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  • Writer's pictureJim Martin


With the plywood laid down, it was time to get to the floor joists. But the basic box of the trailer is 20 feet long (adding the hitch it’s a total of 24 feet). The challenge here is I can’t find 20 foot 2x6s to lay in as joists. There are lots of options for how to span the 20 feet, of course. You can overlap pairs of joists, for instance. But I really wanted a clean run from end to end. Among other things, it would make laying in the insulation very simple and tidy.

So, I opted to cut scarf joints into paired 2x6s that would total 20 feet, making sure the scarf joint landed right over one of the metal frame members of the trailer. A scarf joint is a clever method for joining two pieces of lumber end-to-end using wedges to tighten the joint. It’s not intended to be used as a load-bearing joint, but for applications where the joint is supported, it’s a great solution. (Here’s a great demonstration of how to cut a scarf joint.)

I made a pattern to trace the joint out on the end of each 2x6.

Then I cut them out.

Prevailing wisdom is that the pattern can be used to cut out the first half of the joint, then that cut half is traced onto the second joist it will be joined to. (That'll make more sense if you watch the video linked above.)

Fitting them together was the most fun part. Our son Aidan was a champ. He loved the technical joinery!

Each joint is finished off with a nice long deck screw driven down roughly in the same place as the clamp in the above video. Here’s the first couple of joints all assembled.

We alternated the joints left and right (always making sure they landed over one of the framing members in the trailer frame).

And here’s the finished product!

Next we need to bolt the joists down to the trailer frame. Then the fun really begins!

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