Join J-Channel With a Slip Joint, Not a Butt Joint

The Problem

Butting two lengths of J-channel end to end leaves a visible seam that opens into a gap as the vinyl moves — and vinyl always moves. The joint needs to overlap, look continuous, and still let the material slide.

The Technique

1. On the first piece, cut a 45 across the front corner of the channel's face.
2. On the mating piece, cut the back corner at an opposing angle, with a second cut meeting it — and make sure the lower of the two cuts runs past the upper one, never short of it. The overlap direction is what hides the seam.
3. Make one more short cut where the pieces will enter each other.
4. Roll the second piece into the first and tuck its nailing flange in behind.

Done right the two channels read as one continuous line, and the loose overlap is the expansion joint — the vinyl slides inside the joint instead of opening a gap at it.