When replacing a roof it is important to pay attention to roof-to-wall flashing. In many cases previously installed flashing is too short under the existing siding. Many roofing contractors simply push new flashing under existing siding as much as they can. It is not a perfect scenario since siding boards are nailed on the bottom.
Being roofing and siding professionals at the same time we remove bottom boards of siding and inspect existing flashing while replacing the roof. If flashing is too short we replace previously installed flashing with recommended one by building codes. When new roof is installed, matching siding is applied on the walls, which is a proper way to integrate roofing and siding.