[RE-wrenches] Mounting system for array on a metal (delta-ribbed) roof

[Bob Clark]

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 at solar-wind.us