Jason, thanks for the comment! I agree that systems could connect to
just sheathing and stay on the roof- I think Zilla has a product that
does this too. My concern about wind resistance stems from the fact that
there appeared to be an engineer's stamp on the Unirac calcs with lag
screws and then something completely different was installed in the
field. It's likely that this installer has used this same mounting
system in windier coastal areas so hopefully their fastener selection
had some informed analysis... I didn't see any, though.
And to be clear, I'm not looking to overrule another PE if it is in fact
an engineered system and it's just that the wrong set of plans got
submitted to the building department.
DKC
On 2014/6/3, 10:12, Jason Szumlanski wrote:
Dave,
I can't identify your hardware, but I just wanted to comment on your
comment about hitting rafters. There are products out there that can
obtain the requisite load ratings without connecting directly to
structural members. We have had systems engineered and permitted using
Ecofasten products on low-slope roofs that fasten only to wood
sheathing or metal roof materials in 170 mph zones in Florida (ASCE
7-10, FBC 2010). I'm not an engineer, but I've been told if there is
adequate data on pull-out and shear, you can use that data to properly
design a system without hitting rafters with the right number of
attachment points. I don't like the looks of what you pictured, but
it's plausible that it was an engineered system design. The permit
drawings not matching... that is another story...
If, for example, each of the six fasteners provide 100 pounds of
pullout strength with a safety factor, that would be good for 12 sq ft
at 50 spf uplift per attachment. 250 fasteners would be good for about
5kW of solar.
Jason Szumlanski
Fafco Solar
On Tue, Jun 3, 2014 at 9:06 AM, Dave Click <davecl...@fsec.ucf.edu
<mailto:davecl...@fsec.ucf.edu>> wrote:
Hi all,
Anyone know what this racking system is? The permit drawings say
Unirac with lag screws and Eco-Fasten flashings, which this pretty
clearly isn't. I'd never seen this before, and I imagine this wind
resistance is not quite the 140 mph that the installer claims it
is. Of the ~250 wood screws holding this system down into the
roof, I think six of them accidentally hit rafters.
Thanks!
Dave
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