Contractual obligation

I'm a contractor in California. i have a customer who i did a complete roof for. He had another contract install an awning and the tucked their roof under mine. The shingle were never put back properly and have created a leak. Does this legally void my warranty?

If that is truly the case, then your not responsible to repair it under warranty. However, the rest of the roof should remain under warranty.

PS: I would see it as an opportunity to make some money repairing the other contractor's mess and retain a happy referring client at the same time. Killing two birds with one stone! ;)