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: re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] On Behalf Of Bob Clark
Sent: Thursday, March 12, 2009 11:41 PM
To: re-wrenches@lists.re-wrenches.org
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
bclark@solar-wind.us

--- end of quote ---

