The easiest way to shorten fabric louvre vanes is to unclip each vane to take them down, lay each one out flat and measure from the bottom up. Turn over the excess and machine stitch a new pocket large enough to slide the clip back in. I usually use a heavy weight when I fold them down to make a good crease. Cut off the excess fabric before stitching. Some of the companies use a glue but you must be careful to get one that will not turn the fabric yellow. Good luck.
Retired fitter., November 2008
