I would think the water is running down the outer walls of the solarium and then under the wall. Water could be running across the deck to the wall. If you're reframing, put a seal under the frame against the deck. I think the material they use on new houses between the frame and foundation is what you want. It's a thin layer of the foam about 4 to 6 inches wide. Otherwise you need to caulk around the exterior edge of the frame. Depending on the location of decking gaps, you could use flashing that is fitted into the gap to put the water under the decking.