Keep Water Away With A Single Top Bar
Having just one central bar atop this polytunnel protects it from collapse due to water build-up. In other polytunnels, having two bars running the length means that rainwater can pool between them, putting a lot of weight on the structure and leading to potential collapse.
Polytunnels with vertical walls are much more prone to wind damage. With sloped sides, the shape of this polytunnel is designed to deflect the wind upwards, diverting some of the strength of the wind away from the side.