Panels as Sheathing?

[Kornbread]

It’s the acidic action of the treatment agents that is the major problem with pressure treated wood, not the copper.

CCA plywood in aluminum boats, for example, never caused short-term issues, nor did it create failures of fasteners with high rise building balconies or the semi truck aluminum trailers that delivered from the plants to the yards of retailers and distributors.

Aluminum and stainless DOES make for bad juju, but for whatever reason it seems to go years without issue in boats, especially when painted. I don’t know why because on paper: it shouldn’t.

I should have included the link in the quote concerning cca/ca and copper being the culprit as I do not know if this is the reason, or the sole reason for the increased reactivity vs older treated lumber. A quick search says " ... chemicals used to treat this wood were revised in 2003 to remove some of the potentially harmful elements in the treatment. The change in chemical formulations increased the corrosivity of the wood when in contact with metal parts. The two most popular chemicals for wood pressure treatment are alkaline copper quaternary (ACQ) and copper azole (CA), which are both active corrosion materials. ... " American Galvinizers Association I do use special fasteners when building decks with treated lumber.

Thinking out loud ...
I have only used marine grade plywood in boats. The main difference between marine grade and 'reg' grade is in the glue. AFAIK, it is not treated, although, if using treated wood, it would stand to reason that a nonporous painted surface between the differing materials, might, mitigate a reaction. Curious, do you know which wood treatment method was used in the applications you mention?

... and with a bit more research, it appears not all treated lumber is cca/ca and may actually be aluminum friendly.

Back to the OP and mounting panel sheathing directly to what is basically a pole barn. The OP may be able to source the aluminum friendly lumber, or possibly a simple barrier of paint between the panel's frame and lumber might suffice. It would be interesting to know the long term outcome.

 

[Kornbread]

This thread is very interesting as I do plane on a shop building. In my case, panels would not be ideal for the main roof, but a 'lean-to' to shelter the cars, tractor, boat, etc., would be a most excellent idea.

 

[12VoltInstalls]

The main difference between marine grade and 'reg' grade is in the glue. AFAIK, it is not treated,

No.

ACX is indicative of exterior glue in the laminations with the X. Marine plywood = same glue.

The main difference between marine and ACX fir plywood is that the marine plywood laminations contain no voids, and surface ‘footballs’ are not allowed due to the fact that marine plywood cannot have stress risers where it could fail as it is molded or formed to the continuously varying shape of a boat hull.

Marine plywood is for boat hulls.

 

[eXodus]

Aluminum and stainless DOES make for bad juju,

Stainless and aluminum are actually almost polar opposites on the galvanic chart my friend.

neither aluminum nor stainless are used pure in modern products. Usually they are alloys mixed with something else.

That's why in practical applications it is very common to have stainless steel fasteners in Aluminum. Usually those bolts and nuts are a special kind of stainless which is more compatible with the aluminum used in solar applications. BUT! there are usually not bolts threaded directly into Alu

You got a stainless nut and bolt clamping an aluminum member.

 

[Short_Shot]

neither aluminum nor stainless are used pure in modern products. Usually they are alloys mixed with something else.

That's why in practical applications it is very common to have stainless steel fasteners in Aluminum. Usually those bolts and nuts are a special kind of stainless which is more compatible with the aluminum used in solar applications. BUT! there are usually not bolts threaded directly into Alu

You got a stainless nut and bolt clamping an aluminum member.

Well that's not really true. The chart clearly shows alloys of both and where they typically lie. There's no such thing as "pure stainless steel" either. All SS is an alloy, and the pointed out spot on the chart IS "aluminum alloys". Facts is facts.

HOW its fastened plays a part in reducing it, but it doesn't change the matter. The reason most people get away with it is that the aluminum oxide has a different value from the aluminum itself... which gets to your point about threading vs nuts/bolts. You are right that threading right into the aluminum is worse though for sure. That's where most of the corrosion I find at work starts, until the whole aluminum part is rotted away.

I still use stainless and aluminum myself, but only when its not going to be exposed to saltwater from roads and such. I have had many examples of aluminum stuff and stainless fasteners rotting out at work where we use bromine salt at a really low dilution rate (much lower than rain/road salt) after only a few years of use.

 

[eXodus]

but only when its not going to be exposed to saltwater from roads and such.

which should be the case for the majority of roof mount solar systems on homes, RV, sheds etc.

Excluding Marine environments.

threading vs nuts/bolts

some of the higher end stainless bolts have some sort of finish on them.

aluminum oxide

maybe that's why it's working - the stainless is coated and the oxide is not reactive to whatever it was coated in?

 

[Short_Shot]

RVs are definitely exposed. My entire truck and trailer gets covered top to bottom during winter travel in a *thick* layer of salt

 

[Short_Shot]

which should be the case for the majority of roof mount solar systems on homes, RV, sheds etc.

Excluding Marine environments.


some of the higher end stainless bolts have some sort of finish on them.

maybe that's why it's working - the stainless is coated and the oxide is not reactive to whatever it was coated in?

The stainless wouldn't be. The aluminum is.

Stainless by definition doesn't form much/any oxide layer because that would just be rust.

 

[WYtreasure]

Sounds like a great idea.
I don't think anyone has addressed the reason "sheathing" is used when building a 2x4 structure. Here's one definition of sheathing: A layer of boards or of other wood or fiber materials applied to the outer studs, joists, and rafters of a building to strengthen the structure and serve as a base for an exterior weatherproof cladding.

Find some way to strengthen the structure as sheathing would do and go for it.

 

[Kornbread]

Yes, wafer board, plywood, whatever sheet goods is used, adds considerable structural integrity. I had to add sheathing to all four coroners of the lower level of our house before starting work on the upper floor. Huge improvement in stability. The OP wants to use this on a 'small' barn. No idea how small, but around here, most barns, large barns, have a tin roof. No sheathing. I'd have to wonder if PV panels might add similar strength to the building as a tin roof.

 

[WYtreasure]

Yes, wafer board, plywood, whatever sheet goods is used, adds considerable structural integrity. I had to add sheathing to all four coroners of the lower level of our house before starting work on the upper floor. Huge improvement in stability. The OP wants to use this on a 'small' barn. No idea how small, but around here, most barns, large barns, have a tin roof. No sheathing. I'd have to wonder if PV panels might add similar strength to the building as a tin roof.

I think the shed is fairly small, OP mentioned 12' wide.

The tin itself is a sort of sheathing, not like plywood but many times it is sufficient. My concern is the relatively small size of a solar panel vs a sheet of plywood or tin.

I've seen cables used for stability on some large tin roofed barns.
Cables may be an adequate stabilizer for the OP.

 

[Kornbread]

I think the shed is fairly small, OP mentioned 12' wide.

The tin itself is a sort of sheathing, not like plywood but many times it is sufficient. My concern is the relatively small size of a solar panel vs a sheet of plywood or tin.

I've seen cables used for stability on some large tin roofed barns.
Cables may be an adequate stabilizer for the OP.

... or maybe some 2x4 screwed in a diagonal across the wall/roof?

 

[eXodus]

I think the shed is fairly small, OP mentioned 12' wide.

The tin itself is a sort of sheathing, not like plywood but many times it is sufficient. My concern is the relatively small size of a solar panel vs a sheet of plywood or tin.

I've seen cables used for stability on some large tin roofed barns.
Cables may be an adequate stabilizer for the OP.

My 40 ft x 32 barn is made out of 6x6 posts. The roof trusses are 2x6 and the rafters are 2x4.

Just tin roofing on it. 5v Crimp.

It has zero sheeting and survived a cat 3 hurricane at least twice here in Florida, since I bought the the place. No idea how long the structure is already here.

I guess most of the strength of the building comes from the 6x6 poles which are 2- 3ft in the ground ever 8ft spaced.

I would absolutely sheet this building with the new 40x80inch 400-500w panels. These panels are sturdy as heck. Would add way more regidity to the barn the the tin roofing.

Probably would have to upgrade the trusses and rafters for the higher weight. But when it's a pole barn I don't see a issue

 

[12VoltInstalls]

tin itself is a sort of sheathing, not like plywood but many times it is sufficient

... or maybe some 2x4 screwed in a diagonal across the wall/roof?

For a 12’ building probably not a big deal but even with metal roof diagonal bracing is a necessity. Never mind uplift for stormy weather or tornadoes nearby!
Depending on the solar panels for torsional support seems like a very misguided idea.

 

[eXodus]

For a 12’ building probably not a big deal but even with metal roof diagonal bracing is a necessity. Never mind uplift for stormy weather or tornadoes nearby!
Depending on the solar panels for torsional support seems like a very misguided idea.

12ft is really not that big.

But a few corner cross braces do not hurt and with 2X4 cost next to nothing.

For sheeting with solar I would definitely use more then the usual 4 screws per panel. Maybe use a 20inch on center truss system to get 4 trusses underneath each panel. Would provide 8 mounting points per panel.

 

[CamoGreg]

Electricians I work with use noalox (available at home depot) to coat anything mounting to unistrut as a deterrent to galvanic corrosion.

 

[WYtreasure]

Electricians I work with use noalox (available at home depot) to coat anything mounting to unistrut as a deterrent to galvanic corrosion.

Welcome to the show CamoGreg,

Yep, noalox can save the day.

Wonder when the OP will be returning. Sounds like we've got some good ideas/info on the table.

 

[SignatureSolarJames]

Guys, the aluminum of a panel frame is anodized, the corrosion rate is beyond the panel life in my research

 

[Short_Shot]

Guys, the aluminum of a panel frame is anodized, the corrosion rate is beyond the panel life in my research

Research as in laboratory testing or reading on Google?

Because I've got an entire chiller system full of aluminum, stainless steel, and brass, and if we slack on corrosion inhibitors the aluminum is the first thing to go. Anodized or not doesn't matter.

Granted, outdoors you're simply subject to rain periodically so the rate at which it occurs will be much much slower than in a system constantly exposed to water, but that's basically just how accelerated testing works.

It may very well outlast the panel, but if you're in a rainy area or near the salty ocean it may not.

 

[Checkthisout]

Use the panels like rainscreen. Bolt them to each other with vycor (the decking joist protector sized roll would be perfect) between the panels to act as gasket/cushion.