rv floor vapor barrier

[Mako_Kupo]

hey guys, I'm about to put on my Class C floor frame which is finally rebuilt. my questions is this:
-Ill be using spray foam insulation, and as of now I am going to use decor leveling sealant between the PVC coated aluminum and the trucks steel frame. then, ill use proflex around the edges of it for a final seal. I've been told by a few people that closed cell foam acts as insulation and vapor barrier, is this true?
-currently, I planned to just sandwich the PVC coated aluminum between the subfloor framing, and the truck steel frame with spray foam doing all of the vapor barrier-ing.
-do I need to put plastic in for vapor barrier? I'm thinking of putting a bunch of noctua 12v PC fans under the floor with the wood, to be running at the flip of a switch to circulate air and vent humidity out of the subfloor. sounds nuts, but its a super easy install and I'm terrified of the floor rotting again.
-will the dicor leveling sealant+pvc aluminum+proflex be sufficient with spray foam? thank you!

[Mako_Kupo]

westend wrote:
Typically, vapor barriers are placed toward the inside of a living structure. This is to stop any moisture from the interior. Since you will have a clad aluminum exterior to your floor and foam between floor joists, a vapor barrier isn't needed.

My 46 yr old trailer has an exterior clad floor system with wood joists and plywood subfloor. While insulating and inspecting the floor system (pulled off subfloor), I found that all of the frame and the subfloor were in excellent condition.

thank you thank you ❤️

I am "recladding" it myself with pvc coated aluminum and alumirbond to seal the seams(between pieces) on the outside, which are overlapping. between the aluminum and the steel frame I'm sandwiching butyl tape where the staples and bolts go through the subfloor and the steel frame. along the (final)seams, ill be using proflex geocel for RVs. between there alumirbond, butyl tape, and the proper trim(which I still need to source and purchase)

is it enough? I don't know how good alumirbond is, but I do know how to use it properly and when done right, its supposed to be "strong as steel" so it should be a strong seam holder. thank you!

[westend]

Typically, vapor barriers are placed toward the inside of a living structure. This is to stop any moisture from the interior. Since you will have a clad aluminum exterior to your floor and foam between floor joists, a vapor barrier isn't needed.

My 46 yr old trailer has an exterior clad floor system with wood joists and plywood subfloor. While insulating and inspecting the floor system (pulled off subfloor), I found that all of the frame and the subfloor were in excellent condition.

[gbopp]

newman fulltimer wrote:

ScottG wrote:
In the southern states where people have houses on stilts that can get water damage during storms, they seal the bottom of the bare wood structure with foam. It can then be submerged without issue because it's 100% water tight.
So if you spray the bottom, you can leave it open to road spray without worry.

no we do that so the house will float once water got high enough :B

We do it so the house doesn't freeze when the weather gets cold enough. :M

[Mako_Kupo]

so I think for the floor ill go in this order, truck frame, aluminum flashing, plastic, wood frame. or should the flashing and plastic be reversed? thanks! (no room for foam under)

[newman_fulltime]

ScottG wrote:
In the southern states where people have houses on stilts that can get water damage during storms, they seal the bottom of the bare wood structure with foam. It can then be submerged without issue because it's 100% water tight.
So if you spray the bottom, you can leave it open to road spray without worry.

no we do that so the house will float once water got high enough :B

[ScottG]

In the southern states where people have houses on stilts that can get water damage during storms, they seal the bottom of the bare wood structure with foam. It can then be submerged without issue because it's 100% water tight.
So if you spray the bottom, you can leave it open to road spray without worry.

[Mako_Kupo]

okay thanks. I wanted to use it on the floor at the very least, because there is no underbelly fabric or anything like that. its direct road to aluminum flashing exposure, so I wanted to put it wherever its supposed to go. does it go between the frame and flashing, or outside of all of it to keep the water away from the flashing itself

[ScottG]

Closed cell is an absolute vapor barrier. Adding more is a waste of money.

[newman_fulltime]

just use a good marine grade plywood it will outlast you