Christopher, in situations like this a standard windward/leeward drift check often isn't enough.
When a new taller structure creates a narrow valley next to an existing roof, it typically acts as a snow-trap, so you should also consider a valley / unbalanced drift case in addition to the regular drifts.
In practice the safest approach is to treat the area between the two roofs as a separate drift load case with a larger effective drift height and width, since snow tends to accumulate more aggressively when it's confined on both sides.
It's a common issue with additions to existing buildings - we usually check windward, leeward and a "captured snow" case as separate load scenarios.
If you can share the height difference and the horizontal gap, I can sketch what that load case might look like.
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Darya Stanskova M.ASCE
Cost Estimator, Construction Engineer, Power Engineer, Project Manager
Fort Myers FL
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