The issue I'm having is that ice builds up on the lower roof, creating a dam. The upper attic is double insulated, but is exposed to sun throughout the day. The lower roof (next to the sidewall) only sees sunlight for an hour or two very late in the day. So, the upper roof experiences some melt due to the sun and drops to the lower roof where it freezes creating a large dam against the sidewall. Eventually the ice backs up into the seams causing water entry into the interior.
Everything is insulated well, so I think I need to install de-icing cable along the upper edge, along the sidewall, and a bit at the bottom. See photo below - does this make sense, or is there a better way to lay it? Or are there other alternatives to avoid this issue?
My other consideration, is doing a piece of metal roofing (flashing) along the side wall, where the meltwater falls on the lower roof.