Plastic or other moisture barrier on steel van floor?

[GreyDawg]

Hi --

Today I am cutting and fitting the unfaced synthetic fiber insulation for the van floor. I have four options:

1) fiber insulation directly on the steel floor
2) fiber insulation on a 0.7mil sheet of plastic (painter's dropcloth!) on the steel floor
3) fiber insulation on a radiant barrier film (foil on one face, kraft paper on the other) -- roll left from a house insulation project
4) fiber insulation directly on the steel floor, and plastic dropcloth between the insulation and the plywood.

The objective is to keep the steel floor from developing rust from condensation.

Thoughts about which solution to pick?

Thanks,

[WVvan]

Don't use fiber insulation on the floor. It's the air in between the fibers that gives it any insulating properties. The puffier the better. If you put it on the floor it will be flattened, ie no air giving insulation. If you are going to use insulation use the rigid kind. The air is trapped inside the foam. It will probably still flatten out some when used on the floor but not near as bad as fiber.

Condensation is caused by moist air which tends to raise. The moisture problems will be on the walls and ceiling. Of course the water could drain off the walls onto the floor but that's a different issue.

Use the fiber on the walls or ceiling where it won't flatten.

[spurious]

Check out other cars Mercedes etc. All use a Jute sound deadning material(It is not Fiberglass based, but a wool and cotton blend). The idea is if there is moisture it is able to breath out in time. That is also why you don't want plastic it will not allow it to breath and trap natural moisture between metal and plastic resulting in rust.

Jute also comes in foil backed, and in various weights.

[zippy]

So, what's the solution to a vapor barrier?

Also, is there some kind of insulating subfloor that would works well in this type of van?

[12bproper]

just an idea, install a dehumidifier???

[scatter]

I'd check into this outfit. I've been very happy with their products.
www.quietride.com
Very complete kits and fit like a dream.

[campervanbeethoven]

I wouldn't put any thing between the steel and your subfloor. use marine grade 3/4 ply for subfloor and then add your insulation on top. I just relied on 1/2 inch capet padding and a nice nylon carpet. works ok, if you want somthing more substantial fir on top of the subfloor (16" centers) and lay blue foam insulation of desired thickness between fir strips. (ie 1" or 2") then add another layer of plywood. This time just use cheap cdx. 5/8" would be plenty. this will produce a well insulated floor with the abillity to breathe. if you go with the sandwich style floor you can use 1/4" marine plywood on the bottom instead of 3/4" and gain a half inch of head room.