Hi Jeff,
Down here in New Zealand corrugated iron is a very common
roofing material. Generally it is mounted on wooden frameworks and we
penetrate the iron with a lag screw which is flashed off. This won't work
for steel purlins like on your job. I have done one install on a steel
framed barn and had to use stainless steel threaded rod instead of lag
screws. I used a captive nut which goes by a number of brand names such as
Nutsert and Rivnut. Basically a large "pop" rivet with an internal thread.
I set these from below and screwed the rod in from the top. I used Loctite
on the thread and also a backnut to lock it into place and ensure it did not
turn when fixing the nuts on the top. The flashings are the small rubber
boots plumbers use and these are fixed with "steeltite" screws and suitable
caulk.
Don't try to use any block that will fit into the corrugations as you will
then end up with a backup of water which will cause corrosion and possibly
seep past your flashing. The rod takes the load directly onto the purlin.
Cheers,
Bruce Geddes
PowerOn
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