The fabric held in place with staples. The initial plan was to cover the staples with a piece of 1x4 redwood, to match the thickness of the beams. That would have looked great, but in the end this detail was cut. The staples aren't visible since they are above so the trim was omitted in favor of cost savings. However, the trim might come in useful if you are imagining an application where the staples would show. Thanks for the interest!

what is the fabric used? How did you order/purchase? this looks incredible!

I love the look! How do you think would this fabric roof hold up in windy areas?

Thanks! Great question! Wind can pass through it, but it will slow the wind. If you are worried, I'd recommend adding a trim strip over the stapes so that the compression of the trim will ease some of the tension on the staples, making the less likely to pull through.