11.2 Sidewalls, Headwalls, Kick-Outs, Counterflashing & Pitch Transitions

The Code Framework

Sidewalls With Different Claddings (R905.2.8.3)

• Siding: the vertical leg of the base flashing is continuous under the siding.
• Anchored masonry veneer (brick or stone): base flashing per this section plus counterflashing.
• Exterior plaster or adhered masonry veneer: base flashing per this section and the wall-cladding flashing rules in R703.6.3.

Step Flashing

The 2015 code accepts continuous or step base flashing. Shingle manufacturers generally specify step flashing at sidewalls, because separate pieces woven with each course let the roof and wall move independently and keep water on top of each course. Typical manufacturer practice:

1. Run the underlayment, and ice barrier where used, a few inches up the wall.
2. Install each step flashing piece so it laps the piece below and sits on top of the shingle course below. It is covered by the next shingle course.
3. Nail each piece to the roof deck only, near the top edge where the next course covers it. Do not nail into the wall.
4. Pieces must be at least 4 × 4 inches (R905.2.8.3). Long enough to lap the piece below by the manufacturer's minimum.
5. The water-resistive barrier (house wrap or felt) laps over the vertical legs, and the siding covers them. Keep siding a small distance off the shingles so it does not wick water, following the siding maker's clearance.

Kick-Out (Diverter) Flashing

Where a roof eave dies into a sidewall that continues past it, such as a garage roof against a two-story wall, water running down the step flashing reaches the wall at the eave. Without a diverter, it runs behind the siding and rots the wall. R903.2.1 requires a flashing that diverts water away at that point:

• Install a kick-out at the bottom of the sidewall step flashing, before the siding goes on, so it throws water out into the gutter or away from the wall.
• Seal and lap the WRB over its upper flange, as the kick-out manufacturer directs.
• One-piece molded or soldered kick-outs resist leaking better than field-bent ones.

Headwall (Front Wall) Flashing

Where a roof slope runs up to a wall, as at the top of a porch roof against a house:

• Install a continuous apron flashing over the top shingle course, with a vertical leg up the wall and a horizontal flange out over the shingles, per the manufacturer (R905.2.8.4).
• The WRB and siding lap over the vertical leg. At masonry, add counterflashing.
• At the corners where a headwall meets a sidewall, wrap the apron around and integrate the step flashing, so no raw joint faces uphill.

Counterflashing at Masonry

Base flashing against brick or stone needs counterflashing (cap flashing) over its top edge:

• Reglet (cut-in) method: cut a groove into a mortar joint, insert the bent edge of the counterflashing, wedge it, and seal it with an appropriate sealant. On sloped walls, step the counterflashing to follow the mortar courses.
• Surface-mounted: a termination bar or surface counterflashing with a sealant lip, fastened to the masonry. It depends on sealant maintenance.
• The counterflashing laps over the base flashing so water cannot get behind it, while the two pieces can still move separately.
• Cap flashing is corrosion-resistant metal at least 0.019 inch thick (R905.2.8.1).

Changes in Slope, Curbs, and Platforms

PSI's outline includes "install roof-to-wall transitions, curbs, other platforms, and pitch transitions." Flash all of these under R903.2.1:

• Pitch transitions (for example, from 12:12 to 4:12 on a gambrel, or a shingled slope meeting a low-slope porch): use metal transition flashing, or run underlayment and membrane continuously across the break so the upper material laps the lower. Follow the shingle and membrane manufacturers' instructions for the break.
• Curbs (skylights, hatches, HVAC): build curbs high enough to flash, and wrap them with underlayment or membrane. Install base flashing and counterflashing or the unit's flashing kit (Section 11.3).
• Platforms and decks on roofs: support them on flashed curbs or sleepers so water drains under them, and keep the roof membrane continuous.

Diagnosing Wall Leaks

• Stains below a sidewall's lower end: usually a missing kick-out.
• Leaks along a sidewall: often step flashing lapped backward, nailed through the wall leg, siding down on the shingles, or a WRB behind the flashing instead of over it.
• Leaks at a headwall: often missing apron flashing or siding that is not lapped over it.