Roof-to-wall transitions — step flashing required course-by-course, continuous flashing limited situations, counter-flashing on masonry

Roof-to-wall transitions are the install detail where a sloped roof plane meets a vertical wall — a side wall of the main house, a dormer, a chimney, or any other above-roof vertical surface. These transitions are the second-most-common roof leak source after pipe boots (cross-reference KB-D4-014) and the install discipline matters because the transition handles water from both the roof slope above and any water running down the wall surface. Step flashing is the IRC-required method per R905.2.8.3 — individual L-shaped or step-shaped metal flashing pieces installed course-by-course, with each piece integrated between two adjacent shingle courses. The vertical leg of each step piece extends up the wall (typically 4-6 inches); the horizontal leg extends onto the roof (typically 4-6 inches) under the next-course shingle. The course-by-course installation creates a "stepped" pattern of metal pieces ascending the wall, with each piece providing a redundant water-management layer. Step flashing produces multiple overlapping water-management layers — water flowing down the wall reaches the step flashing's vertical leg, then is directed onto the step's horizontal leg, then onto the field shingle below, then off the roof. Continuous flashing — a single long piece of metal flashing running the full length of the roof-to-wall transition — is permitted in narrow situations (typically where the wall transition is parallel to the roof slope rather than perpendicular, such as at a porch overhang's outer edge), but it is generally inferior to step flashing for water management because it provides only one water-management layer, and any compromise of the single piece (a cracked solder joint, a dented section, an animal-chewed gap) creates an immediate leak path. Most current IRC cycles permit continuous flashing only with specific code-cycle conditions; check the cycle adopted by the local jurisdiction. Counter-flashing on masonry walls and chimneys is the second flashing layer required where the transition meets brick, stone, concrete, or stucco. The step flashing's vertical leg extends up the wall, and counter-flashing is cut INTO the masonry mortar joint above the step flashing, bent down to overlap the step flashing's upper edge. The counter-flashing's purpose is to prevent water flowing DOWN the masonry surface from running BEHIND the step flashing. Without counter-flashing, masonry-wall transitions leak water down the wall directly into the wall cavity and ceiling. Counter-flashing replacement is one of the most common chimney repair items on aging roofs because the masonry mortar joint degrades and the counter-flashing falls out of its slot. Kickout flashing is a specialized step-flashing variant required at the lower end of a roof-to-wall transition where the wall continues PAST the eave (typical at a house where a dormer or side-wing wall continues below the main roof's eave). The kickout's role is to direct water OFF the lower edge of the transition rather than letting it run down behind the wall siding. Missing kickout flashing is a common installer mistake that produces a specific wall-rot failure mode behind the siding at the lower corner of the transition. Common installer mistakes include: caulk-only at wall transitions (a near-immediate leak failure mode and an automatic warranty void); using continuous flashing in step-flashing-required situations; omitting counter-flashing on masonry walls; omitting kickout flashing at lower wall-transition corners. Texas / Houston relevance: roof-to-wall transitions handle higher water loads in the Houston Gulf Coast wind-driven rain pattern than in dry climates, and the masonry counter-flashing decay is accelerated by the high humidity. (Cross-reference D8-006 for wind-damage patterns at wall transitions.) [Source: International Residential Code R905.2.8.3 wall and base flashing requirements (2021 and 2024 cycles); NRCA Roofing Manual asphalt shingle wall flashing chapter; ASTM A653 standard for coated steel sheet (flashing material specifications); manufacturer install guides specifying step-flashing requirements for system warranty]