mounting panels to treated-wood frame

[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.

[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.

[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.

[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.

[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.

[Ampster]

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.

Are you suggesting the OP should walk away from his design and the cost of engineering and go to an entirely metal structure? Or are you just saying he should use metal racking on his wood structure.

[RShackleford]

AHJ is fine replacing the 2x8s with rails, if I can document the rails' ability to span the dual-2x12 beams. I can do that simply by showing a design created by IronRidge's design tool, for a similar 4x4 array. It comes up with eight 14ft XR1000 rails supported by two pipes separated by 7'6". And outlined how I would address the diagonal bracing (in the absence the 2x8s) and it seemed like he could be satisfied without too much trouble.

There's a local supplier who will sell me the XR1000s and the 40 UFO's for about $680. No delivery fee, if delivery is at his convenience (has already has a truck in the area), which is great. It's still a lot of cost to add to this design I'm trying to do on the cheap. All I save is the 8 2x8s, the 16 connectors to attach them to the beams, the clamps and lag bolts, and the ground clips - I'm thinking about $300-400. And I still need some hardware to attach the XR1000s to the beams (I guess that's only about $50 for16 L-foots and 16 rail-connector bolts). Of course, I also get some ease of construction (e.g. don't have to precisely locate the positions of the clamp/lagbolts, or ground each panel), and, the main reason I'm considering this: less concern with wood warpage (I suppose the dual-2x12 beams could warp a little, but that's just slippage at the ends of the XR1000s.

An intermediate plan would be to keep the frame with 2x8s as designed, but add rails, but that needn't be beefy enough to span the beams. Rails must be IronRidge or QuickMount brand, because that's all this no-delivery-fee outfit carries.

[Ampster]

...... (I suppose the dual-2x12 beams could warp a little, but that's just slippage at the ends of the XR1000s.

Glue and screw the 2x12s together and they should stay stable.

[J.P.M.]

Are you suggesting the OP should walk away from his design and the cost of engineering and go to an entirely metal structure? Or are you just saying he should use metal racking on his wood structure.

No. You smokin' something ? Or just trying to give me some B.S. ?

If you infer something like that into what I write, you're seeing more than is there.
Read what I wrote in the context of the post I was responding to and don't read things into my post that are not there.
If you examine my posts to this thread, or any other post I've ever written for that matter, nowhere will you find where I suggested walking away from a design based on materials alone.
I just think that, based on what I think I might know from experience, training and education, that for the safest, most fit for purpose and when all factors are considered, there are better materials for the structural support of PV arrays than wood.

In the post I responded to above, the OP stated he was trying to minimize costs. Looks to me that he is considering only first costs. If so, and keeping in my mind that others may be reading all this stuff, what I am suggesting, for others' benefit more than the OP's, is that there may be other things to consider in costing a project besides initial or first costs - things like maintenance (painting/treating/replacing the wood comes to mind) and wear/tear, not to mention what are, IMO only anyway, the more likely negative effects an aged wood structure may have on perceived resale values. As stated previously in the same post I was responding to, NOMB what RShackleford does. If so, why would you think I would be contradicting "NOMB" by suggesting he walk away ?

I believe we (he and I) understand that we see the value of wood as a construction material differently. I believe you need to bone up on reading comprehension skills.

[RShackleford]

... there are better materials for the structural support of PV arrays than wood.

I believe you need to bone up on reading comprehension skills.

I believe you need to bone up on your memory skills, because you've said this SAME thing over and over again in this thread. I get the point. Please stop it, if you have nothing new to add.

[RShackleford]

Glue and screw the 2x12s together and they should stay stable.

Yeah, especially if I were clever enough to arrange the grains on the two boards so any warpage cancelled out.

But my point was, if I use the IronRidge rails (and delete the 2x8 purlins), and attach the ends of the rails with the "L-foot" and "rail connector bolt", that bolt could be a little loose (how to calibrate that ?) so that as the 2x12s bend (warp), there's a little free play as the rail-connector bolt slides in the rail groove.

I think I've sold myself on this plan to replace the 2x8s with XR1000s. Gonna add a few hundred dollars to the overall cost (out of about $7000, before federal credit), but will make it easier to install (imprecisions in the carpentry can readily be cancelled out with rail mounting, and no panel-mounting holes to drill), should address some of JPM's concerns with wood (the warpage issue, if not the issue of deterioration of the wood), and should make it look better (more of a "floaty" effect).

[J.P.M.]

I believe you need to bone up on your memory skills, because you've said this SAME damn thing over and over again in this thread. I get the point. Please stop it, if you have nothing new to add.

My memory is fine (I think). I'm fully aware of what I write. In this case, I was responding to Amster's post and what I see as more of his argumentative B.S.

As for you: Apparently, you missed my thrice made statement about what you do being none of my business. You can make array supports out of tree branches for all I care.

Just don't tell me what to write.

You don't like what I write, stop reading it.

Ever stop to think that others besides you may get some use of it ?

This forum is more than just about you, me or any single person. I try to keep that in mind.

[RShackleford]

Ever stop to think that others besides you may get some use of it ?

So which time that you said wood isn't your favorite construction material will be the time that others get some use out of it ?

[Mike90250]

Gentlemen, cool your engines. It's been said several times (all of it) by several parties.

[Ampster]

Yeah, especially if I were clever enough to arrange the grains on the two boards so any warpage cancelled out.

But my point was, if I use the IronRidge rails (and delete the 2x8 purlins), and attach the ends of the rails with the "L-foot" and "rail connector bolt", that bolt could be a little loose (how to calibrate that ?) so that as the 2x12s bend (warp), there's a little free play as the rail-connector bolt slides in the rail groove.
.......

Warpage in wood has been overblown in this thread. Just randomly gluing them together will produce a beam much stronger than an equivalent beam that is not laminated. I toured a laminated beam mill once and they just took the boards as they arrived at the assembly point. A tube of construction adhesive per beam should suffice. Screwing the beams together should provide sufficient clamping force to maximize the surface area of the glue and wood.

Also, I would tighten the connector bolts between the aluminum rails and beams. Those rails are strong enough in compression and tension to take any loading that slight warpage could put on them. That way the 8 rails and laminated 2x12s work as a system that will be much stronger than one with loose connections. You can test that by trying to shake the structure before and after tightening the bolts. In addition once the panels are clamped to the rails you will get a diaphragm effect that will further contribute to its stiffness. I am not an engineer but I have been working around wood frame construction most of my life and discussed similar issues with engineers and architects numerous times.

As far as documenting the SR rails ability to span the distance, the Iron Ridge site should help. If you haven't dug the holes and poured the concrete yet, you might be able to move them closer to cantilever the rails a little more. That will allow you to shorten the span. The Iron Ridge site can give you some guidance with that.

Hopefully this simple and practical advice will help other readers. If this were a bridge or a multistory apartment building I would not be offering these opinions.