6.3 Steep-Slope Flashing Details

6.3 Steep-Slope Flashing Details

Quick Answer: Asphalt field shingles shed water; flashings keep water out where the roof meets walls, chimneys, and pipes. CTS Domain 3 expects you to sequence step flashing, headwalls, crickets, and pipe boots so every lap sheds downslope through Illinois ice and wind.

Most steep-slope callbacks are flashing failures, not “bad shingles.” Learn the pieces, the weave with shingle courses, and the Illinois climate stresses that open tiny gaps into leaks.

Sidewall Step Flashing

Where a roof abuts a vertical sidewall (dormer cheek, higher wall, chase), use step flashing: individual L-shaped metal pieces installed with each shingle course.

Correct sequence:

1. Apply ice-and-water or underlayment up the roof and onto the wall as required
2. Set the shingle course
3. Place a step flashing piece over that shingle, vertical leg against the wall, base leg covering the shingle
4. Install the next shingle over the base leg of that step
5. Repeat up the slope—one step per course

Typical step size is about 8 inches by 8 inches (or manufacturer/code minimums), with enough length to lap the course exposure. The vertical leg must be long enough to be covered later by siding or by counterflashing. Never run a single continuous “step” substitute that is only face-caulked to the wall without weaving into courses—caulk alone is not the weather barrier.

Continuous Flashing

Continuous flashing (one long piece) appears in limited asphalt situations—sometimes along a headwall apron, roof-to-roof transitions, or manufacturer-approved details—but it is not a blanket replacement for step flashing on sidewalls. Exam distractors often show a continuous metal strip stuck to a sidewall with caulk and no steps; that detail fails when Illinois freeze-thaw splits the sealant.

Where continuous metal is used (for example, a headwall apron), it must:

• Lap onto the shingles downslope enough to discharge water onto the shingle surface
• Be counterflashed or integrated into the wall above
• Avoid reverse laps and unprotected fastener holes in the water path

Headwall Flashing

A headwall is where the top of a roof plane meets a wall (the high side of a dormer roof into a wall, or a lower roof into a story wall). Water running down the wall must hit metal and land on shingles, not behind them.

Typical headwall (apron) detail:

1. Complete shingles up to the wall
2. Install apron flashing over the shingles, vertical leg on the wall, base leg on the roof
3. Counterflash or integrate wall covering over the vertical leg
4. Ensure kick-out flashing where a headwall/sidewall dumps water at a wall corner so runoff enters a gutter, not the wall cavity

Missing kick-out flashing at the eave end of a wall-roof intersection is a frequent Illinois moisture intrusion path into sheathing and framing.

Chimneys: Steps, Counterflashing, and Crickets

Chimneys combine sidewall and headwall problems on three or four sides.

Sides: Step flashing woven with each course, then counterflashing cut into mortar joints (reglet) or surface-mounted with a receiver, overlapping the steps. Base flashing (steps) should not be the only metal buried in mortar without a counterflashing cover.

Front (downslope face): Apron flashing over the shingles below the chimney.

Back (upslope face): Critical. On chimneys 30 inches or wider (common IRC/CTS threshold), install a cricket (saddle)—a small peaked diversion roof—so water and ice cannot pond against the upslope face. Narrower chimneys may use a backer flashing / sheet metal pan that extends under upslope shingles and up the chimney, still counterflashed.

Illinois freeze-thaw expands moisture in masonry. Counterflashing driven into mortar joints must be re-secured when joints fail; surface-mounted receivers need compatible sealant maintenance. Never rely on tar “collars” alone around a chimney base.

Pipe Boots (Plumbing Jacks)

Pipe boots (neoprene or metal jack flashings) seal plumbing vents and similar round penetrations.

Integration rules:

1. Shingle the roof up to the low side of the pipe
2. Fit the boot over the pipe; the back (upslope) flange goes under the shingles above
3. The front (downslope) flange goes over the shingles below
4. Nail the flange in the headlap area per product instructions; seal only as directed
5. Ensure the rubber collar is sized to the pipe and not inverted or sliced open “to fit”

If a boot is installed with the entire flange on top of all shingles, water running from above goes under the flange onto the underlayment—an exam-classic defect. If the entire flange is buried under shingles on the downhill side, water cannot discharge onto the roof surface.

Replace cracked Midwest neoprene boots during reroofs; UV and ozone make old collars brittle after Illinois summers.

Other Penetrations and Skylights

Skylights and curb-mounted units need manufacturer pan flashings with step or continuous side pieces and head flashings that shed onto the roof. Follow the skylight maker’s asphalt kit—generic step flashing alone may not match the curb height. Electrical masts and furnace vents use specialized flashings with the same under/over shingle logic as pipe boots.

Illinois Wind and Freeze-Thaw Flashing Takeaways

1. Metal expansion: Long continuous runs need room to move; cracked solder or pulled fasteners open leaks after temperature swings.
2. Ice dams: Water backed upslope finds every unlapped step and every uncounterflashed chimney side—ice barriers at walls and valleys buy time but do not excuse bad metal work.
3. Wind: Loose step legs or unfastened boot flanges lift; nail flanges in designated zones and cover nails with the next shingle course.
4. Compatibility: Pair flashings and fasteners to avoid galvanic corrosion (for example, be careful mixing copper with steel in wet Midwest conditions).

Exam Application

When a Domain 3 item describes a leak at a dormer wall, think missing or reverse-lapped step flashing. When the leak is behind a chimney after a thaw, think missing cricket or failed counterflashing. When water appears around a plumbing vent after rain, think boot flange installed entirely on top of the shingles. Draw the water path in your head: every piece must lap so water stays on the exterior skin until it reaches the eave.