[RE-wrenches] Lags & Trusses
Jeff Clearwater
jeffc at villagepower.com
Tue Apr 27 12:28:22 PDT 2010
Hi Drake and all,
We have had both engineers and inspectors question the use of a 3/8"
4" lag in a 2x4 top chord and I think rightfully so. When we have a
chance to spec new construction we have the architect replace the 2x4
top chord with a 2x6.
And when we have to go into 2x4's we either shorten our lag to a
5/16" 3.5" or even 3" (if we can get away with it on the uplift
calcs) so we stay in the top half of the wood fibers on the truss.
We have also sistered or blocked 2x4s when there was concern.
But like Bruce said - I cannot imagine there ever being a problem
with a 2x6 with a 4 " lag (only 3.5" of which goes into the wood)
unless you were using 1/2" lags!
The real issue is in installation. Installing a lag so that it
glances the side and splits the rafter or hitting a knot and not
backing off could cause problems. So we are really careful in
installation to make sure we are right on the center of the truss -
we drill tiny probes everytime - that's where the real issue is -
once engineering is happy of course.
Hope that helps!
Jeff Clearwater
Village Power Design
>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
>> Office - 740-448-7328
>> Mobile - 740-856-9648 _______________________________________________
>> List sponsored by Home Power magazine
>> --- end of quote ---
>> _______________________________________________
>> List sponsored by Home Power magazine
>>
>> List Address: RE-wrenches at lists.re-wrenches.org
>>
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>
>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
>><<mailto:Richard.L.Ratico at VALLEY.NET>Richard.L.Ratico at VALLEY.NET>
>>To:
>><mailto:re-wrenches at lists.re-wrenches.org>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
>>Office - 740-448-7328
>>Mobile - 740-856-9648 _______________________________________________
>>List sponsored by Home Power magazine
>>--- end of quote ---
>>_______________________________________________
>>List sponsored by Home Power magazine
>>
>>List Address:
>><mailto:RE-wrenches at lists.re-wrenches.org>RE-wrenches at lists.re-wrenches.org
>>
>>Options & settings:
>><http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>>
>>List-Archive:
>>http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>>
>>List rules & etiquette:
>>www.re-wrenches.org/etiquette.htm
>>
>>Check out participant bios:
>>www.members.re-wrenches.org
>>_______________________________________________
>>List sponsored by Home Power magazine
>>
>>List Address: RE-wrenches at lists.re-wrenches.org
>>
>>Options & settings:
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>>
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>>
>>List rules & etiquette:
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>>
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>>
>
>
>_______________________________________________
>List sponsored by Home Power magazine
>
>List Address: RE-wrenches at lists.re-wrenches.org
>
>Options & settings:
>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
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--
~~~~~~~~~~~~~~~~~~~
Jeff Clearwater
Senior Design Engineer
Village Power Design
Solar Design Consultation for the Commercial Sector
http://www.villagepower.com
gosolar at villagepower.com
Voice: 831-427-2799
Fax: 413-825-0703
245 Dufour St
Santa Cruz, CA 95060
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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