Great, thoughtful answers from all. I’m going to push this to the FineHomeBuilding podcast crew for their ideas, too.
I hate to ask the question I might not want to hear the answer to, but I can’t think of anything more horrible than a failed rafter. That would be the resi equivalent of the infamous Bakersfield fire. Thanks, Scot From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> On Behalf Of Ray Walters via RE-wrenches Sent: Thursday, May 30, 2024 1:42 PM To: re-wrenches@lists.re-wrenches.org Cc: Ray Walters <r...@solarray.com> Subject: Re: [RE-wrenches] How many times can a rafter have a lag screw put in and out before it is no longer structurally sound? Some roofs getting their 3rd set of new shingles I would add to this that the size of the lag is a factor too. 3/8" lags into 1-1/2" wide rafters are going to cause much more damage, and leave larger voids, than the new 1/4" high strength lags I use now. I like the rafter sistering idea, as a solution, as well as moving the rails up or down several inches to get away from the previous hole. A third idea is staggering the mount pattern from rail to rail, which is something we should all be doing anyway to insure the loads are more equally distributed across all the rafters. Then we just change the pattern on the 2nd installation. Unfortunately I think much of this will be lost, since some of the companies that roofers subcontract with to do these remove and replace jobs are not always the top solar contractors. Ray Walters Remote Solar On 5/29/2024 10:17 PM, William Miller via RE-wrenches wrote: Scot: Fascinating question. It’s a bit ironic that the changing climate is damaging the equipment we are utilizing to combat climate change. A lag unscrewed will damage a wooden member less than a lag ripped out. >From your post it seems we are dealing with the former, rather than the latter. If your layout isn’t changing there is a likelihood that the new mounting locations will be at our near the old mounting locations. This will be true for a rafter lag or deck mount screw. It seems to me the process of re-screwing in the same spot in a rafter is just as questionable as re-screwing in the same spot in sheeting. I see no benefit in deck mounting and many disadvantages. If severe weather is an issue I would avoid deck mounting unless you have vetted the decking and the applicability of the chosen fasteners to that material. I would not standing-seam mount without knowing how the sheeting panels are secured and finding a method to calculate how many clips are needed given the increasing wind loads. I see two questions about reinstalling screws repeatedly: 1. Is the rafter less able to support loads? Or, 2. Is the rafter (or decking) less able to retain the fasteners holding the PV to the roof? Speculation on the above: 1. Wood fibers adhere to each other. They are not like a bundle of straws. If you damage a fiber in one place, it is supported on either side of the point of damage by this adherence. My guess is by just withdrawing screws a few times you do not compromise the load handling ability of a rafter member. Site built rafters require different considerations than trusses. Site built are a wild-card and need to be considered on a case-by-case basis. 2. If you penetrate wood with screws multiple times in a small area, you are going to make that area “soft.” Screw holding capabilities will be drastically reduced. Options that I see: 1. Flashed stanchions. The lags never need to be removed. 2. Blocking, to attach in new locations. 3. Sistering, again to attach in new locations. 4. Not deck mounting (IMHO). Anecdote: We had a tile roof mount inspected one August afternoon. The inspector insisted on looking in the attic. We asked why and he said this city has a particular concern about structural integrity of wood framed roofs. I was aware of this because I have had some silly arguments about this with the lead inspector. Apparently they have seen a lot of big-box solar company installers drive lags carelessly and had the lags blow out the side of the rafter. If they spot this they make the installer hire an engineer and design a system to sister the rafters to engineering standards. I totally get this concern. We use a rafter locator and are really careful. This is not to say we have not had a blow out now and then. You gotta have a feel for the torque resistance of a lag while seating. Thank you for bringing this up. As I said, fascinating (to this wonk). William Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 <http://www.millersolar.com/> www.millersolar.com CA Lic. 773985 From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org <mailto:re-wrenches-boun...@lists.re-wrenches.org> ] On Behalf Of Scot Arey via RE-wrenches Sent: Wednesday, May 29, 2024 3:16 PM To: 'RE-wrenches' Cc: scot.a...@solarcentex.com <mailto:scot.a...@solarcentex.com> Subject: [RE-wrenches] How many times can a rafter have a lag screw put in and out before it is no longer structurally sound? Some roofs getting their 3rd set of new shingles With all our Texas hail storms, we now have roof solar systems that might have to come down for the third time as hail-pockmarked shingles need replacement. We’re at the 11-year mark of doing business and we have some customers ready for another insurance roof claim, So that means a new set of lag screws drilled into rafters…after how many times is that 2x6 rafter not 2x6 strength? I’ve asked this to my 3rd party structural engineer and instead of an answer got a “wow, hadn’t thought of that.” We’ve considered going to deck mounts to avoid rafters at the 3rd “detach and reset.” Any of you guys consider this and have your techniques? I suppose in perfect world, the mount would stay in place and roofer would shingle around it but we still use old-school metal flashing so that is really not possible. I look forward to hearing your thoughts on this. _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org <mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. 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