PV Solar over Standing Seam Metal Roof fastened with roofing nails

Hi All,

I'm installing 42 panels using S-5! clamps on a large 12/12 standing seam metal roof which was installed using 1 1/4" roofing nails spaced vertically about every 3'.  I'm worried about wind uplift and the entire roof sliding off from the extra downward weight.  Does anyone have experience where a standing seam metal roof that was nailed on failed or came loose under severe wind after a PV array was installed?
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  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    edited September 2016 #2


    Do you have acess to how the roof is constructed structurally?  Can't really do anything without it right? Time to go in the attic! I would thing that the roof should have been screwed on.

    It probably is too late for me to say how much I really hate to see a roof with solar panels on it unless there is no option for ground mounting. I suppose this is a barn with that pitch.
     Offgrid this would be frowned on to weaken the living space roof BTW.  That is my experience.

    12/12 will be really fun ;)  Check with the S5 maker and see what they say.  Good Luck!
    S5.PNG 76.2K
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
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  • jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
    edited September 2016 #3
    So one nail per four square feet?  I tried to rough guess it using nail pullout force, typical uplift force, etc and my GUESS is that you are OK on sliding off (shear) and have a problem with uplift.   Even more so if the clamp isn't right at the nail.  I'd consult a structural engineer who can calculate it properly.

    I am available for custom hardware/firmware development

  • FarlanderFarlander Registered Users Posts: 13 ✭✭
     I have already been in the attic, which is how I know the roof was nailed not screwed.  Structurally the rafters are fine and there would be nothing wrong with installing on this roof but I'm worried that 2 roofing nails every 2' vertically and every 16" into the plywood horizontally may not be suitable to bear the wind uplift.  Sorry for the res you have to really zoom into see the nails.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    I would be also!  Check with S5 and see what they say. That will cheapest.  Then, I would do what jonr said and hire an engineer.

    If this had to be done, I would use rails into the studs which is going to defeat the water tighness of the standing seam and would be a major pain, but it would not uplift !

    The last thing I can think of here would be to some how gain acess to hammer bend all those nails in and beyond the solar foot print.

    What is wrong with a ground mount?

    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • FarlanderFarlander Registered Users Posts: 13 ✭✭
    Bending the nails over is actually the smartest suggestion I've gotten so far.  I was hoping for some kind of self tapping nut that could be threaded onto the nail shank... no luck yet.

    Dave, the ground mounts are a terrible pain in the butt and way more expensive.  Not using the roof when it's available and has good exposure is loco in my opinion, off grid or otherwise.

    I do have an engineer, just trying to avoid the painful realization that this may not fly.
  • jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
    edited September 2016 #7
    Similar would be a  push-on retainer nut or "push-nut for unthreaded shaft".  The thin spring steel washer like things that push on and are then very hard to get off.

    Maybe a greater air gap from panel to roof  and panel to panel helps reduce uplift.  Avoid panels near the corners and edges of the roof.

    I am available for custom hardware/firmware development

  • PhotowhitPhotowhit Solar Expert Posts: 4,912 ✭✭✭✭
    Not sure why you would say;
    • Dave, the ground mounts are a terrible pain in the butt and way more expensive.  Not using the roof when it's available and has good exposure is loco in my opinion, off grid or otherwise.

    Can you imagine trying to trouble shoot the array on a 12:12?
    You have no chance of problems with roof leaks.

    I can see such a large array 42 panels, as having some issues maintaining a low profile, but I can see advantages, and set mine up that way.  Knot 2 loco yet, maybe tomorrow...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • PhotowhitPhotowhit Solar Expert Posts: 4,912 ✭✭✭✭
    Not sure why you would say;
    • Dave, the ground mounts are a terrible pain in the butt and way more expensive.  Not using the roof when it's available and has good exposure is loco in my opinion, off grid or otherwise.

    Can you imagine trying to trouble shoot the array on a 12:12?
    You have no chance of problems with roof leaks.

    I can see such a large array 42 panels, as having some issues maintaining a low profile, but I can see advantages, and set mine up that way.  Knot 2 loco yet, maybe tomorrow...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    edited September 2016 #10
    Maybe me also, loco manyana Photowhit.
     We have alot of Solar companies installing up here in our rural county.  They always said the same thing about how hard a ground mount system was and how expensive. I taught three of them how to do a 1.5" pipe mount when the owners told the solar companies  "on the ground or get lost". Kind of crazy to risk an excellent roof on 5+ acres of land.

    But there are plenty of people who will install low quality. They just change their business name every 5 years and warrany issues are over. :'(  The roof here should have been screwed down, so corners are already cut on this solar idea in my opinion.

    At lease the OP is asking!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • FarlanderFarlander Registered Users Posts: 13 ✭✭
    edited September 2016 #11
    I see the advantages and disadvantages of roof mount and ground mount, but as far as troubleshooting we always use microinverter or power optimizers to be able to easily identify a problem panel should one exist.  A little more careful observation shows 2 nails every 2' x 16", anyone care to try to crunch the math on this?
  • Mountain DonMountain Don Solar Expert Posts: 494 ✭✭✭
    If the installation of the pv panels on top of the standing seam roof means perforating the metal for the pv mounts you will have obviated one of the wonderful things about standing seam. To my mind the primary reason to have a standing seam roof is the fact of not having perforations. That's without saying anything about the negatives of the system having been nailed on. No uplift resistance of any kind that counts.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • mike95490mike95490 Solar Expert Posts: 8,288 ✭✭✭✭✭
    Farlander said:
    Bending the nails over is actually the smartest suggestion I've gotten so far.  I was hoping for some kind of self tapping nut that could be threaded onto the nail shank... no luck yet.....

    Called Speed Nuts
    http://www.mcmaster.com/#speed-nuts/=1425ur2

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
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  • Ralph DayRalph Day Solar Expert Posts: 886 ✭✭✭✭
    If the nails are iffy on the number per square foot, how about installing proper roofing screws in between the nail spacings.  Or pulling the nails and replacing with roofing screws.  Saw that done on a barn roof where the nails would pull part way out in wind storms, then just get hammered back down...to do over again.  Pulled and replaced with screws solved the problem.

    Ralph
  • AnawaAnawa Solar Expert Posts: 211 ✭✭✭
    If the deck is 3/4" (which it appears given the length of the protruded nail through the deck) and the nailing pattern is 16" X 24", then it would suggest the SS roof panel was installed according to the manufacturers installation instructions. Here is a link to at least one manufacturer that instructs the 16" X 24" nailing pattern:  http://www.bestbuymetals.com/pdf/standing-seam-installation-guide.pdf

    I would suggest that you contact s5, provide them with your as-built information and ask if installing their product per their instructions on this substrate is what they will warrant. I think DA suggested this in a prior post.

    Just saying.

    Paul
    in Georgia
    Paul 
    in Georgia

    System 1: PV- 410w Evergreen, Mppt- Blue Sky Solar Boost, Batt - 225ah Deka AGM, 12v led house lighting,
    System 2: PV- 215w Kyocera, PWM - Morningstar PS30, Batt- 225ah Deka GC's, 12v led house lighting, Dankoff 12v water pump,
    System 3: PV- 1.5kw Kyocera, Grundfos 11 SQF well pump, 3000 gal above ground water storage, dom water & irrigation,
    System 4: PV- 6.1kw Kyocera, Mppt- Outback FM80-2ea, Inverter- Outback FX3648-2ea, Batt- 804ah GB traction, Grundfos BMQE booster pump 240v, Mitsibushi mini-splits 240v, 18k and 15k
  • AnawaAnawa Solar Expert Posts: 211 ✭✭✭
    FWIW, I think the concern for s5 with will come down to nails vs. screws in the SS roof panel installation and not the fastener spacing.

    Paul
    in Georgia
    Paul 
    in Georgia

    System 1: PV- 410w Evergreen, Mppt- Blue Sky Solar Boost, Batt - 225ah Deka AGM, 12v led house lighting,
    System 2: PV- 215w Kyocera, PWM - Morningstar PS30, Batt- 225ah Deka GC's, 12v led house lighting, Dankoff 12v water pump,
    System 3: PV- 1.5kw Kyocera, Grundfos 11 SQF well pump, 3000 gal above ground water storage, dom water & irrigation,
    System 4: PV- 6.1kw Kyocera, Mppt- Outback FM80-2ea, Inverter- Outback FX3648-2ea, Batt- 804ah GB traction, Grundfos BMQE booster pump 240v, Mitsibushi mini-splits 240v, 18k and 15k
  • FarlanderFarlander Registered Users Posts: 13 ✭✭
    Thanks everyone for commenting - Obviously it is preferred not to penetrate the metal roof at all, which is how this job was sold, and obviously a seamed metal roof has no exposed fasteners so you cannot simply remove nails and replace them with screws, the fasteners are underneath the roof itself.  The only way to reinforce the roof are bend over the nails or attach something to the back of them, OR, screw through the surface of previously unbroken roof and I don't like that idea very much either.  The S-5 clamps do not penetrate the roof, they simply clamp onto the standing seam, the only question is whether the whole thing blows away like a kite at 70mph because the roof was not fastened securely enough.  The clamp strength is not the issue, they can withstand like 700psf uplift force or something crazy.  Still looking for input from other pros who have done work on similar situations.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    You could remove the roof to get to the fasteners as was suggested but if there is ground space why? The picture below is another reason that I ground mount. A couple hours later in this photo the sun came out and filled the battery tracking the winter sun.


    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
    edited September 2016 #19
    I've seen nothing that indicates that the panels will see a larger uplift force than the metal roofing.   So there might be the argument that the roofing meets specs and has stayed on, so the panels will too.

    I am available for custom hardware/firmware development

  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    Well then sign it off for him Jon :)   I have seen the S5 on roofs and depending on the height that he chooses or has to use,
     there could be wind under the array that will add to the uplift!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • jonrjonr Solar Expert Posts: 1,266 ✭✭✭✭
    edited September 2016 #21
    :-).  My understanding is that if you can get some (6"?) airflow around/under the panels, then the uplift force goes down (the pressure on both sides of the panel can equalize).   It's the flow over the roof acting as an airfoil that causes the lift - not wind getting under anything.    But such advice is probably worth less than you paid for it.....

    One of the key CFD result from this investigation was that the panels should be mounted such that air can flow under the panels. It was determined that the uplift on the panels can increase by a factor of 3x if the panel are blocked to prevent air from flowing underneath.

    http://http//www.predictiveengineering.com/consulting/cfd/parametric-cfd-wind-force-analysis-residential-roof-mounted-photovoltaic-panel

    I am available for custom hardware/firmware development

  • WaterWheelWaterWheel Registered Users Posts: 325 ✭✭✭
    If you're comfortable playing on a 12/12 roof then why not just buy a few boxes of metal roofing screws and add some screws to the roof.      They're self drilling and pop right in.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • MarkCMarkC Solar Expert Posts: 175 ✭✭✭
    I've used what is termed "Z" foots with three lag screws on a (cheap) metal building roof that lag into the roof rafters.  These have a sticky compression gasket on the bottoms that seal the footings to the metal roof.  I beefed up the roof rafters/studs with a parallel set (and hurricane tie downs) before installation of the panels.  I has worked well for over 2 years now with no signs of pull out or leaks.  Installing a second array using the same system.  

    It does raise the panels up an additional couple of inches - but maybe not much over the "S5s"?

    Of course, these footings help hold the thin roof panels down to the roof structure so that the real worry is your roof design for lift.   As we have hurricanes, this is a real concern for us.  I can just see my metal building floating over my cabin!!
    3850 watts - 14 - 275SW SolarWorld Panels, 4000 TL-US SMA Sunny Boy Grid tied inverter.  2760 Watts - 8 - 345XL Solar World Panels, 3000 TL-US SMA Sunny Boy GT inverter.   3000 watts SMA/SPS power.  PV "switchable" to MidNite Classic 250ks based charging of Golf cart + spare battery array of 8 - 155 AH 12V Trojans with an  APC SMT3000 - 48 volt DC=>120 Volt AC inverter for emergency off-grid.   Also, "PriUPS" backup generator with APC SURT6000/SURT003  => 192 volt DC/240 volt split phase AC inverter.  
  • PhotowhitPhotowhit Solar Expert Posts: 4,912 ✭✭✭✭
    One of the advantages of a Standing seam roof is that it has no exposed nails or screws, I'm sure the OP would rather not negate this advantage, If possible.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,486 ✭✭✭✭✭
    MarkC said:
    I've used what is termed "Z" foots with three lag screws on a (cheap) metal building roof that lag into the roof rafters.  These have a sticky compression gasket on the bottoms that seal the footings to the metal roof.  I beefed up the roof rafters/studs with a parallel set (and hurricane tie downs) before installation of the panels.  I has worked well for over 2 years now with no signs of pull out or leaks.  Installing a second array using the same system.  

    It does raise the panels up an additional couple of inches - but maybe not much over the "S5s"?

    Of course, these footings help hold the thin roof panels down to the roof structure so that the real worry is your roof design for lift.   As we have hurricanes, this is a real concern for us.  I can just see my metal building floating over my cabin!!
    That is the problem here that the roof design was flawed for solar by using roofing nails that are designed to be fully driven into wood framing. People who use OSB or Plywood under the roof must use a screw with a rubber tipped washer for expansion.  
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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