Roof-to-Wall Flashing

What Is Roof-to-Wall Flashing

Roof-to-wall flashing is the waterproofing assembly installed wherever a roof plane meets a vertical wall surface. This is one of the most critical flashing details on any residential roof because it handles the transition between two different building planes that move independently and shed water differently. There are two primary configurations: sidewall junctions, where the roof slope runs parallel to the wall, and headwall junctions, where the roof slope runs into the base of the wall. Sidewalls are flashed with step flashing woven into the shingle courses. Headwalls are flashed with continuous apron flashing. Both methods require a minimum 4-inch leg on the wall side and a 4-inch leg on the roof side to provide adequate water protection.

Sidewall vs. Headwall Details

At a sidewall, each step flashing piece sits on top of the shingle below and is covered by the shingle above, creating overlapping water barriers at every course. The wall leg extends up behind the siding or exterior cladding. Proper installation leaves a gap between the bottom of the siding and the roof surface to allow drainage and prevent moisture from wicking into the siding through capillary action. At a headwall, a single continuous piece of bent metal runs the full width of the junction. The roof-side leg extends at least 4 inches under the shingles, and the wall-side leg extends at least 4 inches up behind the siding. A cant strip or cricket behind the apron flashing can be used to prevent debris and water from pooling at the junction on lower-slope headwalls.

The Kickout Flashing Requirement

At the bottom of every sidewall-to-roof intersection where a gutter is present, a kickout flashing (also called a diverter flashing) must be installed. This angled piece catches the water running down the step flashing assembly and directs it into the gutter. Without kickout flashing, water cascading off the bottom of the step flashing runs behind the siding, saturating the wall sheathing and causing rot, mold, and structural damage that can go undetected for years. Many building codes now mandate kickout flashing, and its absence is one of the most commonly cited defects in home inspections. Insurance claims for interior wall water damage frequently trace back to missing kickout flashing at the roof-to-wall termination.

Insurance Considerations for Roof-to-Wall Flashing

Roof-to-wall flashing damage from wind events typically presents as lifted or displaced step flashing pieces, separated apron flashing, or torn sealant at the wall-to-metal interface. Wind-driven rain can force water behind flashing that has even small gaps, causing significant interior damage. When documenting these areas for a claim, photograph the flashing from the roof side and, if possible, from behind the siding to show the wall leg condition. Note whether the siding has been in contact with the flashing without a drainage gap, as this is a pre-existing condition that exacerbates storm damage. Xactimate line items for roof-to-wall flashing include step flashing, continuous flashing, and kickout flashing as separate entries, so measure each type independently.