Step Flashing

Step flashing consists of L-shaped metal pieces installed in a stair-step pattern where a sloped roof meets a vertical wall, such as at dormers, sidewalls, or chimneys. Each piece is woven with the shingles—sitting on one course and under the next—creating overlapping layers that shed water away from the wall. Step flashing is critically important because wall-roof intersections are highly vulnerable to water intrusion. Without properly installed step flashing, water running down the roof would penetrate behind the wall covering, causing hidden damage to wall framing, insulation, and interior finishes.

Signs of step flashing failure include: interior water stains on walls below roof-wall intersections (often appearing far from the actual leak), peeling paint or wallpaper on interior walls, visible rust or corrosion on the flashing metal, gaps between flashing pieces, flashing pieces that have lifted away from the roof surface, deteriorating caulk at flashing edges (which often indicates underlying problems), and mold or musty odors in wall cavities. Sometimes step flashing failure isn't visible until siding is removed, which is why professional inspection is important when water damage is suspected at wall-roof junctions.

Step flashing and counter flashing work together as a two-part system. Step flashing consists of the individual L-shaped pieces woven with the shingles, with one leg under the shingles and one leg extending up the wall. Counter flashing is installed over the top of step flashing to cover and protect its exposed upper edge—at masonry walls, counter flashing is embedded into mortar joints; at other walls, it may be surface-mounted or integrated with siding. Both components are necessary: step flashing provides the primary water barrier, while counter flashing protects the step flashing from direct water entry and helps shed water over it.

Step flashing repair depends on the extent of damage. Individual lifted or damaged pieces can sometimes be repaired by carefully lifting shingles, replacing the affected piece, and re-securing the shingles. However, because step flashing is woven with the shingles, extensive repair often requires removing multiple shingle courses. If rust or corrosion affects multiple pieces, or if improper installation is discovered, complete replacement of the flashing section is usually more cost-effective than piecemeal repairs. The best time for comprehensive step flashing replacement is during a reroof when all shingles are being replaced anyway.

Aluminum is the most common choice for step flashing because it's affordable, lightweight, easy to work with, corrosion-resistant, and available in various colors. Galvanized steel is stronger but may rust after the zinc coating deteriorates, particularly in humid coastal climates. Copper is the premium option—extremely durable and develops an attractive patina, but costs significantly more and requires matching any counter flashing to avoid galvanic corrosion. The most important factor is matching the step flashing material to the counter flashing material; mixing dissimilar metals (like aluminum step flashing with copper counter flashing) causes galvanic corrosion that destroys the less noble metal.

Kick-out flashing (also called diverter flashing) is a special piece installed at the bottom of a wall-roof intersection where the step flashing terminates near a gutter. Its angled shape 'kicks' water running down the step flashing system into the gutter rather than allowing it to continue down behind the wall covering. Without kick-out flashing, water concentrates at this transition point and enters the wall cavity, causing severe hidden damage. Kick-out flashing should be installed wherever a roof slope intersects a wall that continues down past the eave line. Missing kick-out flashing is one of the most common and damaging flashing deficiencies found in inspections.