Foam on the floor..

[mdk]

Assuming there's a frame that braces the floor well, how thick of plywood would you need on a standing height trailer if the floor were foam skinned on the top and bottom with plywood? Would 1/4 or 3/8 on the top and 1/4 on the bottom be adequate? Or even 1/4 and 1/4?

[MtnDon]

what is the span between support framework and what size is the framing?

[mdk]

what is the span between support framework and what size is the framing?

That's up for discussion. The span is important, obviously, and it could be whatever it needs to be as the frame design will be determined by what is set on it.

I'm more interested in making sure I won't punch through it with shoes or dropping a frying pan.

[kayakdlk]

For my 5'x10' floor I used 1"x3" pine board laid flat for my frame with spans of about 24" to align with my trailer frame cross members. I then use 3/4 foam between the voids and skinned with 1/8" Baltic Birch top and bottom, using PL premium glue troweled evenly over wood frame and foam. It was very solid and I could kneel or stand on it (approx 200 lbs). The foam glued between the plywood stiffens up the whole panel. Quarter inch plywood would be more than enough. Inside you will be on mattress so the weight is spread out.

Dan

[mdk]

For my 5'x10' floor I used 1"x3" pine board laid flat for my frame with spans of about 24" to align with my trailer frame cross members. I then use 3/4 foam between the voids and skinned with 1/8" Baltic Birch top and bottom, using PL premium glue troweled evenly over wood frame and foam. It was very solid and I could kneel or stand on it (approx 200 lbs). The foam glued between the plywood stiffens up the whole panel. Quarter inch plywood would be more than enough. Inside you will be on mattress so the weight is spread out.

Dan

This is going to be a travel trailer, not a teardrop. So, it will be stood on and walked on, etc, etc.

[atahoekid]

I'd say part of that question is the foam thickness but skinned foam is surprisinglly rigid. Mosts single ply floors are 3/4". i'd feel pretty comfortable with 1/4" sandwiching 3/4" foam core. You can always run a test to make sure!!

[MtnDon]

Rigid sheet foams all have a pounds per square inch rating. The blue and pink XPS foams are generally 15 PSI but the are 25 PSI as well; polyiso is generally 20 PSI. So with a thin plywood the only thing I'd be worried about are point loads like stiletto heels and similar high loads on a small area. For normal, whatever that is, day to day use foam with 1/4 should be okay, with 3/8 better.... That assumes something solid under the foam, like 3/4 plywood with 24" framing; maybe 5 layer 1.2: plywood would be satisfactory . With thin plywood under the foam I can not guess what the minimum spacing should be to prevent sag and possible break through.

[KCStudly]

My 5mm (3/16 inch) ply over 1-1/2 foam has a little give to it. The frame in my sandwich is a combination of 2x2 and 1x2 on edge about 16-1/2 inches c/c. I think for a standy I would go with 3/8 nominal ply for the top skin.

Now don't forget, if you are being weight conscious, you don't need to use thicker ply under cabinets and other areas where you will not be walking.

[kudzu]

This is something I've pondered. My plan was to use a 3/4 foam sandwich. Though I had considered 1/4 for the top layer, I just don't think it would be strong enough long term for my use. Actually I've wondered if even 3/8 would be thick enough but I believe it will be. ...especially since I don't own stilettos... For the bottom I thought 1/8 plus canvas & paint would be enough. The intention is to have not only a framework of 1x2's but also a couple of 1x2's spaced out lengthwise through the floor.

For me, the purpose is to have an insulated floor. While weight savings would be a nice benefit, I'll settle for it not being any heavier than just using a thick piece of plywood.

Edit: It's actually 7/32 thickness for the bottom now 1/4. (I'm a little confounded by the variety of thicknesses of plywood products.)

[KCStudly]

Yeah, I bought some cheap 1x3 for my work bench the other day and it wasn't even 3/4 thk; more like 11/16.

I just wanted to clarify, on my floor, the whole thing is very stiff and doesn't seem like it weighs any more than an equal size of 3/4 (tho I did not weigh it by itself). It's just when I knelt on it it seemed to depress locally a tad (so I put a piece of 1/2 ply down to walk on during the build).

Doing a small test panel is probably a good idea if you really need to optimize for weight; make sure you will be happy with the 1/4 or 3/8.

[S. Heisley]

mdk, I am sending you a pm.