[RE-wrenches] Steel roof attachments

[Solarguy]

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 <http://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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