Where roof sections meet over the house and garage
A house can have a lower roof over the garage meeting the wall of an upper story. At that junction, water needs a continuous route from the wall onto the roof and away from the house. Flashing and the material behind the wall finish work together to create it.
When that connection leaks, the visible stain may be over the garage even though water entered higher up. Replacing shingles beside the wall without reaching a failed upper flashing connection can leave the cause untouched. Inspection and repair need to account for how the roof and wall were assembled.
Where two slopes meet in a valley, water from both sections runs through the same channel. Damaged covering or a poorly integrated repair there can affect more than one slope. The inspection needs to follow that shared water path and check how the valley joins the surrounding roof.
The same layout affects replacement scope. Garages, porches and separate lower slopes can add roof area that is absent from the living-area figure. A measured roof scope includes those sections and the details where they meet, rather than assuming the house’s indoor square footage describes the job.