floor design questions

[Bezoar]

As I get ready to lay out my floor (building a 10 foot standee on an old pop-up frame) a couple of questions come to mind. I'm planning a plywood sandwich (1/8" road side and 1/4" on top) with "1 by" pine and 3/4" foam in the middle. I read that for us bigger guys, it will need internal support every 16 inches or so to feel solid. Unfortunately my recycled trailer's layout doesn't accommodate this. I want to make sure I put enough, but save weight and building time (and have foam for insulation) so don't want to add unnecessary internal wood pieces.

How do you decide where to put the wooden cross members? Many put them over the frame's metal cross members, but in Tony's book, he seems to lay them out more by what is built above them. I realize his floor supported a mattress, where mine will be walked on, so maybe that is the difference.

If not over a metal frame crossmember, wouldn't the wood deflect less if it were put on edge instead of laid flat?

How would two or three strips of 3/4 plywood glued together on edge compare in strength/support to a board of equal dimensions?

Any advice from folks who have used their trailer for a while and would do their floor differently? Or folks who nailed it the first time?

[tony.latham]

...wouldn't the wood deflect less if it were put on edge instead of laid flat?

That's why I doubled 3/4" plywood and installed them grain up for the cross members that didn't need to have anything screwed into them from above.

I was surprised not to feel any noticeable deflection when I was standing on it.

You may want to bump the underside sheathing up to 1/4" since I think that will add stiffness throughout the structure.

but in Tony's book, he seems to lay them out more by what is built above them.

And that's exactly what I did so the plywood edges had support. (Plus a "joist" in-between.)



You could run the "joists" every 12" of course.

Tony

[NevadaBlue]

I would put a cross piece at least every 16”. I’m not sure why you don’t want to do that.



1/4” ply isn’t very stiff and even though the foam is there, IMO, the wood reinforcement will be worth doing.

[linuxmanxxx]

If you use a good lattice pattern and completely glue the wood to wood portions with wood glue and then some foam safe glue on all the foam to wood surfaces and you will be able to walk on a 3/4" floor no problems. The glue surfaces are much stronger than going thicker and inverted. You will have to invert the roof for sure since it doesn't have anything supporting it like a trailer frame.
Steve

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[NevadaBlue]

Like you (and Tony) said, plywood on edge. But, do a test. Cut a piece and note how easy it is to break. 3/4” wide isn’t very wide or strong. Tony’s build was for a bed, not a ‘floor’.

IMO, use a “1x2” (3/4” x 1.5”) every 16”, just like a house floor.

How about a pic of your trailer frame. It would make suggestions a lot more informed.

[saltydawg]

My vote is frp bottom skin, 3/4 or 1 inch 25 psi dow foam, 1/2 baltic birch ply. All glued together with epoxy.

My floor is frp on boath sides and my supports are 24 on center.

[Bezoar]

When I try to shrink the schematic I drew enough to upload it, it becomes unreadable. here is a pic of the frame with my helpers before we started "de-rusting" it.

The main "box" is 76 in wide and 118 in long.

[eLink]

If this is going to be walked on, and it's more than 6' wide, I would suggest upright 1x2s spaced at 12" minimum. Doubled-up under bulkheads. Also recommend 1/2" minimum plywood on top.

[linuxmanxxx]

When I try to shrink the schematic I drew enough to upload it, it becomes unreadable. here is a pic of the frame with my helpers before we started "de-rusting" it.

The main "box" is 76 in wide and 118 in long.

Your going to need to raise the floor to clear the tires. Maybe use 2x4 frame you can match to the lattice in your floor. That would raise it 3 3/4" and give a perfect platform to attach to.

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[noseoil]

we used 3/4" poplar for the framework, 1/8" Baltic birch skins, foam insulation, added an extra 1/8" to the galley & 1/4" Baltic birch where the butt sits on the floor at the door openings. No problems with this build so far...

[tony.latham]

...we used 3/4" poplar for the framework, 1/8" Baltic birch skins, foam insulation, added an extra 1/8" to the galley & 1/4" Baltic birch where the butt sits on the floor at the door openings.

Said the guy that designed roof trusses for a living. (Howdy, Tim!)

Tony

[Tom&Shelly]

...we used 3/4" poplar for the framework, 1/8" Baltic birch skins, foam insulation, added an extra 1/8" to the galley & 1/4" Baltic birch where the butt sits on the floor at the door openings.

Said the guy that designed roof trusses for a living. (Howdy, Tim!)

Tony

May as well steal (ideas) from the best!

Tom