Question about using foam in the floor...

[mdk]

I'm thinking abut the idea of insulating the floor by using a combination of plywood, 2 (or 4) inch foam, and plywood. The trailer's frame currently has bars crossways every three feet or so, but that's all that's there. No end to end "runs", except for the rails the suspension is connected to. I could probably get some angle added to beef up the floor, but instead of adding just weight, I'd rather add insulation...

How thick of plywood would I need to have adequate floor strength? I'm 300 lbs and thinking that jumping up and down on one layer of 1/2 plywood would result in a crash. The main rails are about 5 feet apart (give or take a little) and the metal supports across between them are about 3 feet.

I was thinking of doing something more like using some glued up hardwood plywood lengthwise inside the foam / ply sandwich every 12 or 16 inches or so. Unless of course, some 1/4 on the bottom and 1/2 on the top would be rigid and strong enough.

[atahoekid]

I think the issue you would have is the structural strength for the floor, but that should be an easy fix. Build a wood box frame with runners running nose to tail and left to right that would fit over the trailer frame. You could probably get away with 1x4 lumber on edge, maybe 16" to 24" on centers, since there is already a steel frame under that. Insert foam into the voids then place 1/2" ply over that. You'll want to waterproof the heck out of the wooden box frame and floor (refer to the waterproofing wood sticky) since wood rot is one of the reasons a lot of us came to the foamie side. Hopefully, that idea helps... Maybe others have different ideas, but that's how I would try it. Steel is obviously structurally stronger, but you would pay a price in weight

[mdk]

I think the issue you would have is the structural strength for the floor, but that should be an easy fix. Build a wood box frame with runners running nose to tail and left to right that would fit over the trailer frame. You could probably get away with 1x4 lumber on edge, maybe 16" to 24" on centers, since there is already a steel frame under that. Insert foam into the voids then place 1/2" ply over that. You'll want to waterproof the heck out of the wooden box frame and floor (refer to the waterproofing wood sticky) since wood rot is one of the reasons a lot of us came to the foamie side. Hopefully, that idea helps... Maybe others have different ideas, but that's how I would try it. Steel is obviously structurally stronger, but you would pay a price in weight

Do you think if I added crossmembers at 16 inches or less, I could get away without the 1 or 2 x 4 lumber? I'm not paranoid about the weight, it's just I'm concerned about how spongy the floor would be, along with whether it's actually strong enough to keep me and another person from falling through...

Oh, yes, good point about the waterproofing... That was a given, but thanks for the reminder. Some RV's have untreated plywood facing down, and it rots... Seen it.

[Wobbly Wheels]

FWIW, my trailer's got two longitudinal (1X3 tube) runners 48" apart. There are angle spreaders every 3'. My floor is 3/8 on the bottom, then 1" foam, then 1/8...all stuck together with epoxy and a bit pf PL300.
I'm 265# and there's no deflection.

[Larry C]

http://www.tnttt.com/viewtopic.php?f=50&t=35852

I built my 5X8 floor with 1"X 1-1/8" framing, foam between, and skinned w/1/8" ply both sides, and then glassed with 3oz. Check the link for pictures. This floor is self supporting, the chassis is minimal.

Larry C

[linuxmanxxx]

I've built 3 now with .5 luan on upper and lower and 3/4" foam cut to fit between 1x2 lattice spaced at offsetting 18" and 12" centers with cross members matching trailer rails to bolt through and at finished thickness of 1 1/8" I can walk on it with no problems. I use water based 3M 30NF glue to bond the ply to the foam to get the strength.

The strength comes from using a complete skin on both sides glued and the glue combined with the core being glued to both sides prevents the skin from moving any side to side and with such a large space makes the incredible strength because the load is spread over the entire surface of both sides of the floor. I also use the same methods for walls and double it to 1 1/2" 1x2 flipped vertical on the roof to prevent sagging and it builds a massively strong enclosure.

[mdk]

FWIW, my trailer's got two longitudinal (1X3 tube) runners 48" apart. There are angle spreaders every 3'. My floor is 3/8 on the bottom, then 1" foam, then 1/8...all stuck together with epoxy and a bit pf PL300.
I'm 265# and there's no deflection.

That's pretty light and to have no deflection with 3 feet between supports... Seems impressive to me!

[mdk]

As I was estimating materials today, I suddenly realized that there was going to be a need to put in quite a bit of strength in the floor. My frame, unlike most, does not extend past the wheels.. the original owner removed it. So, I will have to use quite a bit of reinforcement, since the outside 12 inches of the floor on each side will be holding up the walls and roof!

I wish I had been able to start with the frame of my own design, but that's water under the bridge. I have what I have, and it's too good of a deal to backtrack now.

[linuxmanxxx]

In another thread we were talking about extending beyond the from and using angle extensions but if you have enough wheel clearance just build a subframe that extends beyond the trailer with like 2x2 or 2x3 cross braces the width of your floor plan. It's what I did on my first build and actually my extensions were all built from 1x4 just enough of them to spread the load.