Insulation Under The Floor

[MtnDon]

A question for those you have installed rigid foam insulation under the floor, between the frame rails. In particular those who glued/secured it in place and did not cover the bottom side with anything. I know there are a couple out there at least. I would like to know how it has stood up to a few years of towing. Has road debris had a bad effect? Thanks

DonM

[Martiangod]

I would cover it, will last much better, coroplast is cheap and works awesome for that

[tony.latham]

Don:

I can't answer your question since my floor is a sandwiched .5" ply/.75" foam/.25" ply on the bottom. I put the foam in to stiffen the panel and perhaps keep condensation out, even though the entire construction is sealed. And of course I wanted an insulated floor.

But here's my point; In my situation, all of my floor is now covered by 5" of foam mattress and a 2" memory foam topper. Why would I need any insulation down in my floor with all that foam on top?

I wanted a nice thick floor for structural reasons. My sandwiched walls sit on the floor and overlap and the floor thickness gave me something to glue and screw the overlapping exterior wall to. Plus the foam core stiffened up the 1/2" ply so it doesn't flex, even when I was walking on it during the construction phase. I'd probably do it the same way, but not for insulation reasons.

I hope this helps.

TL

p.s. my 1/4" plywood on the bottom is subfloor ply that was cheaper than 1/4" CDX and a much better grade of plywood –no interior voids and rated for "moist environments."

[MtnDon]

Talking cargo trailer floor, not TD. I should have mentioned that. The bed would be raised off floor and there would be standing room, hence the desire for floor insulation. Also do not want to insulate on top of floor, inside trailer, as that reduces the headroom to the slouch zone (foam sheets added to ceiling on inside will take away enough).

Thanks DonM

[bc toys]

I'm on my 3rd cargo and never insolated the floors, wall and ceilings yes but I'm in Nevada 68* today

[Roly Nelson]

Ten years ago, before I knew anything about teardrop floors or insulation, I installed R-19 fiberglass insulation below the floor and then added a layer of 1/4 inch plywood below it to keep it in place..........Big mistake! This sealed area was a perfect place for unwanted moisture, or any water due to any leaks in the galley or galley hinge. Since then, I have hopefully solved a potential problem, by drilling vent holes in the TD floor, below the mattress. I agree with a previous post, that no insulation is needed, since the mattress does the same job, probably even better. My other teardrops simply have roofing pitch on the bottom of the floor plywood, and seem to work just fine. Good luck on your build, remember ask questions, we are here to help.
Roly, the li'l ol' Woody TD builder in So Calif

[Tinbasher]

I plan to insulate my floor because I don't want the Hot / Cold interface to be between the mattress and the floor leading to potential damp in the mattress. Also rigid foam adds a significant degree of stiffness to a sandwich floor that soft Rockwool type or no insulation doesn't.

Ultimately I guess it depends where you plan to use it and the prevalent weather. In Northern Europe even in summer I think it will be be of benefit in reducing or at least controlling where condensation occurs.

[aggie79]

I plan to insulate my floor because I don't want the Hot / Cold interface to be between the mattress and the floor leading to potential damp in the mattress.

This is the reason I chose to insulate my floor. I've read that in damp climates or marine applications, a design consideration is to elevate the mattress so air can circulate below it to reduce the dampness potential.

Roly mentioned that he drilled holes in the interior side of his floor to allow condensation to be able to evaporate. While I used closed cell insulation instead of batt insulation, I did leave the interior plywood skin unfinished to allow water vapor to dissipate. (The exterior plywood skin is sealed with epoxy and rubberized undercoating.)

[MtnDon]

I had forgotten about the coroplast being used to skin over the underside to protect from rocks, etc. That sounds like a good idea and there is a local supplier with full sheets available too.

I definitely want insulation against high heat (SW USA) and cold (CO, ID).


Note that if the plywood is rated, exterior or exterior, exposure 1, the adhesives used are waterproof and the plywood will not allow pass through of water or water vapor. Plywood rated exterior, exposure 2 has an intermediate type of glue; may not be as waterproof. Interior2 marked plywood has no water resistance and would probably pass water vapor.

[aggie79]

The plywood I used is Russian birch. It is an interior plywood but I can't recall its markings. I'm pretty sure it is vapor permeable.

[MtnDon]

Most plywoods that have "nice" veneers are interior only grade.