Why is this done?

[shortleggedsarah]

Hey teardropers,
I am a newbie looking to build my first teardrop. I am in the R&D phase of my project, doing some sketches and building a model on CAD.
My question is this: I have been looking at other builds, and it looks to me that most people build a frame of 2"x2"s on top of the chassis, to support the decking. Why is this done? Why not simply put the plywood decking on the chassis? Is it an issue of height, structure, or insulation?

Thank you for your consideration!

[mezmo]

Hi shortleggedsarah,

Welcome to the forum! Why not take a little time and introduce yourself in
the Newbies section?

A lot of construction details are really personal preference, or used because
of the intended usage or climate conditions. Directly installing the 3/4in
plywood onto the frame as a floor/base is a very simple and direct method used
by many, but isn't necessarily the lightest method. The sandwich framed floor/
base is done for different reasons. Depending on its thickness, it can become a
torsion box base or just a method to insulate the floor. [The topic of insulation
is another area of divergent opinions.] The floor sandwich is also used as a way to
facilitate attachment of the walls to the floor. I happen to think that an
insulated floor sandwich is a good idea, if only for the reason that it helps cut
down on interior condensation - which can be a problem in uninsulated units
outside of very dry climates.

Just keep looking around on the forum and checking out all the various build
methods and any explanations/reasons why they are done that way. Then, pick
out or combine any methods that you like and that make sense to you. And
always ask any questions you need to ask.

Happy planning!

Cheers,
Norm/mezmo

[S. Heisley]

Actually, 2x2 boards are not what I've seen recommended. 1x2 boards are usually better because you can cut some weight and you really don't need much more than that. It is my understanding that the deck framing beneath the plywood floor adds “bite” for the screws when attaching the sides, etc. If your floor is bigger than a 4x8’ plywood sheet, it is advisable to piece your plywood over top of one of these deck framing boards, to add extra support and to help keep a better glue seal at that point.

While the above is my understanding, others may point out other facts or beliefs as well.

Good luck on your build!

[Oldragbaggers]

My guess is that insulation in the floor is the main reason, at least that was the main part of my reason.

But some also do it because they build out over their frames and need a structure to support the portion of floor not on the trailer frame or, as Sharon pointed out, if your teardrop is any size other than the standard 4x8 you will have joints in your plywood floor and the planking gives a place to land those joints (the other part of my reason).

But some people do exactly as you said, and if that suits your purpose well, then by all means benefit yourself from the simplicity and reduced cost of doing it that way. We'll be interested to see what you decide to do after you have concluded the "R" part of your R&D period.

And Welcome to the Forum!!

[Woodbutcher]

My current build is done with a 1/2" floor resting on the frame cross members and the walls built above the floor, this gave me floor strength and maximum inside height. I don't camp in freezing temps so I don't find insulating the floor is needed. Plus a 6 Inch foam mattress will insulate enough. Not the best picture but you can get the idea.

[Oldragbaggers]

Woodbutcher, you really need to change your sign in name to "Woodmaster" or something similar. Woodbutcher just isn't right on so many levels. You are a master craftsman!

[Ron Dickey]

I used Kill dried 2x4's reduce weight and will not worp.

[mikeschn]

I think Sharon is the closest.

I use 2x2s for the subfloor so that I have something to drive the screws into. I also clean up the edges with a circular saw, so they are flat and perpendicular, so that when I attach the walls, they are well supported AND also vertical!

If I were to attach the plywood directly to the steel chassis, then I would probably want to add a structural support above the plywood floor to attach to the walls!

Mike...

[bobhenry]

I got it backwards my osb floor supports the 2x4 halo that the walls were later attached to.

[Nobody]

Since I was using the 1740# 4X8' HF trailer w/12" wheels/tires, & wanted a 5' wide TD, it meant the cabin would extend over the tires on each side. It was therefore necessary to devise a way to incorporate 'wheelwells' without intruding too high into the cabin space. After careful measurement I decided that 2x6's (approx 2 5/8") ripped in half would provide the needed space for wheel/tire clearance & only intrude an inch or so into the cabin. I also wanted to 'hide' the trailer chassis so I used 1x6 boards as side rails for the floor assembly, with the excess width 'hanging' below the floor. Couldn't find/afford a piece of 5x10' half inch plywood for the floor so I 'pieced' it together from 2 sheets of A/C exterior grade ply. After completing the floor I turned it upside down, coated with asphalt roofing 'goo' & then insulated with 1" foam 'Dow Blueboard' placed in the framing recesses. Used construction adhesive on the foam & then stapled 'battens' from scrap to hold the foam in place before fastening to the trailer chassis with eight 3/8" carriage bolts. For 6yrs & more'n 12K miles the insulation has stayed in place & there is minimal damage/marks from road debris to the exposed foam.

The extra 'thickness' of the floor assembly also provided 'holding' material for fastening the walls in place. My walls are sandwich construction, built from inside out, flat on a table. After staining/varnishing the 1/4" oak plywood interior skin & adding 1x2' framework, walls were erected onto the floor, held in place with braces/clamps, & then fastened directly to the floor using construction grade deck screws & PL5200 adhesive. Walls were then insulated, skinned with 5mm luan, roof spars/insulation/luan added, followed by aluminum skin & diamond tread trim.

I'm sure there are other ways, probably stronger, lighter, & maybe easier to build but this was my way & during Labor Day weekend 2010, the TD cabin withstood with minimal damage a rear end collision that caused considerable bending/twisting of the rear cross member & left side reail of the HF trailer chassis.

Oh yeah, after all my careful measurement/calculations, after a few thousand miles over some pretty rough roads I found that the tires would occasionally contact the bottom of the wheel wells so I added a 1" steel spacer between the axle spring seat & the springs, eliminating that minor problem...

[shortleggedsarah]

Thank you all for your great replies! Goodness you are a helpful bunch!

[DMcCam]

Hi shortleggedsarah,
I actually did use just the plywood glued and bolted directly to the frame. I used 1" decking tongue and grooved into a single deck.



My walls have a 3/8" mortise on the bottom to hang on the deck. They were glued and screwed (after pre-drilling) to the ply.

Cheers,

Dave

[shil]

For my first trailer I used T & G plywood screwed right to the frame. I see no reason not to do that again.

[rowerwet]

if you check my WWW you'll see I went way overboard on underfloor framing, I ripped all of that off recently, by current floor on the TD is just 3/8 marine plywood, due to my using a welded trailer made of angle iron I have had to make some "frame" but it is only 2x3's on the outer edges to fill the trailer and make it flush. on top of that I have one sheet of 3/8 marine ply, this will be glued to the current floor of the TD using construction adhesive (PLpremium).
My TD is a 5' wide one, I figured out that the front wall and the wall at the foot of the bed are all that are needed to support the roof and sidewalls weight as both of those walls bridge the 6" overhang of "unsupported" plywood from the trailer frame to the wall. My walls are double skinned with 1x2 inner framing, the floor is glued and screwed (the only joint with screws remaining) to the wall framing. The TD floor is made of two cross wise sheets of ply, the length wise sheet is mostly to close the "gap" between the two sheets which falls at about the front of the wheel wells.
personally I think most TD's floors are overbuilt, reinforced like they will be used as a cargo hauler, rather than just a bed. (says the guy who just removed about 100 lbs of 2x4's from his floor)