Split trouser hems can add a touch of glamour, adding a trim takes it up a notch!
This variation is for a double jersey fabric construction like a Ponte Roma or similar -the edges of the vent are raw; these could be finished with an overlock stitch or turned although this will add bulk.
Decide on the length of your vent, the ones shown here are 22cm.
Add an extension to the pattern piece as illustrated (24cm x 4cm). On each cut trouser leg add the trim to the centre of each extension piece, stitching down either side of the trim. Then when stitching the outside seam, stitch from the waist to the top of the vent, then along the top of the vent. On the wrong side, fold the vent towards the back leg, press and stitch across the top of the vent to hold in place. Complete trousers as instructed.