: netconcepts

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