Heavy rains can pour thousands of gallons of water onto a home’s roof in a single storm. In multi-level house designs where roofs intersect walls, this roof-wall intersection will channel much of this water to drain off the roof and usually into a gutter. If sidewall flashing is lacking or inadequate, water can leak into the wall and cause serious water damage. In big storm events, rainwater can often overflow the gutter and stream down the walls. Diverters are sometimes fashioned onsite in an attempt to direct this water into the gutters. If undersized, these diverters are not very helpful. If not properly integrated with the WRB (water-resistant barrier, e.g., house wrap) and cladding, they can do more harm than good by allowing water inside the wall cavities. The result can be significant damage to wall sheathing, framing, insulation, and mold inside the wall cavities. While older wood siding would show evidence of this water intrusion by peeling paint, new wall claddings like fiber cement, vinyl siding, and brick veneer can mask the evidence for years.
Flashing is required at roof-wall intersections (step flashing) to divert water away from where the eave of a sloped roof intersects a vertical sidewall (kick-out flashing). Where flashing is metal, the metal shall be corrosion resistant with a thickness of not less than 0.019 inches (26-gauge galvanized sheet) (2018 IRC R903.2.1). To be effective, all flashing must be integrated with the roof and wall drainage planes shingle-fashioned, where the top layer of the WRB or flashing laps over the bottom layer to prevent water from draining behind the bottom layer.
Kick-out flashing directs rainwater into rain gutters, where it can be carried away from the structure. Kick-out flashing also referred to as diverters, can be fabricated on-site using sheet metal, but these can be undersized and may have unsealed seams that allow leakage. Prefabricated kick-out flashings are available as seamless, molded plastic pieces or metal with welded seams.
These materials would be installed by roofers in coordination with house wrap and siding installers. This task should be included in the contract for the appropriate trade, depending on the workflow at the specific job site.
Step flashings and kick-out diverters are required in the 2009 and 2012 IRC (R703.8) and 2015 and 2018 IRC (R703.4; R903.2.1). See the Compliance tab.

How to Install Sidewall Flashing and Kick-Out Diverters — On Homes with Rigid Foam Insulation Sheathing

1. Install the drip edge and roofing underlayment over the roof deck and lap the underlayment up the sidewall and over the rigid foam insulation a minimum of 8 inches (Figure 2).
2. Install the shingle starter strip at the roof eave in accordance with the roofing manufacturer’s instructions (Figure 3).
   1. Place the seamless, one-piece, non-corrosive kick-out diverter as the first piece of step flashing.
   2. Slide the kick-out diverter up the roof plane until the starter trough stops at the shingle starter strip. The diverter must be flat on the roof and flush with the sidewall (Figure 3).
   3. Fasten and seal the diverter to the roof deck and starter strip. (Do not fasten it to the sidewall.)
3. Place the first row of shingles and the next section of sidewall flashing over the up-slope edge of the diverter, lapping a minimum of 4 inches over the diverter (Figure 4). Sidewall, and flashing height requirements, should be determined by a design professional and local building codes.)
4. Install the remaining sidewall flashing, appropriate counter flashing, and shingles in accordance with the manufacturer’s instructions (Figure 5).
5. Apply self-adhesive flashing over the top edge of the wall flashing, diverter, and rigid foam insulation (Figure 6).
6. Apply construction tape over the self-adhered flashing (Figure 7).
7. Apply siding over the rigid foam insulation.

How to Install Sidewall Flashing and Kick-Out Diverters — On Homes with House Wrap over OSB or Plywood Sheathing

1. Apply drip edge and roof underlayment over the roof deck (Figure 8). Continue lapping up the sidewall and over the weather-resistive barrier (in this case, house wrap) a minimum of 6 inches. A good construction practice is to leave a 1-inch gap between the vertical wall and fascia to accommodate the house wrap below the roof line. Install the shingle starter strip at the roof eave in accordance with the roofing manufacturer’s instructions (Figure 9).
   1. Place the seamless one-piece non-corrosive kick-out diverter as the first piece of step flashing.
   2. Slide the kick-out diverter up the roof plane until the starter trough stops at the shingle starter strip. The diverter must be flat on the roof and flush to the sidewall.
   3. Fasten and seal the diverter to the roof deck and starter strip. (Do not fasten it to the sidewall.)
2. Place the first shingle and next section of sidewall flashing over the up-slope edge of the diverter, lapping a minimum of 4 inches over the diverter, as shown in Figure 10. (The sidewall flashing height requirement should be determined by a design professional and local building codes.)
3. Install the remaining sidewall flashing, appropriate counter flashing, and shingles in accordance with the manufacturer’s instructions (Figure 11).
4. Apply self-adhesive flashing over the top edge of the wall flashing, diverter, and house wrap (Figure 12).
5. Install the house wrap. Cut the house wrap to fit over the self-adhesive flashing and sidewall flashing (Figure 13). Note that these subsequent layers of house wrap, shown in Figure 13, will be installed shingle-fashion over the roofing underlayment, kick-out flashing, and base flashing. If house wrap and roofing are installed by different trades, it is important to coordinate this effort to maintain the drainage plane.
6. Apply siding over the house wrap.