Wow, this could be a hairball. Needless to say, we've all probably already done
this, more than a few times. But....as a former carpenter.... though claiming no
expert truss knowledge, my sense is that the top chord of the trusses should be
in compression. Therefore, a 3/8" diameter lag, for instance, would substitute
steel for wood in compression, not a bad move. The trusses should be very well
braced laterally by the roof deck. I don't see the problem.

Is the new roofing material being applied over existing roofing, applying
additional load? Are there circumstances that make this a special truss
application, cantilevers, slate roofing, etc.?

It would be interesting to talk directly with the manufacturer, to get their
entire scoop on the project. It may be an overly-cautious approach to liability
concerns. If starting from scratch, the truss manufacturer should be able to
design for whatever the application requires. Sistering boards to their trusses
might easily freak them out as well. Ask them what they would suggest. There are
lots of truss manufacturers if this one can't handle the job. 

Dick Ratico
Solarwind Electric


--- You wrote:
Hello Wrenches,

I just talked to a carpenter, who we are installing an array for.  He 
is putting a new roof on the building and was talking to the 
manufacturer of the trusses.  He mentioned that he was having an 
array installed on the roof.

The truss manufacturer said there were problems with weakening the 
truss structure with the lag screw penetrations.  We are now planning 
to sister boards next to his trusses instead of penetrating them.

Does this seem like a potential issue?  Is there any data on this?

Thanks,

Drake


Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
NABCEP TM  Certified PV Installer
Office - 740-448-7328
Mobile - 740-856-9648  _______________________________________________
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