[RE-wrenches] METAL ROOF ATTACHMENT

[Bruce Erickson]

Do you know the wind loading vs pull-out resistance of the threads?
This is why I am happy to have the services of a structural engineer, as required by our County for all roof-mounts for the last 4 years or so. At first it was an annoyance to have the extra time and expense of a PE analysis for each job, but now that it's incorporated into our practices, I certainly sleep better during windstorms. We often have to provide more attachments than our seat-of-the-pants approach would have resulted in, but we no longer have liability for it.

I imagine your threaded proposal is based on the lack of access to the underside of the roof for a through-bolted solution. There has been some discussion in the past of toggle type fasteners for this situation. 

Bruce Erickson
Mendocino Solar Service
PO Box 1252
Mendocino, CA 95460
707-937-1701



On Apr 21, 2011, at 2:27 PM, North Texas Renewable Energy Inc wrote:

> Wrenches
>  
> I'm proposing a PV array on a metal building with L feet attached directly thru the roof into the purlins. The plan is to use thread cutting SS bolts, a minimum of ¼-28 pitch. The metal is 14 ga and will engage over 2 full threads and because the array is only 2 landscape modules on NS rails there will be 2 bolts for every module. 36 total. Im using a mag base drill press so the144 holes will be straight & round.
> What surprises can I expect or is there an easier way to go about this. Your 2¢ is welcome.
>  
> Jim Duncan
> North Texas Renewable Energy
> 486 W.N. Woody Road
> Azle Texas 76020
> NABCEP Certified Solar PV
> Installer No.031310-57
> TECL 27398
> ntrei at 1scom.net
> 817.917.0527
> www.ntrei.com
>  
>  
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