mounting panels to treated-wood frame

[J.P.M.]

Yes, you've made that pretty clear; thanks for your opinion.


I believe one factor in the dominance of all metal tinker-toy type racking systems is the ease of assembly. Installers want to get the systems up quickly and homeowners appear willing to paymuch higher costs than what I'm aiming for. In my case, I'm trying to minimize cost and don't mind a little more thinking and assembly work.

You're welcome. It's offered for what use, if any, others besides you may have for it.

While there may be something to the logic in your tinker toy analogy, sometimes folks consider only first cost and not long term costs, including the cost of increased maintenance/repair/servicing, and/or they put little or no value on their labor or sweat equity.

NOMB or concern, but it reads (to me only perhaps) that you're aiming for lowest initial costs. Different strokes.

[RShackleford]

Since, among other things, this is a place to express opinions, for array framing and structural materials, mine is that there are usually materials other than wood that are more suitable and better fit for purpose for PV array racking and structural support material.

Yes, you've made that pretty clear; thanks for your opinion.

Also, from looking around at the dearth of wood in PV arrays, both residential and commercial, I'd hazard a guess and suggest that there's a pretty high probability a lot of other folks who design and build arrays for a living might agree with that opinion.

I believe one factor in the dominance of all metal tinker-toy type racking systems is the ease of assembly. Installers want to get the systems up quickly and homeowners appear willing to paymuch higher costs than what I'm aiming for. In my case, I'm trying to minimize cost and don't mind a little more thinking and assembly work.

[RShackleford]

I think the 2x8s may be such an integral part of the engineering design that it may require PE to recalculate if you eliminate them. That may be more expensive than leaving the 2x8s and relying on the Iron Ridge drawings to place the rails on your previously engineered wood structure.

You may be right; not quite sure how to approach the AHJ about this. Leaving the 2x8s in place should not be particularly expensive, it's about $100 worth of lumber. If I do leave 2x8s in place, I can look at some of the cheaper rails (like ProSolar or IronRidge XR10 or XR100) that require supports more than every 8ft.

[J.P.M.]

Isn't that the point of buidling codes ? Make-work for tradesmen and others ? You might be familiar with NEC 404.2(c) ? No, I'm being cynical. I think the main point of this hoop is the bldg inspectors covering their asses if the installation self-destructs.

Anyhow, I'm quite clear that you do not approve of using wood for the frame and that you think my PE's work is incomplete.

Nationally and internationally recognized codes, and also lots of local design codes that often have the force of law behind them have several objectives. One such big objective is to help ensure, to the greatest extent possible and practical, safe design for the benefit of the public good.

However, I sure do appreciate the reality that inspectors and code compliance can make life less than a cake walk. I'd note too, that I usually don't think that if I'm the customer and having work done that requires inspection(s) or some code compliance.

One reality, among many, is that whatever the intended purpose(s) of design codes, without them, most inspectors wouldn't have a job. Take that FWIW, cynical or not or anything/everything in between.

I've dealt with inspectors of all sorts through an entire engineering career. Most take their responsibility very seriously and want to do the best they can to ensure code conformance - not usually as an end in itself, but as a way to help ensure public safety if for no other reason (and this is the cynical part) than their own job security.

More FWIW, and a corollary to the fact that none of us is as smart as all of us, a good inspector can improve on a design and some can be very valuable sources of information and real help. There's not too much an experienced and seasoned inspector hasn't seen. A good portion of the time, at least to my experience, usually things I haven't learned (yet). More cynicism: It never hurts to grease an inspector's pole 1X/a while if it's warranted. Everyone likes recognition.

To your question: I'm not as familiar with the NEC as some other codes, but 404.2(c) that deals with switches that control lighting loads seems, in and of itself, pretty straightforward.

However, and taking a larger view of the need/usefulness/purpose of design codes, my code experience (that is, dealing with lots of different codes: U.S., other countries' codes, and international codes) has taught me, among other things, that reading a code section in isolation, and so perhaps out of context and without knowing and understanding, or at least being mindful of how it may impact other, perhaps far flung sections of the same code and vice versa, or how any section of any code may impact other seemingly unrelated codes, can lead to problems.

As for what I may think of wood as a construction material for most any flat plate solar application, based on my training, education and experience for what any of that may be worth, including what I think I may know about structural engineering and also about PV arrays, I am of the opinion wood is not usually the first and often not best choice for a design of a PV array support system for several reasons.

But, opinions vary and mine is but one.

I'm more than willing to listen/consider contrary opinions about that - that's one way I learn stuff. But in general saying I'm wrong about some point simply because someone may not like what I think, or because it might not fit their preconceived view of reality, or they may feel/fear it will cause them to reexamine their opinion or that they may have made a mistake or messed up because of ignorance will not, in/of itself change my mind.

Besides, unless there's a glaring error, it's not for me to approve or disapprove of design choices made my licensed professionals, including material choices. It ain't my design, and I sure as hell won't pass judgement on what some other engineer did, particularly based on the little information I have at this time.

To me, that would be an irresponsible breach of professional ethics in ways Ampster seems to not get - but then, he's not a P.E. so he doesn't need to concern himself with things.

As a general observation, if a PV array support structure was made of wood, I'd probably not stand next to it in a windstorm after it had been in place for a few years, and I sure as hell wouldn't want the increased maintenance associated with wood.

Since, among other things, this is a place to express opinions, for array framing and structural materials, mine is that there are usually materials other than wood that are more suitable and better fit for purpose for PV array racking and structural support material.

Also, from looking around at the dearth of wood in PV arrays, both residential and commercial, I'd hazard a guess and suggest that there's a pretty high probability a lot of other folks who design and build arrays for a living might agree with that opinion.



Take what you want of the above. Scrap the rest.

[Ampster]

........

If running rails perpendicular to 2x12s and eliminating the 2x8s, those angle brackets should work well. Two issues though: Need to attach the angle to the top of the 2x12 beams at a 25-degree slant (so parallel to the rails), and might want to just use generic angle iron, since the IronRidge parts are $10+ and I'd just be discarding the u-bolt.

One leg of the angle brackets that I used was long enough so that the rail would clear the 2x12 if mounted on the downhill side of the double 2x12s.

If attaching the IR rails to the 2x8s, I need to do it so possible warpage of the 2x8s does not simply bend the rails and defeat the purpose.

If you look at the details your PE provided, those 2x8s are blocked in 3 places so that means they won't twist and will stay parallel. The only other dimension they can warp is to bow across the thickest cross section. If you pick boards with straight grain and small tight knots you should not have any serious issue with warping. The blocking makes the whole 2x8 section work as a system. Even the diagonal brace across the bottom adds structural integrity.

I really need to answer two questions:

1. Can I make an all-wood frame (no IR parts at all) stiff enough that warpage won't be a problem ? (You say you've seen plenty of wooden ground-mount systems; did they not use rails at all ? Your's apparently did use rails, even though you didn't attach the panels to them).

Your PE has done a good job of engineering that structure based on what I have seen during my 65 years working on and around wood frame construction. Most of the wooden ground mount systems I have seen did use rails of some sort. You can see the aluminum in @bcroe's pictures. I did also did attach my panels to the rails as explained earlier. Otherwise there would have been no reason to install the rails in the first place.

2. If answer to #1 is no, can I convince the AHJ to let me replace the 2x8s with IR rails (paying attention to the issue of diagonal bracing with all or most of the 2x8s eliminated).

I think the 2x8s may be such an integral part of the engineering design that it may require PE to recalculate if you eliminate them. That may be more expensive than leaving the 2x8s and relying on the Iron Ridge drawings to place the rails on your previously engineered wood structure. Every building department is unique and you may get lucky.

[RShackleford]

I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I have uploaded a picture to llustrate.. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.

Oh, now I see; you clamped it, but on the flange on the backside where the holes for thru-bolts are located.

[Ampster]

I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?

I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I have uploaded a picture to llustrate.. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.

I will try to answer your other questions later.

[Ampster]

I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?

I am not recommending that approach but for me it was the most practical way since I had easier access from below my patio cover than from above. I will try to upload a picture. I am still looking for a bracket like I have seen on parking lot arrays. Those are all fastened from below.

[RShackleford]

I used the angle brackets that Iron Ridge sells. I also agree with you that it makes attaching and adjusting the panels much easier. I mentioned earlier that I used fender washers to attach my panels. What I did not make clear was I attached them from below the panels using the flanges on the panel frames. This was easier because it was much quicker to access the panels from below. However since there were 4 bolts for every panel I used a little more hardware.

I'm still a little confused about your system. You attached the panels to your IronRidge rails, but you used fender washers instead of UFOs ?

I couldn't find any prefabricated brackets although I have seen them on parking structure mounted panels.

I believe I've dropped the notion of using fender washers; I'm thinking of using: https://www.solarflexion.com/product-p/c225imc-24.htm (or possibly a similar Unirac product) along with SS lag bolts.

As far as attaching the rails to the 2x8s tThere is a convenient slot in the side of the rails that takes the head of a bolt that then goes through the angle bracket. No issue if you are running the rails perpendicular to the 2x8s. If you are running the rails parallel, then you have to attach the angle brackets to the 2x8s with lag bolts and then mount the rail to the inside of the angle bracket so the rail is roughly centered over the 2x8. In the case of the 2x12s the first explanation should also work if I understand your question correctly.

I definitely won't run rails perpendicular to 2x8s - I'm committed to landscape mode, and though I could clamp to the short sides of the panels, than would require 20+ft rails instead of 14ft (which are expensive enough).

If running rails perpendicular to 2x12s and eliminating the 2x8s, those angle brackets should work well. Two issues though: Need to attach the angle to the top of the 2x12 beams at a 25-degree slant (so parallel to the rails), and might want to just use generic angle iron, since the IronRidge parts are $10+ and I'd just be discarding the u-bolt.

If attaching the IR rails to the 2x8s, I need to do it so possible warpage of the 2x8s does not simply bend the rails and defeat the purpose.

I really need to answer two questions:

1. Can I make an all-wood frame (no IR parts at all) stiff enough that warpage won't be a problem ? (You say you've seen plenty of wooden ground-mount systems; did they not use rails at all ? Your's apparently did use rails, even though you didn't attach the panels to them).

2. If answer to #1 is no, can I convince the AHJ to let me replace the 2x8s with IR rails (paying attention to the issue of diagonal bracing with all or most of the 2x8s eliminated).

[Ampster]

.......Good point. My purpose for using the IR rails is twofold: to mitigate the wood-warpage problem, and to make the panel mounting easy (with their UFO bolts). Certainly any grade of rails accomplishes the latter. I'd have to ponder how to attach the rails to the 2x8s so warpage of the wood doesn't bend the rails. And if I'm able to delete (all but two of) the 2x8s and use XR1000, I need to figure how to attach the XR1000s to the twin 2x12s.

I used the angle brackets that Iron Ridge sells. I also agree with you that it makes attaching and adjusting the panels much easier. I mentioned earlier that I used fender washers to attach my panels. What I did not make clear was I attached them from below the panels using the flanges on the panel frames. This was easier because it was much quicker to access the panels from below. However since there were 4 bolts for every panel I used a little more hardware. I couldn't find any prefabricated brackets although I have seen them on parking structure mounted panels.

As far as attaching the rails to the 2x8s tThere is a convenient slot in the side of the rails that takes the head of a bolt that then goes through the angle bracket. No issue if you are running the rails perpendicular to the 2x8s. If you are running the rails parallel, then you have to attach the angle brackets to the 2x8s with lag bolts and then mount the rail to the inside of the angle bracket so the rail is roughly centered over the 2x8. In the case of the 2x12s the first explanation should also work if I understand your question correctly.

The Iron Ridge software will give you the depth needed for the lags.

[SunEagle]

Isn't that the point of buidling codes ? Make-work for tradesmen and others ? You might be familiar with NEC 404.2(c) ? No, I'm being cynical. I think the main point of this hoop is the bldg inspectors covering their asses if the installation self-destructs.

Anyhow, I'm quite clear that you do not approve of using wood for the frame and that you think my PE's work is incomplete.

I have seen a lot of ground mounted systems that are built out of wood.

Since we have some pretty high wind loading here in Fl due to hurricanes I am sure a PE signed off on the drawings or the AHJ would not have approved the installation.

I was just surprised with the 6x6 since most installs I have seen use a 4x4 but they may have double the number of posts that you have used.

[RShackleford]

If so, what's the OP paying for ... or blood money akin to the price of admission to code compliance by jumping through some bureaucratically imposed hoop ?

Isn't that the point of buidling codes ? Make-work for tradesmen and others ? You might be familiar with NEC 404.2(c) ? No, I'm being cynical. I think the main point of this hoop is the bldg inspectors covering their asses if the installation self-destructs.

Anyhow, I'm quite clear that you do not approve of using wood for the frame and that you think my PE's work is incomplete.

[RShackleford]

The Iron Ridge design tool can tell you of the XR1000 rail can span that distance.

There's no question in my mind that it can. If I give their design tool a 4x4 array (landscape orientation, which is all they support) with the proper environmental conditions (120mph winds, class B exposure, 20psf snow), it works with only two cross pipes and a 7'6" spacing between them. My PE's drawing shows an 8'8-1/4" spacing, so I'd have to resolve that.

If the building authority resists a modification of that engineering drawing you could always add smaller profile Iron Ridge rails on to your engineered structure.

Good point. My purpose for using the IR rails is twofold: to mitigate the wood-warpage problem, and to make the panel mounting easy (with their UFO bolts). Certainly any grade of rails accomplishes the latter. I'd have to ponder how to attach the rails to the 2x8s so warpage of the wood doesn't bend the rails. And if I'm able to delete (all but two of) the 2x8s and use XR1000, I need to figure how to attach the XR1000s to the twin 2x12s.

[Ampster]

The Iron Ridge design tool can tell you of the XR1000 rail can span that distance. If the building authority resists a modification of that engineering drawing you could always add smaller profile Iron Ridge rails on to your engineered structure.

[J.P.M.]

It looks like there are diagonal braces in the design which may have given the engineer enough confidence that all he needed to account for was uplift and side loading. That is perhaps why he specified that particular model of post anchor. Simpson does make post anchor's that counteract bending forces better than the one spec'd in those drawings. Some embed in the concrete of the piers but may have required more concrete.

That may be, but I'd not make that call. However, if some engineer did do something so dismissive without checking that portion of the design, that's an example, IMO only, of perhaps unsafe or at least unprofessional and sloppy engineering.

If so, what's the OP paying for - a safe design, fit for purpose design or blood money akin to the price of admission to code compliance by jumping through some bureaucratically imposed hoop ?

Without the calcs, the site conditions and duty, and a bill of materials for the array, it's impossible for me to comment on the safety or suitability of what some engineer signed off on.

Not saying the design is unsafe or that it's not fit for purpose. Just that without more information I can't say so. And, if I can't, others with the similar necessary engineering expertise probably can't. Moving further down the food chain of engineering competence, my opinion is that there is a high probability you can't either.

The way I learned my engineering, the engineer does the design, or as is often done, the engineer checks the stresses developed by the required loading combinations for the site conditions and location for a design that was done by others. The engineer then modifies the design for safety, strength, code compliance or other reasons as the engineer deems necessary. That's usually more than a glance, especially for major structural components.

In doing so, all the loads and loading combinations deemed important by the engineer to the safety and structural integrity of the structure, as well as other considerations need to be checked and accounted for, and all the developed stresses and reactions compared to allowables.

Usually that means more than a cursory glance.

Besides, and to my limited experience, people who understand that codes and checking compliance to such codes is more than simply a reason to screw people out of money and put roadblocks to progress in their way usually expect more for their $$ than a casual lazy eyeball.