Why the two scopes meet
PNNL's existing-home guide treats flashing at a roof-wall intersection as a detail connecting roof and wall water-control layers. It addresses roof replacement as well as exterior-wall upgrades and calls for existing-condition assessment and project-specific detailing. This educational guidance does not determine a property's design, current code, contractor responsibility or universal work sequence. U.S. Department of Energy Building America Solution Center / Pacific Northwest National Laboratory, “Flashing of Roof-Wall Intersections in Existing Homes”.
This is a scope comparison, not an installation guide or leak diagnosis. The guide does not tell you which contractor should do the work or which order is right for your home.
Link each proposal version to the same locations
Start with the two actual proposals and their dates or version labels. Mark only the wall-roof locations that both scopes may affect. For each location, compare what the roofing proposal says will be opened, retained, restored, or excluded with what the siding proposal says about the same area. If one proposal describes a boundary and the other does not, they are not yet describing the same job.
Keep a copy of the two versions together. Ask each project lead to reference the other proposal, identify who coordinates the shared junction, and state the sequence they propose and its dependencies on the other scope. Record that project-specific sequence in both linked proposal versions; this is a request to compare proposals, not a prescribed trade order. A combined contract does not by itself show that every transition is included; separate contracts do not by themselves show that the work is incompatible. The written boundaries and named responsibility matter more than the number of contracts.
If the condition will be known only after work begins
Do not treat an unobserved area as verified. Before authorizing work at that interface, ask the contractors to identify what can be reviewed, how they will document a newly exposed condition, who will contact you, and how a changed scope is described and approved before additional work proceeds. Ask what access and review point they propose before the junction is covered again. Leave the condition, repair extent, cost, and technical solution unresolved until the responsible professional assesses them.
Compare like with like
Use one row per affected location: both proposal versions; included and excluded work on each side; retained or newly exposed components; the sequence and dependencies each lead proposes; who coordinates the junction; the proposed review and documentation point; and the written change process. Ask which completion records each contractor will provide for that shared junction and how the handoff between scopes will be recorded. If a detail or access plan is missing, ask both project leads to clarify the boundary and handoff. Do not assume a combined contract or a particular trade order is better. Compare totals only after the shared boundary and exclusions are clear. The comparison's purpose is to show where the two written proposals align and where an owner must request clarification.