Why 2X framing under floor?

[TimC]

I am planning my build and hope to over lap the walls over the 2x2 steel tubing trailer frame. I'm thinking 3/4" BC plywood floor and walls. Just wondering why folks here use a 2x frame under the ply floor. Is it primarily for positive attachment to the walls? I see a couple posts about doing it to raise the floor height, which I don't need/want to do. I don't want to drill into my 2x2 tubing so will likely weld tabs on the frame and attach the floor with them. Thanks for any advice. I'm quite apprehensive about the finishing techniques (hatch, doors, windows and weatherstripping) and I'm glad I found this forum to help out.

[KennethW]

I did no use the 2x2's I screwed and glued a spline to the floor(for under the floor) before mounting the floor down. Then I set the wall over the spline.

[noseoil]

The job of the framing is to support the skin attached to it, too many people forget this simple rule of building (house, plane, boat, trailer). At work we do roof systems, we're a residential roof truss plant here in Tucson. I work as an estimator and deal with lots of different load case scenarios. A "standard" roof deck is made to withstand loads which are dead loads (static or just sitting there type loads, like roofing, pipes, insulation, plywood, etc) and live loads (loads like the wind in a thunderstorm, a large plumber walking around with his tools, etc). This is normally 2' on center for the trusses and 1/2" plywood (or more commonly now, OSB) for the deck. Expand the spacing & you need thicker plywood. Reduce the spacing of framing members and you need less thick material.

My trailer deck is 1/8" baltic birch top & bottom, with 3/4" poplar & 3/4" foam as the framework. I won't walk on this 1/8" skin, as it would likely hole & I would go right through to the ground. With the mattress in place, there won't be a problem since the mattress will help spread the loads across the panels & framework, & act as part of the support system for loads. I'll use 1/2" OSB for decking during the build, then remove the pieces after it's finished & ready to roll.

Sorry about the diatribe, but 2x4 framing just isn't necessary if spacing is smaller for a trailer floor. You can use 1X2 frame members 1' on center & 1/4" plywood for the deck IF you don't walk on it during the build. The bottom skin can be 1/8" if it is well sealed from the elements and glued in place properly. Tabs welded to your frame will be fine.

[halfdome, Danny]

I am planning my build and hope to over lap the walls over the 2x2 steel tubing trailer frame. I'm thinking 3/4" BC plywood floor and walls. Just wondering why folks here use a 2x frame under the ply floor. Is it primarily for positive attachment to the walls? I see a couple posts about doing it to raise the floor height, which I don't need/want to do. I don't want to drill into my 2x2 tubing so will likely weld tabs on the frame and attach the floor with them. Thanks for any advice. I'm quite apprehensive about the finishing techniques (hatch, doors, windows and weatherstripping) and I'm glad I found this forum to help out.

I put a plow on the walls to receive the floor and I see no need for a wood frame, if you use the welded on tabs like you mention.
Just make sure you use a weatherproof glue and plenty of fasteners where to walls attach to the floor.
My floor is bolted ( 3/8" elevator bolts and lock washers ) to 1/8" x 1 1/2" x 5" long angle tabs on my 1 1/2" x 2 1/2" welded chassis in about 20 spots.
To bolt a lumber frame to a chassis and then attach a plywood floor to the wood frame is in my opinion a wasted effort with no real gain.
Bolting to the welded on tabs is quite strong for a torsion box constructed teardrop trailer.
Danny

[noseoil]

What Danny said about the dado is how I'm doing my wall-to-floor attachment. The floor panel has a groove about 1/8" deep X 1" wide for the wall panel to sit in on both sides, and fasten up from the bottom of the floor. The wall panel is 3/4" plywood, which has been "skeletonized" to remove weight, and has a layer of 1/8" birch both inside & outside. This is about an inch wide and sits in the groove. The deck screws fasten up through the bottom, through the 3/4" poplar frame edge, and up into the side panel frame. The screws hold it in place and act like clamps, while the glue does the actual fastening.

Here's the side panel sitting on the frame. It shows how the side will sit on the deck, which then sits on the frame. I'm using 5/16" bolts to fasten to the frame. A grade-2 5/16" bolt (hardware store type) has a single shear rating of about 3400#. I'm using more than one (actually 9 bolts), so I figure it will take about 30,000# of force to shear these bolts loose from the frame. If that happens, I have other bigger things to worry about than a few broken bolts.



Here's an image from today. I ran the aluminum edge for the galley, but it shows the rabbet for the side & one screw hole where the side fits into the deck.

[ctstaas]

Hi Tim, Here's my $0.02 worth. My TD is a 4 x 8 Benroy type. My pull tube/ tongue is strong. 3" x 3/16" square A36 tubing. The axle tube is the same size and is welded to the tongue tube. My torsion axle brackets are welded to this tube. On the back of the axle tube another 3 x tube forms a cross and holds a receiver. The exterior of the frame is 1 1/2" x 0.065 square tubing. I built my cabin separately and rolled the cabin onto the frame with a piece of pipe. I bolted the cabin to the frame. The frame gives strength to the cabin and vice- versa. Light weight and strength are achieved with good design.
Enjoy, Chris