Versatile alternative to a flat roofed pergola
Retractable Bowed-roof Pergolas
A bowed roof retractable pergola actually qualifies as a Flat pergola, because the horisontal runners/guides are in a perfectly horizontal position. It is actually the canvass support tubes that are curved in the shape of a flat dome. These tubes are attached to, and support the canvass, bolted to the sliders in the runners.
When the roof is fully extended, the canvass is completely taut. This of course, is an advantage over most of the other flat structures which have slack, looped canvasses that can be blown around by the wind. The taut canvass accelerates the flow of water, which drains into an inner, surround gutter, which leads the water neatly into the pillars which also act as downpipes.
There is usually a certain amount of crumpling in the folds of the canvass, which does cause additional wear on the canvass over time, shortening the lifespan of the canvas by around 25%. The canvas can however be replaced when the time comes.