mounting panels to treated-wood frame

[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]

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.

[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.

[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.

[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]

Ironridge sells another system called FlashFoot2 which uses a lag bolt to hold a post to rafters instead of an L-foot. That lag is 5/16 x 4.75". If you use the same size bolt for the L-foot, it would seem that you will be as strong as a FlashFoot2, which seems to be adequate for virtually any system.

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.

[Ampster]

Ironridge sells another system called FlashFoot2 which uses a lag bolt to hold a post to rafters instead of an L-foot. That lag is 5/16 x 4.75". If you use the same size bolt for the L-foot, it would seem that you will be as strong as a FlashFoot2, which seems to be adequate for virtually any system.......

Keep in mind that the penetration of the lag on the FlashFoot is less than 4.75" because the FlashFoot has a raised bushing but even if it is a 1" bushing that is a 3.75" penetration which sounds pretty good to this non engineer.

[bob-n]

Ironridge sells another system called FlashFoot2 which uses a lag bolt to hold a post to rafters instead of an L-foot. That lag is 5/16 x 4.75". If you use the same size bolt for the L-foot, it would seem that you will be as strong as a FlashFoot2, which seems to be adequate for virtually any system.

Disclaimer: I am not a structural engineer. Please don't consider my word as an engineer signing off on the plan.

[RShackleford]

I used some cad plated lags initially on my patio cover and they rusted quickly presumably because of the interaction with the wood treating chemicals. I discovered this six months later when I was re-configuring my system so I replaced them with stainless steel which I believed has more tensile strengths. Galavanized could have been an option.

HDG (hot-dipped galvanized) should perform better. But this MCA-treated lumber is supposed to be gentler on fasteners: http://tarheelwoodtreating.com/produ...treatment.html ... citing that it's as good as CCA (the "old-fashioned" method, I believe) or un-treated, and they explicitly say aluminum contact is ok.

Stainless is not always stronger. From boltdepot-dot-com: "It is a common misconception that stainless steel is stronger than regular steel. In fact, due to their low carbon content, many stainless steel alloys cannot be hardened through heat treatment. Therefore, when compared to regular steel, the stainless alloys used in bolts are slightly stronger than an un-hardened (grade 2) steel but significantly weaker than hardened steel fasteners." However, somewhere else I read that HDG is always grade 2, so the SS would be slightly stronger.

With regard to your earlier comment about using two angle brackets on each beam, I think it may depend on on the angle that the IR intersects with your beams.

My elevation angle will be 25 degrees, so multiplying the 1.5" between the two 2x12 plies of my beam by the tangent of 25 degrees gives me a 0.7" height difference. I measure just under a 1" range of where the square-bolt can be in the slot on the L-foot (thanks to the nifty sample kit that IR sent me, two of them for some reason), so I'm probably ok. But staggering the 2x12s is a thought; might be a little weird where I cut out a 3" deep notch in the 6x6s to "let in" the beams (way stronger, and a neater look). The best plan might be to trim 3/4" off the edge of one of the 2x12s; pretty tricky to run a 20ft board thru a table saw though, maybe just do it with a circular saw with a rip fence.

[Ampster]

..............
As far as material, I think HDG or SS would be ok. Both are supposed to be fine with treated wood, esp. this MCA stuff I'm gonna use. SS with aluminum is bad medicine for galvanic corrosion, so maybe should use HDG; OTOH, IR seems fine with SS against their aluminum materials, I guess because it's anodized.

I used some cad plated lags initially on my patio cover and they rusted quickly presumably because of the interaction with the wood treating chemicals. I discovered this six months later when I was re-configuring my system so I replaced them with stainless steel which I believed has more tensile strengths. Galavanized could have been an option.

With regard to your earlier comment about using two angle brackets on each beam, I think it may depend on on the angle that the IR intersects with your beams. One leg of of the angle brackets does have a slot but I don't know if it is long enough to accommodate the distance to the rail from the beam on the side opposite the apex of the beam and rail. If you felt you needed two bolts you could stagger the two pieces of your laminated beam in stair step fashion so the bottom of the rail intersects with the tops of both parts of the laminated beam. Another option would be longer bolts and a spacer to elevate the angle bracket to accomodate the higher part of the rail. You have a lot of options to add extra strength beyond the minimum required without adding much cost or effort.

[RShackleford]

And you probably won't.

Yeah, I realize I'm off the reservation. OTOH, using the L-feet in a pitched-roof scenario is totally supported by IronRidge, so I'm surprised they don't say something. If those figures existed, I realize they wouldn't quite work for me, since ground-mount will have higher wind loading. But at least they'd be a starting point.

The lag dia. and embedment length are mostly, but not entirely f(pullout load) which varies with location and application and also depends on the type of structure and the wood it's made of as well as the rails and racking.

Everything from the square bolts (which connect the rails to the L-feet) on up is good, since those same bolts are apparently used for the "bonded rail connectors" which connects rails to locally-sourced steel pipe in the supported ground-mount application (https://www.renvu.com/Solar/IronRidg...nch-GM-BRC-002).

As far as the lag bolts, with the proper loads, I could go to the Timber Construction Manual, which specs withdrawal loads for various diameters, embedment depths, and wood species.

What would be great would be a heavier duty version of https://www.manasquanfasteners.com/p...xoCgAsQAvD_BwE , so that it could be thru-bolted to my two-ply 2x12s.

[J.P.M.]

Hi @Ampster I have looked and looked and cannot find any guidance on what size lag bolts IronRidge wants you to use for attaching the L-foot to the wood. I even ran through a trial design for pitched roof (where the L-feet are lagged to the rafters) but still can't find anything. Can you give me a pointer or hint ? Thanks.

And you probably won't. The lag dia. and embedment length are mostly, but not entirely f(pullout load) which varies with location and application and also depends on the type of structure and the wood it's made of as well as the rails and racking.

See for example, National Design Specification for Wood Construction, ANSI/AF&PA NDS 2018, "National Design Standard for Wood Construction" . Para. #'s 12.1.4, p.74 and 12.2.1, p..76 for a start on calcing allowable design strength withdrawl capacity. There may be a newer version, but that's the last version I used.

You'll need all the imposed external loads and loading combinations before you start.

[RShackleford]

I did not find that on the Iron Ridge diagrams but I found two different permits over the years from the same city. One permit used 3/16 x3 1/2" lags and another used 3/8 x 3".lags. The critical load is uplift. FWIW the spacing of the lags was 4 feet.

The hole can take 5/16", maybe 3/8" really tight (the hole diameter is inexplicably absent from the cut sheet from IR). .

I totally agree it's all about uplift and I do worry a little that my spacing is close to 8ft (between L-feet on a 13ft rail). We know the rail can span that (per IR's ground-mount design tool), but that's clamped to pieces of steel pipe. However the roof-mount tool allows 96" joist spacing too, but wind-loading is obviously less since it's just above the roof. So I really want belt&suspenders on my attachments. It looks like the "bonded rail connector" (for attaching XR1000 to horizontal steel pipe in ground-mount) has two of the bolts that connect to the rail. So maybe I oughta use two L-feet at each end.

As far as material, I think HDG or SS would be ok. Both are supposed to be fine with treated wood, esp. this MCA stuff I'm gonna use. SS with aluminum is bad medicine for galvanic corrosion, so maybe should use HDG; OTOH, IR seems fine with SS against their aluminum materials, I guess because it's anodized.

[Ampster]

Hi @Ampster I have looked and looked and cannot find any guidance on what size lag bolts IronRidge wants you to use for attaching the L-foot to the wood. I even ran through a trial design for pitched roof (where the L-feet are lagged to the rafters) but still can't find anything. Can you give me a pointer or hint ? Thanks.

I did not find that on the Iron Ridge diagrams but I found two different permits over the years from the same city. One permit used 3/16 x3 1/2" lags and another used 3/8 x 3".lags. The critical load is uplift. FWIW the spacing of the lags was 4 feet.

[RShackleford]

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.

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

Hi @Ampster I have looked and looked and cannot find any guidance on what size lag bolts IronRidge wants you to use for attaching the L-foot to the wood. I even ran through a trial design for pitched roof (where the L-feet are lagged to the rafters) but still can't find anything. Can you give me a pointer or hint ? Thanks.