An addition can change roof geometry and the amount or direction of runoff reaching existing drainage components. The original arrangement should not automatically be assumed adequate for the changed building. Coordination belongs in the project planning.
What to do next
Ask the responsible design and construction team to review the combined roof drainage. Identify new valleys, transitions, and outlets. Keep the resulting details with the project documents so future maintenance understands how the old and new areas are intended to work together.
Related Perkins guidance
Contact Perkins Roofing to discuss your roof and the appropriate next step.