As a new owner of a polytunnel I found this question quite a challenge. Apparently, on a straight-sided tunnel, you need the guttering to slope so that the rain water pours off the roof quickly to avoid too much weight of water putting a strain on the building. Unlike greenhouses, where the gutter is separate from the walls, the gutter of a polytunnel is part of the structure that secures the roof plastic. Therefore the entire roof line needs to be on a slope. We are planning to put in flood benches as a later stage therefore its quite important to us that the floor inside the tunnel is level. Yet, when we came to build the tunnel and needed to accomodate a 20cm drop over the 40meters. Therefore we have had to accept that the roof is lower at one end than the other. The result of this is that or walk-through side curtains are not parallel with the ground and when you drop them down one end reaches the bottom before the other. This is not a major problem but also seems like a slight design flaw. I guess most people either let the floor slope slightly too or only have flood benches in greenhouses. Comments please?
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