This discussion is specifically designed for information related to Greenhouse design for those of us in zone 8. What coverings will work best based on our temperature price and expected length of service. What will grow best in a green house when in zone 8. What are the challenges we might face with water temp as we see temperatures in the teen's and 20 December threw February and 90-110+ June threw August. What types of systems might help with the extreme temp changes. Location and direction of green house typical you would want a S-SE sun exposure green house would that still be best?
I've given serious thought to a hard-structured greenhouse but have decided on a simple canvas "portable" greenhouse. The requirements (given our zone) would be adequate ventilation and fans (and/or other cooling methods) for the summer heat. I've found that heating is not as difficult in the winter if one uses a simple canvas or plastic covered greenhouse. I made a makeshift greenhouse over my grow beds last Winter and used two 500 watt heaters in a 200 gallon tank. The water from the tank kept the grow beds relatively warm and, with proper insulation, the fish stayed comfortable as well. I did set my tank temperature down to 20 degrees Celsius this last Winter.
Down here, I have more issues with Summer heat than Winter cold. Even with shade cloth over my grow beds, I have difficulty keeping lettuce, cilantro, and basil from bolting. Although, the one plant that seems to defy all attempts to kill it in the Summer is eggplant. Check the pictures I posted on the eggplant I grew last year. Two plants must have produced 30 to 50 eggplants just like the ones in the picture. After a month or so, I was giving them away.