wibbus Thank you - I was looking for something like "multiplying it by 1.5" or "doubling the overall length," but couldn't find a calculation for this sort of thing. I hadn't thought about the height of the ceiling and how far the fabric would come down, so trying it out with string or ribbon is a good idea. I want to make it easy to remove for the winter - and for cleaning. We live in Colorado where there is a lot of dust!

Cynthia Taylor-Luce You're very welcome. This is a very interesting and practical treatment and not difficult to execute if you take your time and measure twice and cut once! :)

In fact, why not buy some ultra cheap fabric, just three or four yards and do a mock-up before you do the whole thing? I think you could sew this very simply by folding the fabric, stitching in a line (in from the fold) half the width of the casing you need. If you do this, there's no cutting, no extra fabric tube you need to create and sew onto the fabric. You'll definitely have to allow for the fabric that this uses up, when you make your calculations.

bepsf It's a custom fabricated item