Securing footing to roof

Frxddy
Frxddy Solar Expert Posts: 113 ✭✭✭✭
I am building feet for my rack system and have a "what does your gut say" question. I had planned on using stainless steel lag bolts to hold the feet down, but then got thinking...... the bolts are under the flashing and will never get wet. I guess they might see some condensation on occasion, but they'd do that stainless or not. I can't imagine zinc plated ones rusting out. I'm wondering if this is a good place to save a hundred bucks? Or, should I pony up the extra money and know they won't corrode at all?

PS... the welded L bracket was just for testing. The real L brackets will be cut from 3/8" angle aluminum. All hardware outside will be stainless.
Feet.jpg 111.2K

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Securing footing to roof

    I can't see big box store zinc plating lasting more than 2 years before you get rust.

    Hot dip galvi is much better, use a washer to keep final torque from clearing the zinc off the underside of the head. Or use stainless that is strong enough. (SS is generally less strong than plain steel)

    But you cant mix steel and alum, you need stainless in there, so may as well use SS bolts !
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Securing footing to roof

    Just me, but I use stainless hardware everywhere, not just on solar projects. It costs more but is worth it in the long run. Customers may not know much about your product but they know you are giving them quality if the hardware is stainless. Why would you ever want to use metal fasteners that rust?
  • mr.radon
    mr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Securing footing to roof

    No reason to go cheap on bolts. Even my fence of 15+ years has SS hardware. (still look like new though the fence doesn't);)

    Plus can you inspect to see what they are going to be doing after 10+ years? nope. just use SS.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Securing footing to roof

    There is one problem with Stainless on Stainless hardware is that the threads can "gall" and lock up.
    Thread galling seems to be the most prevalent with fasteners made of stainless steel, aluminum, titanium, and other alloys which self-generate an oxide surface film for corrosion protection. During fastener tightening, as pressure builds between the contacting and sliding thread surfaces, protective oxides are broken, possibly wiped off, and interface metal high points shear or lock together. This cumulative clogging-shearing-locking action causes increasing adhesion. In the extreme, galling leads to seizing - the actual freezing together of the threads. If tightening is continued, the fastener can be twisted off or its threads ripped out.
    ...
    Lubricating the internal and/or external threads frequently eliminates thread galling. The suggested lubricants should contain substantial amounts of molybdenum disulfide (moly), graphite, mica, or talc. Some proprietary, extreme pressure waxes may also be effective.

    Brass hardware can be much better if these are connections that you need to take apart.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Securing footing to roof

    OK, talked me into it. I will use stainless. Certainly Never Seize should be used on stainless nuts & bolts to help with galling and a torque wrench doesn't hurt a thing. Of course these lag bolts will go in dry as they are going into wood.

    Stainless bolts have about the same strength as #5 steel.

    While we are here.... food for thought... engines have steel bolts in aluminum blocks all over the place. As long as you never have to remove them, no problem!

    I just found this on the internet. Steel is closer to aluminum than stainless!

    Corrosion:
    All metals have a property called nobility. It is a measure of a metal's resistance to corrosion when in contact with another metal. A greater relative difference in nobility between the two metals in contact indicates a greater corrosion potential. Table 1.1.4 ranks the most common metals used in construction in increasing nobility, called the galvanic number.

    Table 1.1.4 - The Nobility of Common Metals

    1. Aluminum
    2. Zinc
    3. Steel
    4. Iron
    5. Stainless Steel - Active
    6. Tin
    7. Lead
    8. Copper
    9. Stainless Steel - Passive
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Securing footing to roof
    Frxddy wrote: »
    I am building feet for my rack system and have a "what does your gut say" question. I had planned on using stainless steel lag bolts to hold the feet down, but then got thinking...... the bolts are under the flashing and will never get wet. I guess they might see some condensation on occasion, but they'd do that stainless or not. I can't imagine zinc plated ones rusting out. I'm wondering if this is a good place to save a hundred bucks? Or, should I pony up the extra money and know they won't corrode at all?

    PS... the welded L bracket was just for testing. The real L brackets will be cut from 3/8" angle aluminum. All hardware outside will be stainless.
    Zinc plating in contact with aluminum might be a problem.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Securing footing to roof

    Assuming the earlier nobility chart is correct, zinc is close to aluminum, so ok for contact.

    The bigger issue is aluminum forms a water proof insulation on the surface within seconds out minutes. You need a cutting washer and should have a anti corrosion paste for good electrical connections.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Securing footing to roof
    BB. wrote: »
    Assuming the earlier nobility chart is correct, zinc is close to aluminum, so ok for contact.

    l
    This site suggests otherwise:http://www.engineersedge.com/galvanic_capatability.htm

    It says for outdoor environments there should not be more than 0.15V difference in the anodic index between dissimilar metals in contact. Zinc plating is at 1.20V or 1.25V, and the highest "flavor" of aluminum is at 0.95V.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Securing footing to roof

    I am just now, in a similar situation as the OP. The system that is shown in the image, appears to be very similar to the UinRac system (altho, the OP is showing some very nice TIG welding, nice scales !).

    I checked into SS Lag screws 5/16 X3.5". $1.74 ea from a quality vendor, Need 100 of em. Expensive, but, the entire system is horrendously expensive.

    To me, if the plating of the lag ever gets tested by water penetrating the flashing shown in the pix, there are very much larger issues than simple corrision of the Zinc plating on the lag. There could easily be water penetration into a rafter, or other significant structual member, and quite possibly some water damage to the interior of the structure ... like dry wall damage and so on. The lags are the ONLY thing that holds the array onto the structure.

    Am not trying to argue with any of the posters. I've decieded to use Zinc plated lags. Will prob use some caulk in the pilot holes, but am relying on the flashing, and its elestomeric bonnet to do its job. These flashings are hidden under panels in my install, but might paint the bonnets with Latex paint.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    Re: Securing footing to roof

    Vic, you might look at galvanized instead of zinc. About the same price, much better protection.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Securing footing to roof

    Hi jburgess,

    Thanks, had considered galvanized. Have gotten some zinc-plated steel jobs. Will prob place some caulk in the pilot holes. Am just hung up on the issue of any water penetrating through the flashing will cause big probs with the rafters and inside the stucture, long before the plating/material will.

    Am notta pro, and this is my first UniRac install. Had thought that Uni would have supplied the lags, but it is a bit application specific, and IMHO a limitation of liability.

    Thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Securing footing to roof

    Just to clarify, galvanized is a very heavy, protective coating of zinc.
    Hot Dipped Galvanized is even heavier.
    Zinc coating is a very thin coating, designed to last long enough to sell the parts with out rust.

    galvanized should be good for 20 years at least, zinc coated, 2 at the most.
    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 ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Securing footing to roof

    Mike,

    To me, galvanized fasteners means that they are Hot-Dipped.

    However, the point that I was trying to make thrice was that the OP shows an ensemble of items, and was asking about fasteners to lag one of them -- the standoff post (foot) -- into rafters. I am with th OP regarding the foot being UNDER A FLASHING, and being exposed to a bit of condensation on occasion. And that if there was a significant water penertation issue over a period of time, that ROTTING the rafter would be a larger concern to me, as well as other water penetration issues -- sheet rock etc. It is my belief a bit of occasional condensation will not harm the ability of the fastener to hold the foot to the rafter.

    That was all that I was trying to say, quite unsuccessfully to this point. The fasteners on hand here, are at least Fastenal, a good brand. The cheesy reatiler's lags, am fairly certain would break, and also usually have shorter thread-lengths.

    Perhaps, I should have speced HDG, and may still, lots of tiem for indecision. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • Frxddy
    Frxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Securing footing to roof

    3 1/2" Stainlesss lags for $.77: http://www.boltdepot.com/product.aspx?cc=9&cm=6&cd=290

    This outfit is "local" to me and treated me well.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Securing footing to roof

    Frxddy,

    Thanks for the link and the info. A vendor had sent that link to boltdepot SS Lags, but was unfamilar with them, and, being in CA, dediced to go with a supplier that has a local outlet, where I could inspect the lags.

    Should order some from BD, and check out the quality.

    Thanks again, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.