mounting panels to treated-wood frame

[Ampster]

Thanks. Yeah, that's a good data point. However, I imagine ground-mount is subject to much higher wind uplift loads than roof-mount. So I think I need to be looking at IR's products for ground-mount. In particular, that "bonded rail connector" that connects an XR1000 rail to locally-sourced 2" or 3" steel pipe, looks like it uses TWO bolts to attach the rail to the piece of angle; so I'm kinda thinking I need that, regardless of how securely the L-feet are lagged to the 2x12s.

I think it depends on what is upwind of the prevailing winds. I installed a system on a 3rd story roof at the peak of a small hill and if I remember the calcs there may have been a venturi effect.on that installation. You will always be safe by assuming the worst cast.

[RShackleford]

I think it depends on what is upwind of the prevailing winds. I installed a system on a 3rd story roof at the peak of a small hill and if I remember the calcs there may have been a venturi effect.on that installation. You will always be safe by assuming the worst cast.

Well that's a point. Even though I'm exposed to more wind by virtue of being ground-mount, I'll be much closer to the ground than any roof (about 8ft at the high end). Also, the max design wind here is 115mph, whereas the XR1000 rail is allowed to span 8ft even with 160mph winds (see attached). I'll run their design tool with 160mph and see what it wants for rail attachments.

[J.P.M.]

If you two want to do this in a professional manner and get serious rather than all the blather and hearsay, consult ASCE 7- 05, ASCE 7-10, et seq. Neither of you has a clue what's required.

[Ampster]

If you two want to do this in a professional manner and get serious rather than all the blather and hearsay, consult ASCE 7- 05, ASCE 7-10, et seq. Neither of you has a clue what's required.

Does it matter if he exceeds what is required? His goal is to get a permit.

[RShackleford]

Does it matter if he exceeds what is required? His goal is to get a permit.

Oh, I've got my permit. But my goal is to make a good structure. However ...

Neither of you has a clue what's required.

I kinda do. Because I paid a licensed professional engineer to draw up the plans I used to get the permit, an he did do those calculations. I'm diverging from them a bit, with the inspector's blessing. But the necessary fastener strength he computed for the original 2x8 purlins also works for the XR1000 rails (same number, of same length, in same configuration); and for those, he spec'd Simpson H1 (good for 480lb uplift).

[Ampster]

......... and for those, he spec'd Simpson H1 (good for 480lb uplift).

It is not too difficult to get several opinions about the pullout strength of a lag bolt in various species of lumber. Exceeding those most likely will pass inspection. Throughout this dialogue the OP has demonstrated enough common sense that I am sure he will have a safe project. I am not an engineer but I have spent over 60 years in various aspects of construction with success dealing with inspectors. engineers, and architects in the field.

[RShackleford]

It is not too difficult to get several opinions about the pullout strength of a lag bolt in various species of lumber.

Yes, in fact, there's a tome called the Timber Construction Manual that has extensive tables.

[Ampster]

Yes, in fact, there's a tome called the Timber Construction Manual that has extensive tables.

I have supervised the construction of some large steel buildings and the engineering is complex compared to a patio cover. It is not hard to get 500 lbs of pullout strength in wood by simply using a longer lag.

[RShackleford]

Well that's a point. Even though I'm exposed to more wind by virtue of being ground-mount, I'll be much closer to the ground than any roof (about 8ft at the high end). Also, the max design wind here is 115mph, whereas the XR1000 rail is allowed to span 8ft even with 160mph winds (see attached). I'll run their design tool with 160mph and see what it wants for rail attachments.

Ran IR's ground-mount tool with 180 mph winds and it was still happy with XR1000 spanning 8ft and with one "bonded rail connector" at each end. Each bonded rail connector connects to the rail with two bolts. Given my 115mph design wind speed, I'm thinking one is enough. Be good to get a spec from IR on that bolt (connection to XR1000) though.

[bob-n]

I once phoned Ironridge and their engineer was happy to talk to me. It couldn't hurt to give it a try.

[RShackleford]

I once phoned Ironridge and their engineer was happy to talk to me. It couldn't hurt to give it a try.

I did, and they suggested using the "pitched roof" tool, since that uses the L-foot attachment. Yes, wind uplift is gonna be higher on ground-mount than an equivalent roof-mount. However, the pitched-roof tool tells you what the uplift force is at each point of attachment.

With ASCE 7-10, 120mph wind (exposure B), 20psf snow, 25-degree roof slope, a 4x4 array (of 60 cell panels), and XR1000 rails w/ attachments about 8ft apart, it computes 733 lb of uplift at the "zone 3" points of attachment - yet it specs a single L-foot (for each point of attachment).

[J.P.M.]

I did, and they suggested using the "pitched roof" tool, since that uses the L-foot attachment. Yes, wind uplift is gonna be higher on ground-mount than an equivalent roof-mount. However, the pitched-roof tool tells you what the uplift force is at each point of attachment.

With ASCE 7-10, 120mph wind (exposure B), 20psf snow, 25-degree roof slope, a 4x4 array (of 60 cell panels), and XR1000 rails w/ attachments about 8ft apart, it computes 733 lb of uplift at the "zone 3" points of attachment - yet it specs a single L-foot (for each point of attachment).

How did you come the conclusion that the uplift on a ground mounted array will be greater than an equivalent roof mount ? Maybe it will be, maybe not.

Another question: What is the pullout strength at the point of attachment between the fasteners you're using and what they're attached to, and how are you calcing that number ?

Hopefully, the pullout strength of such connections will be > the pullout load.

[RShackleford]

How did you come the conclusion that the uplift on a ground mounted array will be greater than an equivalent roof mount ?

I said that as an aside. But how could it not be ? It's fully-exposed to any wind, whereas roof-mount is just a few inches above your roof. The only other issue is that ground-mount is typically much lower than any roof; mine is going to be about 3-9ft above grade.

Another question: What is the pullout strength at the point of attachment between the fasteners you're using and what they're attached to, and how are you calcing that number ?

IR's pitched-roof calculator (with the inputs I quoted above) told me that the attachments, which are L-feet lagged into rafters, will see up to 733lb of uplift. So they're saying the L-foot and its attachment to an XR1000 can handle at least that much. They don't seem to spec the lag attachment to the rafters, saying it should be stainless of 5/16" diameter but not spec'ing the embedment depth as best I can tell; however, this calculator: https://www.awc.org/codes-standards/...connectioncalc tells me that 4" embedment will give me 700 lb (see attached screenshot).

Hopefully, the pullout strength of such connections will be > the pullout load.

As I said before, my engineer's sealed drawing specs Simpson H1 connectors, which is spec'd for 480lb uplift. The L-foot connection will exceed that by a large margin.

I'm a little bemused that IronRidge is happily concatenating aluminum with stainless steel (the UFO connectors as well as the bolts which join the L-foot to the rails), which is a bad match for galvanic corrosion. I guess the answer is that the aluminum is anodized.

[Ampster]

.......
With ASCE 7-10, 120mph wind (exposure B), 20psf snow, 25-degree roof slope, a 4x4 array (of 60 cell panels), and XR1000 rails w/ attachments about 8ft apart, it computes 733 lb of uplift at the "zone 3" points of attachment - yet it specs a single L-foot (for each point of attachment).

That would be a long lag bolt. I presume that if you use two L feet at each end you could figure. 375lb of uplift?
To be clear, I am not an expert, but common sense can provide some insight to test assumptions.

[RShackleford]

That would be a long lag bolt. I presume that if you use two L feet at each end you could figure. 375lb of uplift?

I am now seeing no need to use two L-feet at each end. As I said in post #73, the 4" lag bolt gives me 700+ lb. That doesn't seem excessively difficult to install.

I could always fabricate my own extra brackets from hanger strap, wrap it over the top of the rails (there'll be no UFOs near the 2x12s) and nail it into the side of the 2x12. Kinda kludgy.

The worst wind weather event to ever strike my area (Hurricane Hazel, 60+ years ago, since records kept) sported 75mph sustained winds and 90mph gusts. My installation will never see winds anything like that, due to surrounding trees; and if winds that heavy ever do hit the area, it will be demolished by falling trees well before there's a risk of it suffering wind damage.