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 offgridso...@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-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
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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