<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:12pt">Hey Bruce - <br><br>Engineer's Toolbox lists Asphalt Shingle Roofing at 2.7psf, which seems about right. Further down they also have listings for plywood and OSB, which is often added to structures during a re-roof.<br><br>http://www.engineeringtoolbox.com/roofing-materials-weight-d_1498.html<br><br>The main 'trick' used by Structural P.E.s to allow for "overloading" of roof structural members is to argue that the roof no longer needs the code required 14 psf live load capacity because nobody will be able to walk in the area that the solar panels are installed, so an 11psf live load capacity is more than adequate for safety (14 minus 3 for the solar panels)<br><br>Other than that, it is certainly reasonable and appropriate for the Plan Checker to want to check the load capacity of the roof when weight is being added, and once they are
doing that the most recent span tables are a pretty reasonable place for them to look for guidance. Try the live load argument above and see if that gets you anywhere when you run into this.<br><br>Bruce I had a great time at Solarthon in Castroville this past month - Hope Grid is treating you well!<br><br>Greg McPheeters <img src="http://mail.yimg.com/us.yimg.com/i/mesg/tsmileys2/04.gif"><br><div><br></div><div><br></div> <div style="font-family: arial, helvetica, sans-serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <hr size="1"> <font face="Arial" size="2"> <b><span style="font-weight:bold;">From:</span></b> Bruce Leininger <bruce@gridalternatives.org><br> <b><span style="font-weight: bold;">To:</span></b> RE-wrenches@lists.re-wrenches.org <br> <b><span style="font-weight: bold;">Sent:</span></b> Saturday, July 6, 2013 3:04 PM<br> <b><span
style="font-weight: bold;">Subject:</span></b> [RE-wrenches] Structural Review for Residential PV Systems<br> </font> </div> <div class="y_msg_container"><br><div id="yiv9440274304">
<div>
A local jurisdiction is starting to require that we document
non-truss rafter dimensions, span and attachment points. This seems
to be a fad that other jurisdictions have required at times, and
other times not. When the existing structure was deemed
insufficient, we've either paid a structural engineer to do some
calcs and recommend more attachment points, or sistered the rafters
to match the spacing given in the 20 psf table in the UBC.<br>
<br>
Would the dead load from the PV modules ever be more than that from
adding a second layer of comp roofing, which does not require a
structural analysis? Would the live point loads from the PV system
ever be greater than the point load of a person walking on the
roof? If the answers are "no" and "no", then it seems that a roof
that supports a person walking on it would not be adversely affected
by the installation of a non-ballasted residential PV system.<br>
<br>
I looking for help with the following:<br>
<blockquote>1. Has there been an occasion when a residential PV
system (non-ballasted), that was installed per the manufacturer's
instructions, detached from a roof or caused damage to the
structure of the roof?<br>
2. Is there a good explanation for why structural review for
residential PV systems is necessary?<br>
3. Are there studies or resources that I can present to building
officials to explain why structural review for residential PV
systems is not necessary?<br>
</blockquote>
Thanks for your help.<br>
<br>
Bruce<br>
<br>
</div>
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