Interior Walls: Aluminum or FRP?

[Rustic313]

Hello,

I am planning my next conversion and wanted to ask for input from those who have "BTDT..." For interior walls, what material works better -- aluminum or fiberglass panels (like "Kemlite"?).

I want something that is immune to rot in my nice new aluminum trailer, and lighter than plywood.

Aluminum
- Pros: Can be installed at the factory with R-5 insulation (less work for me), slightly lighter at ~16 lbs/panel
- Cons: Only comes in white, small dents show very easily, I'm worried about the thermal bridge from alum skin to metal stud to alum interior wall leading to condensation and other issues.

FRP
- Pros: Comes in variety of shades and textures, I can install higher quality poly-iso insulation and seal around the edges (R-6).
- Cons: Slightly heavier (~20 lbs/panel), potential issues above 130 degrees (can see a trailer interior getting above that if stored in direct sun), I will have to do the install myself.
- Unsure: R-Value is about 0.255 for a 0.09" panel... Likely better than aluminum but pretty negligible. May stop the thermal bridge effect.


Cost is slightly higher for aluminum but not a show stopper, especially considering the labor saved by having the factory do it.

Does anyone have any experience working with these for interior walls? Thanks!

[John61CT]

You're absolutely right about the thermal bridging, but that should be eliminated by your insulation technique regardless of inner skin.

Only way to get that job done right is do it yourself or hire specialist pro$.

I would find aluminum too cold in any case, but plastic is hardly better, not talking temperature either.

No way even a nice wood skin should ever rot if you do it right, keep everything easily removable for inspections alterations & repairs. Luan and a nice marine quality finish sure will be more pleasant and comfortable IMO.

[Rustic313]

You're absolutely right about the thermal bridging, but that should be eliminated by your insulation technique regardless of inner skin.

The current gameplan is just to squeeze 1" polyiso insulation between the studs and then seal cracks/edges with foam and/or caulk. We have a 7' wide and want to be able to fit a queen sideways, so I don't think I can afford to put a layer of furring strips between the studs and the panels and still fit the bed. So the studs will likely be in direct contact with the inner skin.

Plus if I go alum I will likely just have the factory insulate and install, and I strongly suspect they aren't going to use furring strips either.

Thanks for the info!

[Dano-Mich]

I put a queen in our 7x12 sideways across the back as well and it just squeezes in. Ours is just under 80" with 3/8" plywood on the walls. We camp in cold weather so aluminum would not work for us - we would stick to the walls! We put 1" insulation between the 1" studs and taped them to seal up cracks. Camped in temps below -12F with electric heater on low and kids were still too hot up on the bunks.

Would you have anything under the aluminum or FRP? Seems like the walls would be very easy to dent (aluminum) or break (FRP) without a backer board of some sort. Curious what others have done, subscribing.

[John61CT]

If it were me I'd do not just between the studs but a full envelope over them, at least a half inch of course more ideally.

Even if it meant slicing a bit off the foot of the foam mattress.

And thanks for the reminder to buy 7'6" interior width when the time comes.

[aggie79]

I wonder if the manufacturer would be willing to use ACM (aluminum composite material)? While it won’t eliminate all of the thermal bridging, the polyethylene core between the two aluminum sheets should be better than aluminum or FRP. The rigidity of the ACM would also eliminate the need for a backer ply.


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[Rustic313]

After a little research I came across this:
http://parklandplastics.com/product/duro-therm-3/
https://www.menards.com/main/paint/pane ... 27&ipos=13

A little spendy ($39.99 at Menard's) but its 5/16" thick (rather than the 1/10" of most FRP panels) so it likely has some structure to it, and it offers an R-Value of R-3/inch (so R-1.5 for the panel). It weighs 0.4 psf, which compares well against aluminum (about 0.43 psf) and 3/8" ply (around 1 psf).

It may need to be painted for aesthetics so the inside doesn't look like the freezer section at the grocery store but that should be do-able.

[PrecisionLook612]

If it were me I'd do not just between the studs but a full envelope over them, at least a half inch of course more ideally.

Even if it meant slicing a bit off the foot of the foam mattress.

And thanks for the reminder to buy 7'6" interior width when the time comes.

Depending on your height you could also order a short Queen which is 75" long vs a regular queen at 80"

[John61CT]

Yes a couple inches more insulation you could make it well comfortable with minimum fuel use even in extreme temps.

That plastic looks like just the ticket for lining the inside of a custom fridge box without doing custom fiberglass, wonder how strong it is against punctures?