Framing the floor

Started the day by leveling the trailer with a laser level and the leveling jacks to get the weight mostly off the wheels. We’re using the leveling jacks while we frame the walls because they make leveling fast and easy, however, these are not designed for heavy loads so we’ll be switching to blocking right after the walls go up.

On the advice of Derin Williams of Shelterwise, we wrapped the pan with 1” XPS foam to create a full thermal break between the trailer and floor assembly. Note: Foam is easiest to cut on a table saw.

Next we set the rim joists in the pan and marked them out so the subfloor seams will break on top of the joists, and also noting the location of the holes in trailer frame. Note the joist hanger setting jig, it makes a surprisingly tricky task much easier. Structural screws are also nice if you don’t have a hard surface to hammer on.

Nailed the end joists on with common nails to avoid a hanger conflict with the predrilled bolt holes in the trailer, then dropped the whole assembly in and filled in with very tight fitting joists. The 2×6 floor frame sits 15/16 ABOVE the trailer flange to accommodate for 1” foam that will bridge across to the inside edge of the sill plate to complete the thermal break.

The floor frame wasn’t the right height everywhere so we carefully shimmed it up before drilling through the predrilled holes in the trailer frame and setting the 5/8 x 5 1/2” bolts that the assembly basically hangs on (think deck ledger) There’s a theoretical concern with shear forces here due to the foam break between the steel and the rim joist but the 5/8 bolts are so over spec’d that it isn’t a real life issue.

The cross beams on the trailer are strong enough to support the rim joists but I’m not so sure about the crushability of the foam so we opted to go the suspended route.

Our bolts are basic zinc coated, galvanized is unnecessary and gets expensive in a hurry.

– Brian

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