[RE-wrenches] Lags & Trusses

Tue Apr 27 09:52:45 PDT 2010

Our Building Dept requires PE sign-off on all roof-mounts, so our engineer has evaluated a few trusses for us, and has never brought up an issue about lags. I'll ask him what he thinks about this. Most trusses are built all of 2x4's but some we've seen have 2x6 top chords, which are reassuring to see. If you are using something like QuickMounts, which typically use 5/16" lags or hanger bolts, and you have 2x6 material to penetrate, it's harder to imagine it could be an issue, than 3/8" lags into 2x4's. If you're having trusses built for new construction, your could try specifying 2x6 top chords from the truss co.

Bruce Erickson
Mendocino Solar Service
707-937-1701
707-937-1741 fax
PO Box 1252
Mendocino, CA 95460

"Serving the Solar System"

On Apr 27, 2010, at 8:50 AM, Max Balchowsky wrote:

> When we talked to a manufacturer they wanted us to put supporting lumber on top of the roof to support the array rather than penetrate the truss with a lag bolt every 4'. We tried to get them to accept a "drill through" and a bolt with a fender washer. We abandoned the project.....
> 
> Max Balchowsky
> SEE Systems
> 1048 Irvine Ave Suite 217
> Newport Beach Ca. 92660
> 
> 760-403-6810
> 
> 
> 
> ----- Original Message ----
> From: Richard L Ratico <Richard.L.Ratico at VALLEY.NET>
> To: re-wrenches at lists.re-wrenches.org
> Sent: Tue, April 27, 2010 7:27:08 AM
> Subject: Re: [RE-wrenches] Lags & Trusses
> 
> 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
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