[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

Thu May 30 12:12:03 PDT 2024

Scott,

For liability you might want a before and after inspection by a really 
top inspector that you trust.

I would also ask your insurance for guidance. My insurance is always 
telling me that going out of business is the typical last
straw for roofers.

Build a solar pergola😉

Dave Angelini Offgrid Solar
"we go where powerlines don't"
    [2]https://offgridsolar1.com/ [3]  [2]
e-mail  offgridsolar at sti.net
text 209 813 0060

On 2024-05-30 11:41 am, Ray Walters via RE-wrenches wrote:

> 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
>> 
>> www.millersolar.com [1]
>> 
>> CA Lic. 773985
>> 
>> From: RE-wrenches [mailto:re-wrenches-bounces at 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.arey at 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.
>> 
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Links:
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[1] http://www.millersolar.com/
[2] http://members.sti.net/offgridsolar/
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