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.rat...@valley.net> To: re-wrenches@lists.re-wrenches.org Sent: Tue, April 27, 2010 7:27:08 AM Subject: Re: [RE-wrenches] Lags & TrussesWow, 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 wellbraced 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 theirentire scoop on the project. It may be an overly-cautious approach to liabilityconcerns. If starting from scratch, the truss manufacturer should be able todesign for whatever the application requires. Sistering boards to their trusses might easily freak them out as well. Ask them what they would suggest. There arelots 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@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList 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@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.orgOur 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.rat...@valley.net>richard.l.rat...@valley.net> To: <mailto:re-wrenches@lists.re-wrenches.org>re-wrenches@lists.re-wrenches.orgSent: Tue, April 27, 2010 7:27:08 AM Subject: Re: [RE-wrenches] Lags & TrussesWow, 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 wellbraced 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 theirentire scoop on the project. It may be an overly-cautious approach to liabilityconcerns. If starting from scratch, the truss manufacturer should be able todesign for whatever the application requires. Sistering boards to their trusses might easily freak them out as well. Ask them what they would suggest. There arelots 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 magazineList Address: <mailto:RE-wrenches@lists.re-wrenches.org>RE-wrenches@lists.re-wrenches.orgOptions & settings: <http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList 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@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList 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@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
-- ~~~~~~~~~~~~~~~~~~~ Jeff Clearwater Senior Design Engineer Village Power Design Solar Design Consultation for the Commercial Sector http://www.villagepower.com goso...@villagepower.com Voice: 831-427-2799 Fax: 413-825-0703 245 Dufour St Santa Cruz, CA 95060 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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