Framing and Insulating the Floor

Once the trailer was leveled, front to back and side to side, it was time to begin construction. 

The first step was to put metal over the trailer frame. This trailer, by Tiny Home Builders, has angle iron running along the length of both sides, and runners going the length of the trailer on which to attach the metal and the floor framing. Other trailers, utilize cross members, and it's possible to use rolls of flashing to lay strips from front to back to cover the trailer. The recommendation for this trailer is to use sheets of roofing metal. I used 29 gauge pro-panel, which probably isn't ideal. It looks nice, especially underneath with the black side down. But, a lower profile metal sheet would flatten more easily across the front and back frame members.

I did the floor framing in three sections. The middle, between the fenders, was separate from the ends. I used 2x6s which provided two inches more space for insulation than 2x4s. Nice for cold weather, but it does reduce the potential height of the tiny house by the same two inches. The trailer has a drop axle to make up for the deep floors.

You can't really tell from the photo, but the eighteen inch section at the back end is cantilevered out past the end of the trailer. It was done that way to support a full width utility cabinet and add some length to the loft above.The joists in this back section run lengthwise to provide support for the cantilever.

Similarly, in front is a cantilevered bay window area over the tongue. The triangular shape of the bay uses the space well, but still allows for sharp turns. 

The frame was bolted down with 3/8" galvanized bolts running through 7/16" holes drilled into the 2x6 frame and the angle iron. The bolt head and washer were recessed below the surface, and filled with epoxy. Once the floor sheathing is put over the top, the epoxy around the bolt head will help keep it from turning if it should ever require tightening. But the bolts are long enough that you can get a vice grip on the end of the bolt while tightening the nut, and the nut is secured with Loc-tite thread sealant as well. 

To fill the cavity left by the 2x6 framing, 5-1/2 inches of insulation was required. I used R-Tech rigid insulation from Home Depot. It took two thicknesses of 2-inch insulation and two thicknesses of 3/4-inch insulation. That filled the 5-1/2 inches and gives the floor about R-21.