insulating bare aluminum skin and tube frame

[ssuuki19]

I am posting in this board because it was suggested and I need to pitch this idea somewhere for feedback before I insulate. The shell is 16 gauge aluminum (thats .051" for alumimum) on 1" square tube aluminum (.125" thick), you can see my build thread for relevant pictures. But the point is all those thermal bridges, ceiling and floor spars included, and condensation and dew point graphs and all that moisture stuff. Here's my idea, and all there is is aluminum and sikkasealant so thats a good waterproof start:
-1/2" layer closed cell spray foam on the frame layer
-then wiring done in the 1/2" (approx, or less) air cell gap and through the 1" aluminum framing
-then 1 1/2" of open cell acoustic insulation semi-rigid foam on top of the frame layer (entire envolope, floor to ceiling covering all the frame thermal bridges)
-then 1/8" plywood (cork composite t&g on floor)

So this would have an air space behind the open cell foam, but before the xps foam, but is this ok? To use both? Here's my reasoning - cold aluminum will attract condensation so put xps right on it in a thin layer forcing any condensing moisture to enter the eps foam layer (to breathe out in the morning) instead of forcing it to the frame.. and I guess to the floor with gravity. I know this happens with wood, it would be worse with aluminum I reckon. (hope I'm explaining enough so you get the picture) Now thats why there is a closed cell foam layer 'behind' the acoustic insulation layer. Call it xps/air/eps/alumized film/vinyl/eps/plywood because thats the 1" + 1 1/2" + 1/8" sandwich. 2 and 5/8ths everywhere. (if i have left overs i'll put it on the ceiling)

You cargo trailer conversion folks have probably had to make similar decisions on how to insulate with aluminum and thermal bridging so looking for some feedback, so please share with me your experiences/recommendations, etc. This prototype trailer needs some guidance to continue its build.

[greygoos]

There is a previous all aluminum tear on here an the insulation process is explained. viewtopic.php?t=51991

[CoventryKid]

If you care to, check my build (link below) to see how how I insulated my 7x16x7 v-nose all aluminum NEO CT.

My wife and I have been full-timing in it for 17 months now and have had NO problems with condensation.

We've experienced 101F temps on the US east coast and cold and snow on southern Vancouver Island this past winter.

Hope this helps.

[ssuuki19]

There is a previous all aluminum tear on here an the insulation process is explained. viewtopic.php?t=51991

Yes thx, I'm familiar with the Northern Lite thread - in fact at the start of my (pre) build thread I got input from that builder, Fred, on my setup. Was just seeing what else is out there for research purposes. Definitely will read that thread again though, thx, greygoos.

[fourbtgait]

So are you concerned with the interior of the tubing not being insulated?
Or the thermal bridging of each side wall thickness of the tubing when the center of the tube has been filled with foam?
If the first, then simply fill the tubing with expanding foam.
If the second, I myself would not worry of the thermal bridging presented by the tubing wall thickness.

[ssuuki19]

The 1" square tube 6061 .125" aluminum is the frame. Think of it like 1x1 wood.. the wood frame is 1" thick, that 1" envelope of the entire trailer is the first part of my problem, so what you are saying is close. If you can see that 1" layer insulated still the tubular aluminum frame (or 1x1 wood frame) still a gigantic thermal bridge, aluminum is way worse than wood for thermal bridges because of its properties compared to wood. Within 'that envelope' there is a 1'5" layer of open cell foam to cover the entire body of the frame (except the l-track and the other required thermal bridges that cannot be avoided). Does that make a good sense, I should make a picture.

[Padilen]

So are you concerned with the interior of the tubing not being insulated?<br />Or the thermal bridging of each side wall thickness of the tubing when the center of the tube has been filled with foam?<br />If the first, then simply fill the tubing with expanding foam.<br />If the second, I myself would not worry of the thermal bridging presented by the tubing wall thickness.
Has anyone actually filled the tubes? What was used ?

Sent from my XT1635-01 using Tapatalk

[fourbtgait]

Simply insulate the interior of the tubes.

[Padilen]

Simply insulate the interior of the tubes.
So you've done this how?


Sent from my XT1635-01 using Tapatalk

[fourbtgait]

Quick and dirty.
Example;
Buy a can of foam.
Measure diameter of straw on can.
Measure length of straw on can.
Drill a hole slightly larger than dia of straw. Spaceing will depend on experimentation.
Feed straw thru hole, down inside tube. Pull back out as you spray foam.
Then feed tube opposite direction from same hole.
Depending upon expansion rates of foam, it will be constrained by the tubing and expand longitudally.

[fourbtgait]

I assumed, maybe wrongly, that all of the ctc have had tubes and/or channels filled with foam the same way. My walls are z channel, but roof and nose bows are c channel and will be foam filled.
You can use the same method to fill the lid of an ice chest which unless you spend big bucks, have no foam in them.

[Padilen]

So I'm assuming since you said Example, you've not actually successfully done it. I have tried to use spray foam to fill things and I found: it expands like you'd expect, then collapses into goo. Maybe my testing methods or "great stuff weren't good.. I'm sure that there is some that expand more & "fill bigger gaps" but I would wonder if with those, if rupturing the tube or distorting it would be possible. If there is a proven method, and type of insulation, someone please share.

Sent from my XT1635-01 using Tapatalk

[fourbtgait]

So I'm assuming since you said Example, you've not actually successfully done it. I have tried to use spray foam to fill things and I found: it expands like you'd expect, then collapses into goo. Maybe my testing methods or "great stuff weren't good.. I'm sure that there is some that expand more & "fill bigger gaps" but I would wonder if with those, if rupturing the tube or distorting it would be possible. If there is a proven method, and type of insulation, someone please share.

Sent from my XT1635-01 using Tapatalk

Lol, I used the word example as to give you an example. Yes, I have done it. Yes, its messy. Yes, with the wrong foam it will expand and rupture or distort a member, or distort the aluminum skin on a c channel.
Funniest thing I saw was a guy mix up a 2 part foam to fill the bilge of a fiberglass boat, flotation and sound deadening. Except it distorted the hull, broke the deck loose from the hull as it expanded.
I see that they are marketing foam delivered in a tube thru holes cut in siding or drywall to insulate existing houses. No distortion of the drywall.

[Padilen]

I'm not willing to risk goo or distorting my CTC. I'd also think the number of holes needed even as small as possible could weaken the tubes. The idea of foam filled tubes I like. Until there is a complete how to, complete with video and materials list, I'll pass.

Sent from my XT1635-01 using Tapatalk

[fourbtgait]

Insulated roof bows.
6 bows, 5 cans non-bowing great stuff, plus misc gaps to use up last bit in cans.
I thought of doing a pvc pipe as a test, but why, when my ct had 1" holes drilled in two of the roof bows when they installed two lights. So I found a 3' section of vacumn line that fit over the straw of the foam can. I fed the hose down to the curve of the bow, started slowly filling and pulling hose back out. I can hear the foam in the tube, had empty screw holes ocassionally to gauge filling. Got to the center, reinserted hose to fill the other side of bow same way. It did not make it all the way down into the curve of the bow, so drilled a 5/16 hole there and fed the straw up and down to fill it.
Is it 100% foam filled? Doubtful, but only destructive testing would show. I would be satisfied with 50% filling rate, better than zero. Roof skin distortion? None as the foam is designed not to.
Clean up of straws and hose with acetone allows resuse of all. I still have 3 never used straws.