Bob, I agree with Allan re. Tek screws. They are what the steel roofers use.
As concerns your rail spacing relative to the "ribs" in the roof, I think you have a fair amount of flexibility there. Maybe, avoid the ribs altogether by varying the rail spacing accordingly, rather than rigidly adhering to any fixed dimension. Module frames are usually strong enough for you to vary their cantilever, within reason, beyond the rails. Check with the module manufacturer, perhaps, to be sure. Your array will "look good" because your deck of modules will, for the most part, conceal whatever rail spacing lies beneath them, particularly when viewed at any distance. I hope this makes sense. You did a great job with your description, by the way, far less than 1000 words, and good as any picture. Dick Dick Ratico Solarwind Electric Bradford, VT --- You wrote: We did four 6.8 kW systems for a commercial development with standard metal building constructions. This building too had purlins 5' o.c. running parallel to the ridge. After looking into it, we determined that #14 Tek screws worked fine. The blow-mind was something around 1,400 pounds of pull-out strength in the steel we were using (it varies with the gauge of the purlin steel) per screw. (This is from memory and may be off.) We used a single Tek screw per L-foot, with a 2" square of sealing bitumen membrane under each foot, plus caulk after setting the screws. Test your "red" steel for workability. Try to drill holes in an accessible spot. See if this might work for you. Allan Sindelar allan(at)positiveenergysolar.com NABCEP Certified Solar PV Installer Positive Energy, Inc. 3201 Calle Marie Santa Fe NM 87507 505 424-1112 www.positiveenergysolar.com Please consider the environment before printing this e-mail. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bob Clark Sent: Thursday, March 12, 2009 11:41 PM To: [email protected] Subject: [RE-wrenches] Mounting system for array on a metal (delta-ribbed)roof RE-Wrenches: I am certain some of you have dealt with this situation before and can offer some sage advice. Sorry about the long-winded description, but when one is limited to plain text messages, one must use a 1000 (or more) words. SITUATION - Metal building with delta-ribbed roof. "Red" steel (the hard metal kind), C-beam purlins running parallel with the ridge of the roof on 5-foot centers. Unirac mounting system with heavy duty rails running N-S from near the ridge to near the eave across the purlins (this means points of attachment are 5-ft. O.C. along the rails) and solar panels mounted across the rails in landscape mode. The solar panels are 64.6" (1640 mm) long. The array is to be mounted parallel to the roof (non-tilt). It is inevitable that, if the array is to cover as much of the roof as possible (and also look good), that some of the attachments along the rails will fall on the crest of the metal roof ribs while others will fall in the valleys. When we mounted an array on a metal, delta-ribbed roof that was on a wood framed structure, we used Unirac hanger bolts to make the L-feet attachments come out on the same level regardless of whether it was on a rib or in a valley. That way, the weight of the panel would not be resting on the rib (thereby forcing it flat), but on the face of the nut on the upper portion of the hanger bolt. Obviously, we cannot use these hanger bolts that have threads on the bottom for screwing into wood beams. WE CANNOT ACCESS THE UNDERSIDE OF THE ROOF, therefore, bolting the L-feet to the purlins is NOT an option. What can be used that will attach securely, minimize the penetration area of the attachment device (after all, there will probably be 242 points of attachment, which could lead to one leaky roof if not cone correctly), and allow rails to be at the same level regardless of whether the attachment points fall on a rib or in a valley? Furthermore, how can the L-feet be secured to the hardened steel, C-purlins when access to the underside of the roof is not possible? Bob Clark SolarWind Energy Systems, LLC [email protected] --- end of quote --- _______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
