Correction - Truth about Aluminum Framing [part 2]

[@PatrickRemington]

Would it not be simpler to just add a thicker insulation layer between the aluminum tube and the exterior panel? that way the aluminum won't see such a temperature difference.

[@cachecamper]

@PatrickRemington not simpler, but yes it would help with the condensation point. What I'd did not do a good job with in that video was sharing that we are not trying to stop moisture. We're channeling it somewhere. We want it to be on the inside of the tube. The moisture that is going to get in from the exterior, needs to be able to go straight into a tube rather than the insulation. So the sheeting is as close to the studs as possible. But you are correct, the insulation on the outside would significantly help reduce the thermal transfer on the studs but it is only solving one issue. Not the others.

[@surfingcuriositywaves4046]

One mechanism by which moisture moves is known as 'vapor drive', and it is a bit complex. Vapor holds moisture suspended in the gaseous state until the vapor gets to the 'dew point temperature', at which time the moisture condenses into water. This usually happens when the temperature condition causes condensation at the boundary layer of the cold surface as that cold surface cools the vapor boundary layer. Think of a glass of iced tea in the humid summer. After the moisture drops out of the boundary layer onto the cold surface, the moisture just beyond the boundary layer moves into that boundary layer and 'replenishes' the boundary layer moisture that just condensed. In this way, even when the air movement is very slow or none, the vapor drive moves that moisture to condense on cold surfaces. The goal of vapor retarders is to slow down that vapor transmission. Closed cell foam, if sealed at the edges properly, can be a very effective vapor retarder. However, as taught to me by Joe Lstiburek, the founder of Building Science Corp., we rarely build a perfectly sealed assembly, so we should provide for what to do with moisture when (not if) that moisture finds its way into an assembly. So vapor retarders slow down vapor transmission, but don't completely stop the transmission because we sometimes need to give the unwelcome water an easy path out by weepholes and semi-permeable vapor retarders. This is why we build houses in the north with walls that allow the wall assembly to 'dry to the inside'. It is quite complicated, but if you find some videos by Joe Lstiburek (yes that is spelled correctly) you will gain a better understanding of 'vapor drive'. One interesting thing to note is that there is a temperature gradient within the wall materials, (think of many layers at different temps). One of those temps can be at the dew point temp, at which place the moisture will condense on any nearby surface, which can even be on fiberglass fibers at the dewpoint temp in a wall assembly. A really well insulated stainless mug (holding iced tea from Alabama) won't have the condensation on the outside because the steel outside is a vapor barrier that doesn't let the vapor into the air or foam that is inside the mug's two stainless walls. That well insulated mug just doesn't let the vapor near the place inside its walls where the dewpoint temp layer exists. A poorly insulated mug is cold to touch on the outside surface, so it can be at the dewpoint temp and have condensation. BTW, the term 'sweat' does not accurately describe condensation, because sweat comes from inside us (glands produce it) and serves a cooling function. Condensation forms from vapor, a completely different process.

[@setheroth28092]

Interior screws penetrating the aluminum frame, combined with humans exhaling humidity in the camper - seems like it could provide all the moist air needed to get condensation in the frame. I wonder if expanding foam in the frame would prevent air intrusion in the first place.

[@cachecamper]

Very well delivered. Thank you! I actually had the temperature difference of each of those materials detailed out and decided not to add it to the video. The inside of each of those tubes is left clear and intended as a sort of channel for the moisture to escape and drain out to the exterior. Each of those fasteners ices up significantly in the brutal cold and those penetrate the studs. This in itself puts moisture in the wall. That is okay as long as there is a place for that moisture to go. You are so correct. The moisture WILL eventually compromise some area of the build. Can the build absorb that failure and maintain structural integrity and follow through with its mission over the life of the unit regardless. That is the question, as an applications designer and manufacturer, that must be answered with a yes. It may not be on paper the perfect setup to solve each categorys' issue, but how does it respond across the entire analysis. That is why we have done this particular type of build in this way. Thank you for putting that explanation together.

[@kenstaal1839]

@@cachecamper Thank you So much for the video, @surfingcuriositywaves4046 is absolutely right and i looks like you've addressed how to deal with the present moisture, thermal bridging is the main problem i am also trying to solve on a camper i am planning to build you videos are extremely helpful. one thing i will add to this conversation is that it is possible to prevent moisture in the tube, its just expensive you can purge the tube of air, and fill it with an inert gas. obviously this method does make sense in a camper application, but i wonder if you could fill each aluminum section with expanding foam, would it help with thermal bridging would it help prevent the fasteners freezing on the interior? food for thought.

[@cachecamper]

@kenstaal1839 you're welcome. I'm glad you're finding them helpful! That's awesome. It's all about the goal. I'm going to do a video on our mindset with insulation. If insulation was our only goal, we would do a composite SIP panel. But the other factors take place of insulation. But yes, in theory, that works. But moisture needs a place to go when, not if, it is generated.

[@Superthermal]

Structured argument: Your doing a great job. Structured reply: Thanks! Love the builds. Look awesome.

[@cachecamper]

@@Superthermal 😅 love it

[@djRockalot]

So do you add drain/weep holes to your studs?

[@cachecamper]

@djRockalot yes, at every joint. Then to the exterior when all rail is installed.

[@gi7892]

I agree that there isnt a lot of good videos on this. Thank you for your effort. I am more than willing to put up with some minor mistakes because i always read the comments and the discussion is almost always valuable. Thank You!

[@TABLESAWTIM]

After making several campers and trailers, from the beginning I'd drill ¼" hole's in the aluminum linear runs, where the opposing sections are to be welded, be it vertically or horizontally. Each ring run (bottom plate) had one common opening the width of the rectangle tubing, 3½" long with a slidable/adjustable valve vented to the outside air, also with a round pipe protruding through the top as a convection stack to the outside where all tube airspace columnate. These can be adjusted for optimal convection from the internal heat trying to escape and aids in cooling in the Summer. Four upper adjustable valve stacks one per side, with four lower per side would deliver far better results. No one else that I found, has done this, other than me. When in motion the stack/s as a venturil effect. Enjoy

[@TribalGlobe]

Better video. I would suggest spray foaming the inside of the aluminum tubes. Warm air holds more water vapor because higher temperatures increase the air's capacity to retain moisture. When warm air touches a cold surface, it cools down, lowering its capacity to hold water vapor. If it cools below its dew point, the excess water vapor condenses into liquid on the cold surface.

[@cachecamper]

We find it better to leave a channel for the moisture so that is has somewhere to go when, not if, but when it is created. Those tubes all have a drain to the exterior. Each fastener in the studs, being steel, are going to condense regardless of insulation. The moisture needs to be given a path. The sheer cost to fill each stud is too high and does not yield a great enough benefit. So, it fails the cost to benefit analysis. You also risk "ovaling" out the studs from the foam expansion. The only way to stop that is to drill several relief holes. The cost is too high. The way these are insulated has proven efficient enough leaving no need to go further.

[@sw5334]

@@cachecamperI build aluminum sunroom/solariums in Canada. In the winter we have gas stoves cranking out the heat inside the rooms with exterior temps of -30. Our extrusions are build with thermal breaks extruded in them separating the outside half from the inside half. The wall structures are designed as an internal weep system as it is impossible to fully insulate all the internal cavities. Spray foam are very forbidden inside the walls as they end up trapping all the moisture. Giving the moisture a way out is the only option that has been found. Just like a Land Rover, we don’t build them water tight, we make them drain well.

[@cachecamper]

@sw5334 I love your comment. I'm making this the center point of one of my videos. What is the name of your company? I would love to check it out and learn more about what you do.

[@sw5334]

@@cachecamperthe manufacturer of the product is called ‘4 Seasons Sunrooms’ they are based in the New York area. I’ve been the head installer in the Edmonton Alberta area for close to 20 years. I build each room as a custom build onsite so some have more/less panel/glass. We use sips for roofs and full glass roofs. But each room is 90-95% aluminum and glass so we deal with condensation all the time.

[@mbabcock111]

If you're concerned about moisture inside the aluminum tube then either run a heating wire throughout the frame or fill it with expanding foam.

[@NickA-t2e]

I'm enjoying your videos I just subscribed. Aluminum frames in a cold weather camper kinda suck, but they are a good trade off for the strength needed in the places your customers go. There is no perfect way to avoid the thermal bridging unless you build an additional insulated wood frame inside the aluminum frame. Obviously, that's not cost effective or light weight but may work in some custom build for a extreme situation. I just read all the current comments an I am surprised how many people suggested adding foam inside the aluminum tubes.... That sounds like a logistical nightmare to actually pull off without a very elaborate set up. Plus it won't stop the thermal bridging any way. Thats like eating insulation an expecting it will keep you warm lol. The condensation will still form then be trapped causing even more damage. It's far better to let the frame breath with the vent holes! Same goes for the comment about having the aluminum frame inside the SIP. The camper is going to heat cycle cold to warm many times over its life, and the condensation needs to go somewhere. From what I can see I am very impressed with your build quality! Awsome job; keep the videos coming.

[@clintstinytrailerconversio5560]

I wonder, have wondered, and have seen the interior fasteners to wall posts and ceiling bows sweating and obviously bleeding water into the plywood, and wondered if the said fasteners could be the main cause of the thermal bridging? Aluminum and steel, same-same. Granted there is moisture inside the posts, bows - studs if you prefer, but how much does the fasteners contribute to the effect? And, to take it further does screwless construction lessen heat lose and lessen condensation? I have built-out several cargo trailers / campers and insulated with foam between metal structure (tight, tight tight), added furring strips at right angles (fastened to structure) with yet another layer of foam; then interior plywood fastened independently of the metal structure. There then isn't moisture on the interior fasteners, but I have never ripped one apart to see if there is signs of moisture on the hidden fasteners to the metal structure. There is only so much you can do with these thin walls and with an eye towards keeping weight at a minimum.

[@cachecamper]

The fasteners into the studs are definitely a continued thermal bridge. The benefit of the tube rather than 'Z' or 'hat' studs is that the moisture has a place to be channeled. The entire mission of the box is not solely insulation value. It must be able to be up fitted and have pieces and areas of the unit replaceable over its life span. So this is a good insulation value that solves 90% of the moisture issue while giving a strong structure that will hold up well to off-road tweaking and abuse along with the washboard dirt roads. Cargo trailers were not built to 'not' leak. They were designed to just let the water out. So, when you're building them out with insulation, you need tobcreat channels for water to escape. Otherwise, you get mold and water damage.

[@VTX1029]

If you are providing water channels for the tubes to drain you are also providing a spot for moist air to enter the structure. You're method is a good trade off because keeping the weldment airtight isn't an easy task due to wanting the ability to attach other items to the studs and the likely hood that the weldment would remain airtight over its life cycle. Do some testing with Polyurethane adhesives like Sitkaflex 252 or 3M 500 series adhesives. I bond on 3/4 plywood strips to structures like this so I don't have thermal bridging of the screw to the aluminum stud. The wall sheeting only attaches to the plywood strips. While not as strong as your method it eliminates the thermal bridge of the screws into the stud.

[@bluethunder1951]

I’m not a truck camper builder, but I’ve owned a truck camper (2009 Bigfoot 25C9.4) for ten years now in Canada where the weather is truly challenging for truck camping. Some of the lessons I’ve learned are to keep regular maintenance on all areas where moisture can infiltrate into, lots of chalking around all seams especially on the roof ports. The one thing Ive done after having to replace the wood framing under the door entrance due to poor threshold drainage is to replace the material with composite material and quality sealer material. Other than that I’ve also built an extra high camper port to park it in out of the weather, that by itself has made the maintenance drop off significantly each year. My question is with all the new materials available to build campers with why use materials that eventually degrade over time?

[@cachecamper]

There is no direct answer to that question specifically. Even though it is a really good question, it is one that, once answering, is surprisingly broad. I will make a video on this in time. I need to figure out an articulate way to narrow that down.

[@freedomtowander]

I think I heardthermal bridging contributes to condensation. Plastic fasteners for vapor barrier could help with condensation 3:43

[@samuelfox8126]

Look into spray cork and aerogel paint. Thermal transfer is the lowest of any coating.

[@cyberswept]

As the temperature of the tube's exterior drops, the air inside the tube can reach the dew point (the temperature at which air becomes saturated with moisture and starts to condense). This is what causes "sweating" on the surface of the tubing. If you insulate only the outer surface of the tube, you're preventing condensation from forming on the exterior, but this can shift the condensation problem inside the tube. The insulation on the outside reduces heat transfer, so the temperature difference between the inside and outside of the tube remains, potentially causing the inner surface of the tube (or the air inside) to still reach the dew point and sweat on the aluminum tubing. By inserting closed-cell foam inside the tube-where it makes contact with all sides and fits snugly-you essentially could reduce the area where sweating can occur. Obviously this would have to be done after the structure was welded, so a change in build procedure would likely be in order to accommodate that.. However, for this to be effective, the foam must fit snugly with no air pockets. Air gaps would allow moisture-laden air to remain in contact with the tube’s surface, potentially leading to condensation. The foam should provide a continuous thermal barrier to effectively reduce the sweating effect if you want to go to that route. Mitigation of the moisture is the best you can do. It can't all be entirely eliminated, so the plan would be to manage the moisture to a level where it won't cause harm. Have you ever considered doing a build with 90° Rails or channel? It would naturally produce less condensation, Provided it could maintain the integrity of the build.

[@cachecamper]

Thank you for the comment! I think I'm going to make a part 3 video on this build method to explain a few things further that I did not cover in these two videos. Yes, we have considered channel but always set it aside because, though it is less of of thermal bridge it does not allow a cavity to control where the moisture goes. That is what tube provides. That is whyvwe use tube. We are transferring the moisture to the inside so that we can control where it goes. It works great. I'll make a part 3 video for this one tomorrow.

[@cyberswept]

@@cachecamper right. I watched another one of your videos after commenting and saw that you drill holes so that the moisture does not get trapped. My brother built me a frame out of tube steel for the sides on my flatbed trailer. The first time I drilled into it, a rush of air was released. Amazing the pressure it can build. So I think you are on the right track because your welds are so good, drilling holes near the top and then at the bottom would give some ventilation and relief. Since without the holes it is a closed system, provided the welds are all tight, I wonder if a small ventilation fan could keep it from building condensation. In my motorhome it has the skylight in the bathroom. It has an outer and inner clear cover, so dead air space in between. Of course when you took a hot shower, air space fogged up. When I replaced the skylight, after it had aged and cracked, I created a venting system. It pulls air through a small duct from inside the RV and blows it through an exit duct outside with a flap on it. So far it has worked and the fan works on solar since we camp mostly in the summer. Thinking about the build now, I wish I would have installed a humidity sensor on the fan to turn it on automatically. Anyway, my 2 cents.

[@racebanning6390]

Humble Learning👍👍🏁🏁Im at retirement age, spent 20 years Precision Assembly Technician. In my experience.... Kicked out of work 5 years from retirement. I was forced to live in my truck ever since. I found a 1995 ish Pristine Callen Camper shell. 1 inch Steel frame, R6.5 fibreglass insulation. Aluminum skin. It Rocks But...... Curse the thermal bridging!!! Lol😂🤣Its been up to -10 here in Idaho, and this Old relic has kept me alive. Praise the Lord, but my plan is to remove All the thin ply walls and insulation . Clean , prep all the steel frame, and basically Raptorline the steel and interior exposed aluminum #1 #2 Install 2" inch Rigid pink foamboard like that stuff in yours. Then...... cut 1x1 inch hardwood strips to make up the added 1 inch of insulation foamboard. making my New walls 2". Between the steel and wood strips i am going to use the Eternabond Tape.Its Gnarley, i used it last summer to Re-seal the Callen Camper seams on the roof. It should be a Great Brake between the steel and wood , reducing thermal temp transferring in summer and winter. Then another strip to seal the Insulation board to the woodstrips basically creating a complete interior seal. Then replace my paneling with new stuff. Its been a trooper and it deserves a Resto. Maybe someday You can build me a Newer version of what i have , .. never know. I subscribed so i will watch your progress🙏🙏🙏Be blessed!

[@cachecamper]

That's great! I love hearing about the projects. There's truly no "no way" to do things. There are many good ways to put a product together. It all depends on the mission of the unit. I hope it works out for you and thank you for your feed back and for taking the time to watch!

[@stevecarlisle3323]

If you want to learn about aluminum composite construction, check out how the emergency van bodies like Crestline ambulances are built. Also better foam is what roofers use before torchon.

[@cachecamper]

Interesting. I'll look into those

[@stevecarlisle3323]

@@cachecamper I use Soprema brand 4x8 sheets, 1" thick and up, has fiberglass thin bond one side, and poly resins have no effect on it. I use it for marine deck house construction. 😉🇨🇦

[@tgreening]

My ambo was aluminum construction but as far as I could tell nothing special about it. Aluminum tube frame and a thick-ish aluminum skin. Insulation was either foam, or in my case mostly standard fiberglass batting like you’d find in a house. Interior was just thin wood panels. Strong as Caribbean rum, but nothing special about how it was constructed or insulated

[@stevecarlisle3323]

@tgreening How was the skin attached to the tubing 🤔😉🇨🇦

[@tgreening]

@@stevecarlisle3323 Without tearing it apart, I can’t really say, but I would imagine something similar to sika252. That in itself isn’t anything special since that’s a very common way of bonding habitats. Some people use that, some people use an equivalent tape, some folks will screw or rivet. Different strokes and all that.

[@SpringLake842]

What if you used U channel instead of four sided tubing? You could insert the panel tight into the U and eliminate a large amount of the air/vapor, and still retain a surface for attaching plywood, etc. It would require some work-arounds, but everything is a compromise. Thanks for your video.

[@cachecamper]

@SpringLake842 that's definitely a good idea and one that we have come close to doing many times. The reason that one has gotten side lined, is because moisture always seems to win over the life of any unit. Go figure. When it does win, having a way to control that moisture is the key. So we have found that each tube being left open is the absolute best solution. The life span of the structure goes up while remaining serviceable. So, when a team member smacks into something and damages a panel, or whatever the case is, the cost of repair remains low. The U-channel is difficult to insulate outside of spraying. That's all.

[@jimmyfranklin6927]

Have you sprayed foam in the studs before

[@cachecamper]

This has come to the discussion table many times. But fails the cost to benefit analysis. Though you can do that, the amount of work to do so is not justifiable given the current insulation value has proven to be plenty efficient for the mission of the unit.

[@josephpuchel6497]

How much would it cost to spray foam ? I think it be worth the cost

[@cachecamper]

@josephpuchel6497 if the goal is insulation only, then spray foam makes perfect sense. However, once you take into account the need to replace exterior sheeting for one of many reasons, then spraying falls back down the list. It is a great idea though if you do not see the future need of servicing a panel.

[@lesnewsom6000]

Air is actually a good insulator, but not fresh air…Condensation forms where warm and cold meet if there is any fresh air available. The condensation (moisture) stopped happening close to your studs when you made the foam tight to it because you removed the air gap. As another person posted, you can foam inside the studs. Problem is, you have to fill the void completely because any screw hole will allow fresh air in, leading to moisture/condensation. Replacing the square studs with a Z or U shaped stud would alleviate the issues, reducing your thermal bridging too.

[@cachecamper]

Well put together response. That's one we've tossed around quite a bit. The stud selection. We've stuck with the square tubes for several reasons. Upfitting capability, controlled moisture channel, they hold up best to structural twisting and tweaking over time, and the amount of heat loss and moisture created has not proved to be great enough to make a change. But this sure is more work. So essentially what you're explaining for the moisture is that it is due to the air in the tube being exposed to the "atmosphere", for lack of the right term, and not that it is an air pocket?

[@lesnewsom6000]

@ Yes, ATMOSPHERE” is a good term for it. If you can mitigate that pocket of air, you will solve the condensation issue. I understand the need to stick with the square tubing. One possible solution is low-expansion foam to fill the void. One other thought comes to mind, and that is the expansion/contraction rate of the aluminum structure. The foam board being tight against the stud solves the condensation issue but introduces a concern for wall integrity when the rigid foam board is under compression. I am not an engineer and do not know if it would be bad or not or if it would get worse over time. If it were an issue, using a softer foam, like polystyrene (the white ball stuff) to picture frame around the rigid foam would work. Though a bit laborious, it would allow things to move/expand/contract while also maintaining a tight connection between the stud and the insulation. Hope this all makes sense and is helpful.

[@robertdoyle8972]

I worked for interior weatherization in Fairbainks Alaska for eight years and you should look up energy out west conference and maybe look at going to one of them and I do have infrared cameras that you can use if you want and I would love to come by and check out your factory

[@cachecamper]

Interesting. You're welcome to come visit. You said Energy Out West conference?

[@robertdoyle8972]

@ yes would love to come and visit and yes energy out west if you look it up it will let you know when and where the next conference is and you can see what classes they will be offering I use to go to all of them

[@MN_Doughboy]

Aluminum does NOT cause moisture in the wall. Aluminum may cause condensation. But the moisture is already present in the air.

[@randallcash2334]

Condensation All air has water vapor in it It is like a glass upside down creates water

[@jerrytalley802]

It seems pretty simple. Warm air inside, hits the cooler metal, the moisture form, just like any other place warm and cool air collide.

[@nesbitttom]

The wet center of the aluminum tube is caused because the aluminum is cold and the warm moist air from inside the campe is leaking inside the cold tube and condencing. Thats the why its happening. Heres my suggestioto stop it from happening.. Insulate the out side of the camper, move the layer of insulation from the inside to the outside, now you are stopping the cold thermal bridge before it gets to the aluminum , allow the aluminum to be apart of the inside conditioned space, allow and promote the alluminum to warm insted of trying to sepreate it from the warm try to seperate it from the cold. In the housing industry Its considered EIFS Exteriour Insulation Finishing Systems

[@alanfoix9911]

Try building the frame inside. 😊

[@floriotj]

I'll explain what I've learn about this subject of vapor barriers which may be only partially or possibly totally incorrect and for full disclosure I'm not an engineer. What you're trying to mitigate is moisture being trapped inside your walls because of the difference in temperature between the outside temperature and the inside temperature. As we all know the reason we want to do this because moisture in the wall cavity causes material(s) damage and let's mold grow. Here's the two things you need to know to understand what happens. First, warm can hold way more water (as a vapor) than cold air. Second, what happens when you have a surface where it's cold on one side and warm on the other the warm air with lots of moisture contacts that surface which has been cooled by the cold air on the opposing side. The temperature of the warm air cools and reaches dew point there by condensing on that surface. In simple terms the vapor barrier is to control where that condensation occurs. Also, think of insulation this way. Insulation isn't to keep cold air out, it's to keep warm air in. If you have enough warm air and insulation to keep you warm in a sealed environment where the warm air can't escape easily a piece of 6 mil plastic will work as a vapor barrier as long as it installed in a way that keeps the moisture out of the wall cavity. Really all you're trying to do is keep the moisture from getting into the wall cavity and causing damage. It really is that simple. Exterior "house wrap" such as Tyvek serve a similar role in wall construction with the primary difference being they won't let moisture in but they will let moisture out. I think exterior house wraps are a good choice for exterior wall surfaces even on camper and trailer wall systems but again I'M NOT AN ENGINEER. Any penetration you make in a wall whether it's a door, a window, a vent, a rivet or a fastener of some kind must be designed and installed so moisture can't get into the wall cavity. Even with a well designed wall system incorporating vapor barriers and related moisture protection "weep holes" should be used to allow inevitable moisture that will migrate into your wall cavity to escape the wall cavity. Compared to many other camper wall systems I've seen I like the Cache Camper wall system with the exception (I'm not an engineer) it lacks a proper vapor barrier system both internally and externally. It does have a good thermal bridging system with the 1/2" foam on the inside wall but should have plastic between the plywood and the 1/2" foam. The way I see it is this simple; HEAT FLOWS TO COLD - ALWAYS. Your wall system should do two things. Stop your heat from flowing to cold and stop moisture from getting into the wall system from either the interior or exterior. Then add some strategically placed "weep holes" as insurance.

[@setheroth28092]

I’ve never built a camper, and never studied thermodynamics or physics in school. I’m one of those KZbin Armchair scientists. Condensation happens when air containing water becomes too cold to hold the water it contains. If water condenses inside the aluminum frame, it means there is temperature changes happening there (likely due more to exterior day/night cycles than interior thermostat changes). So during the day the frame warms up and allows humidity to come in, then at night the frame cools down and the humidity condenses inside. Perhaps filling the frame with expanding foam would keep air out of the frame and fix the condensation problem at the source?

[@cachecamper]

You could, but the cost to benefit analysis doesn't pencil out. In our application, it's better to just leave it as a channel for moisture to be controlled. The number of relief holes that would need drilled in the studs to stop the tube from "ovaling" out would take so much time and yield little benefit.

[@einarquay]

Use pressure treated plywood. Your goal is to prevent rot, for twenty years. . 🎉 Moisture can only occur in the structural aluminum boxes if the welds are not continuous. No condensation can occur where no vapour transfer can occur into interstitial spaces. Those two measures will provide a cure for 20 years. Also, you do not need a thermal break, these aren’t houses. There is a reason that Airtreams last a long time,

[@cachecamper]

Unfortunately, pressure treated plywood causes significant oxidation on aluminum sheet metal and aluminum in general, once salt and or calcium cloride is brought into the equation. Those who understand the chemicals used in the pressure treating process can comment on that. You need to allow moisture to have a path and the inside of the tube is the best place for that.

[@einarquay]

@ you seem to have made up your mind on these matters, despite asking advice from knowledgeable commenters. Good luck. Yes I do know that copper and aluminum reacted when in contact. The solution is to separate the two materials with a butyl barrier and use stainless steel screws. There is no value in you tacking solutions to imaginary problems for building an RV . They are disposable commodities. Keep it simple.

[@cachecamper]

@einarquay always open to conversation. We used to use a great deal of pressure treated and galvanized metal in our building until proved to multiply the corrosion problems even when separated with various thin barriers. Once moisture got involved, the existing materials just took over and would fight everytime. We put 5 year Warranties on our builds so we had to take treated and galvy out. Now I will say, we still use treated in a couple of areas. Just not here.

[@P_RO_]

If you read the stickers, spec sheets, and such for any treated wood they prohibit direct contact with aluminum because of corrosion problems. Those same chemicals will also eat away any non-stainless fasteners.

[@einarquay]

@@cachecamper good. See how it goes. Product development is iterative.

[@P_RO_]

Your approaches seem to be based on empirical evidence rather than direct application of scientific theories. IMHO that's a better approach because many things do not do as well in real-world conditions as they are predicted to perform in theory. Experience over data because it's not about how it's supposed to work- it's about how it actually works. You can greatly increase the load-bearing ability of structural panels by bonding the load-bearing element to the skin instead of only relying on through-bolting where only the bolt contact with the skins carries the load. Done properly even 1/4" plywood can carry surprising loads. Concentrated stresses fail easier than distributed stresses- that's a basic engineering principle.

[@cachecamper]

This is all true. It is very good to base things on scientific data, though. This is actually an interesting point because if I invited a scientist, mechanical engineer, a process engineer, a repair expert for all these methods and the client to the table, and looked back at all the past structures and failures and then at this method, we would essentially land on this. Or something close. There are improvements that can always be made, and we're always improving every model.

[@P_RO_]

@@cachecamper If you invited all those people, the client would walk away due to all the bickering over the details. Find what works and until something is proven better in use stay with it.

[@markbajus7132]

just a thought, residential building science has moved to heavy insulation on the COLD side. that would keep the aluminum studs warmer minimizing the condensation issue. PERMIABLE vapour barrier both sides to control, not trap, any water vapour. think about it this way as an exaggerated explanation, if you had a piece of aluminum tube just sitting around inside the warm camper, there would never be any condensation regardless of humidity inside the camper because there is no temperature differential to create the environment for condensation. The insulation on the outside moves the dew point out into the insulation layer, not the stud. This of course ignores any practical building issues this might create!

[@cachecamper]

@P_RO_ 🤣 that is incredibly true! Hahaha

[@cachecamper]

@markbajus7132 excellent comment! What you said there at the end is the most annoying reality that seems to win in most cases. I am currently brainstorming like crazy how to get that thermal break layer moved to the exterior while maintaining reasonable cost. The issue is that it just won't hold up over time. So, I'll continue brainstorming.