I'd hate to speak for the engineers, but usually they do a CYA by saying that the contractor is responsible for assessing whether the structure is adequate, which usually is a satisfactory exclusion accepted by AHJs. Of course that shifts the risk to the contractor.
>From a practical standpoint, you can say the same thing about the truss to header attachment or even the header to wall attachment (especially if not concrete). The truth of the matter is that when a devastating storm hits, all that's left are sticks ( http://www.boston.com/bigpicture/2010/08/remembering_katrina_five_years.html). Local anecdotal evidence from Hurricane Charley suggests that solar panels (mostly solar pool heating) had no impact on whether a roof stays on or not. We saw panels ripped off and we saw completely intact roofs knocked off with panels still attached. I wish we had more pictures, but it was pretty chaotic and that was the last thing on our minds. Given that we make all kinds of other assumptions about existing structures and systems anyway, I am pretty comfortable with the risk/reward tradeoff with a sheathing-only attachment method as long as we have a reasonable analysis from an engineer. Jason On Tue, Jun 3, 2014 at 12:21 PM, Andrew Truitt <[email protected]> wrote: > > All - There have been many products over the years that were engineered to > fasten to roof sheathing only (remember BP Integra and SunPower > SmartMount?), and I can certainly buy that their engineered uplift ratings > are legit in terms of the strength of the connection between the sheathing > and the racking system, but my concern is about the strength of the > connection between the sheathing and the roof framing system. Similar to > using S-5!'s clips, I don't see how we can really trust those footings > without knowing the details (e.g. fastener number and type) of the roof / > rafter connection, and those details can be very tough to access for built > structures. > > I think this has been discussed on this list previously, but I would be > very curious to hear if there have been any new developments in how > designers approach this issue. > > Jason - How do you're engineers handle this challenge in those hurricane > wind zones in Florida, where roofs can fly off even without having a bunch > of sails mounted to them? > > > > For a brighter energy future, > > > Andrew Truitt > > Principal > Truitt Renewable Energy Consulting, LLC > > (202) 486-7507 > > LinkedIn Profile <http://www.linkedin.com/pub/andrew-truitt/8/622/713> > > Company Website <http://truittreconsulting.weebly.com/> > > NABCEP Certified PV Installation Professional ID: 032407-66 > > Colorado Journeyman Electrician License No.: 600132 > > > > On Tue, Jun 3, 2014 at 8:40 AM, Max Balchowsky <[email protected]> wrote: > >> That does look like the early Unirac system, (I don't think they rated it >> for 140 mph). It wasn't designed to "hit" rafters, that's why there six >> screws in each base plate…. >> >> Max Balchowsky >> Design Engineer >> SEE Systems >> 1048 Irvine Ave Suite 217 >> Newport Beach, Ca. 92660 >> 760-403-6810 >> "Building a Better Future For The Next Generation" >> >> ------------------------------ >> *From:* Dave Click <[email protected]> >> *To:* RE-wrenches <[email protected]> >> *Sent:* Tuesday, June 3, 2014 6:06 AM >> *Subject:* [RE-wrenches] Racking System - Identification Help >> >> 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 >> >> > >
_______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
