mounting panels to treated-wood frame

[littleharbor]

Probably decreased uplift on the array a fair amount but I suspect the addition didn't eliminate as much of the uplift as you might think.

For starters, most winds probably aren't normal to the rear of the array. Those from a non oblique angle, but still from behind the array, will result in some uplift. Then, there's the venturi effect "sucking" at the front of the array. Not all uplift is from wind force "pushing" against the back of the array. Depending on wind direction, you will also see some compressive loading in the array supports that are parallel to (in the plane of) the panels, increased compressive loading and shear at the array anchorages at the front and some uplift where the fence attaches to the roof. Just sayin'. Did you run any calcs ?

I wouldn't know how to run calcs. Besides some wind protection I put up this fencing for aesthetic reasons.

[RShackleford]

We have lots of winds here in Baja and even Hurricane Rosa passed right over us last year. I was concerned with the wind getting under my array and built this dog eared cedar "wind break" to decrease the uplift on my array. 4 years have passed without any perceivable problems.

How are your panels mounted ? Turnkey metal racking system, or something more adhoc like I'm doing ?

[J.P.M.]

Not sure if this will be helpful or just throwing a wrench into the works. After 6 pages of comments I figured, why not?

We have lots of winds here in Baja and even Hurricane Rosa passed right over us last year. I was concerned with the wind getting under my array and built this dog eared cedar "wind break" to decrease the uplift on my array. 4 years have passed without any perceivable problems.
DSCN4732.JPG

Probably decreased uplift on the array a fair amount but I suspect the addition didn't eliminate as much of the uplift as you might think.

For starters, most winds probably aren't normal to the rear of the array. Those from a non oblique angle, but still from behind the array, will result in some uplift. Then, there's the venturi effect "sucking" at the front of the array. Not all uplift is from wind force "pushing" against the back of the array. Depending on wind direction, you will also see some compressive loading in the array supports that are parallel to (in the plane of) the panels, increased compressive loading and shear at the array anchorages at the front and some uplift where the fence attaches to the roof. Just sayin'. Did you run any calcs ?

[littleharbor]

Not sure if this will be helpful or just throwing a wrench into the works. After 6 pages of comments I figured, why not?

We have lots of winds here in Baja and even Hurricane Rosa passed right over us last year. I was concerned with the wind getting under my array and built this dog eared cedar "wind break" to decrease the uplift on my array. 4 years have passed without any perceivable problems.
DSCN4732.JPG

[bob-n]

RShackleford,

You clearly know construction and will have no trouble doing it. This tip will be unnecessary, but I'll share it anyway. Please don't take offense.

For those long lag bolts, an impact driver will come in very handy, even for pre-drilled holes. I tried a conventional, decent-quality Ridgid driver and it couldn't put the bolts all the way in. A friend loaned me his Milwaulkee impact driver and it installed the bolts effortlessly.

[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.

[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]

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.

[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]

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).

[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]

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.

[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]

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]

......... 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.