1) Design evolution. As we built the greenhouse we suspected the rain pooling to be a problem so we shortened the distance between the apex (peak) of the roof and it's short side. This would limit the surface area potentially at risk.
2) Support. We used twine to attach from the fence to the ridge pole. This would then provide a measure of support to the plastic and would limit the areas of pooling by maintaining high spots every few feet. In addition, we extended the twine to the ground on the opposite side to provide an added measure of stability to the structure.
3) Tension. We concluded that if we keep the plastic tight enough that the rain would simply drain and no puddling would ever occur.
4) Tension support. We suspected there may have been some inaccuracy in our measurements, plastic measurements, fitting of our frame, etc., which caused slight dips in our otherwise perfect design. We were able to correct a measure of the error by pulling some of the excess plastic and taping it with duct tape. This helped, in a measure, to restore the tension. (This was done after it was already raining and puddling has started to occur. Michelle had me hold the umbrella over the work area while she dried the plastic with a rag enough to attach the duct tape.)
5. Mid-structure support. When the tape failed to eliminate the pooling Michelle added additional supports in the middle of the plastic, at regular intervals, to create a steeper run-off which would help eliminate low spots and would allow the rain to drain. She used some left-over gardening sticks (from a previous garden) to push the plastic up. The concern with these poles was that they are thinner and since they are essentially just sticks we were concerned that if enough water managed to pool, these poles may just poke through the plastic.
6. More Mid-structure support. If one pole doesn't work try more. The pooling continued so Michelle added additional poles. It seemed to work but we now realize that it was a slow down in the rain that gave us that false sense of accomplishment.
Now it is 6:00 am and raining again and it is raining pretty constantly. I woke up to the sound of the rain and then I realized another solution to the dilemma of the pooling water. Add drains. We've been able to determine where the water is most likely to pool. Since those spots are the obvious low spots, we can just add drain spouts in those spots which would allow the water to drain instead of just collecting and pooling. The idea is simple, the design a little more complicated but my current thought is that we can poke a hole at the bottom of the pooled water area (after draining the water), insert a straw, extend the straw through the plastic side wall, and "seal" the 2 holes with duct tape. The straw will allow the water to drain below the side support and would be positioned to drain the greatest amount of water without creating a place for the heat to escape the greenhouse. I'll have to try it when it gets light outside.
