We built a sunroom on the front of the house. Luckily, that faces south. It is 9' tall and has 24' wide and has 8mm double wall lexan for glass. On sunny days when it is warm, we'll open the door and a window and let the heat in, maybe use a fan to blow it in. The ceiling is insulated. We're wondering what to put on the floor. We'll shut the door and window in late afternoon, but DW plans to start plants out there next spring. I thought some kind of dark rocks might absorb heat and give it off at night to keep things a little warmer. But would we need insulation under the rocks to keep the ground from sucking all the heat? What kind and how much? And how much rock? In the summer, the panels of lexan come off and it becomes a porch.