roof drain downspout ice melt question
I have a flat roof and two roof drains that exit the back lot of the building about 10 feet in the air with 2.5"(i think) PVC pipe. I have 8 Watt/foot heat cable inside of each drain in a loop (so "double" the cable inside the pipe). the pipes open end is about 3 feet off of the ground. the water drips out and freezes on the driveway, forming an enormous icicle which grows all the way up to the pipe and freezes the inside of the pipe as well. the heat cable simply cannot keep up with the ice, and the junction of where the pvc meets the metal drain inside the ceiling will end up blocked, and water will overflow out the plastic trap door (plumbing access) in the ceiling. how to avoid this?
1) Code doesn't allow for the water to stay inside the house and drain into the sewer system
2) I don't know if 1" foam pipe insulation will help much, since the pipe is open on the bottom anyway. Maybe a $300 gamble
3) A heat mat on the driveway will be $100, plus just be more electricity
4) More powerful heat cables such as easyheat SR81 would be at least another $1,000 including labor, and don't know if it would make a difference
5) Sealing the junction of the PVC and metal drain pipe inside the ceiling would cause the water to sit on the roof, and then if that froze, it would rupture the seam between the drain and the rubber roof and be catastrophic. at least water coming out of the ceiling into a bucket is a relief valve of sorts
6) Knocking the icicle away and banging on the pipe with a hammer is the low-tech solution, but the icicles don't take long to grow back