A leak where a roof meets a wall almost always traces to the flashing at that joint. Along a sloped side, small pieces of step flashing should be woven into every shingle course with their upright legs tucked behind the siding and its weather barrier. Where the top of a roof dies into a wall, a single headwall (apron) flashing does the same job. When those pieces are missing, too small, reused and rusted, or sitting on top of the siding, water runs behind the wall and rots sheathing for years before a stain appears inside. This page is general information; your roofer and building department make the final call.
On this page: Signs · Causes · Ground checks · Repairs · Code basis · When to call
Signs of a failed roof-to-wall flashing
- Stains on an interior wall or ceiling below where a lower roof meets a second-story wall or dormer.
- Swollen, stained or soft siding along the roof line, worst at the lowest end.
- Peeling paint in a vertical stripe on the wall below that low end.
- Rotted sheathing or framing found when siding is removed.
Common causes
- The wrong kind of flashing. A single long L-shaped strip, or none at all, where step pieces belong.
- Step pieces that are too small to lap properly.
- The upright leg on top of the siding instead of under it, so water runs behind the metal.
- The weather barrier not lapped over the flashing, so water running down the wall can get behind it.
- Old flashing reused on a new roof and rusted through.
- Headwall flashing too short, or a top shingle course cut so short that the flashing’s roof leg is exposed.
- No kickout at the bottom end, a separate failure covered in our kickout flashing guide.
What you can check from the ground
- Look for caulk along the line where shingles meet the wall. A heavy bead usually means the flashing is being relied on, or is missing.
- Check clearance. Siding should stop a little above the shingles. Siding resting on the roof wicks water and rots.
- Walk to the low end of each roof-to-wall line and look for stained or swollen siding and peeling paint.
- Inside, check walls and ceilings under those lines after a storm.
A roofer confirms the source with a controlled water test, starting at the bottom of the intersection and working up.
How it should be repaired
| Repair | When it fits |
|---|---|
| Remove the lowest siding courses; add a kickout and new step flashing at the bottom end; re-lap the weather barrier | Damage is limited to the low end. |
| Remove siding along the whole intersection and reinstall step flashing course by course | Flashing is missing, undersized or on top of the siding. |
| Reset headwall flashing under the siding and weather barrier | Leak is at the top of a roof plane. |
| Replace rotted sheathing and framing | Rot found once the wall is open. |
Fixes that fail: caulking the siding to the shingles, face-nailing a new L-flashing over old step flashing, and tucking flashing behind siding without lapping the weather barrier over it.
Code and manufacturer basis
The 2024 IRC, section R905.2.8.3, says base flashing against a sidewall must be continuous or step flashing, at least 4 inches high and 4 inches wide, must direct water onto the roof or into the gutter, and, where there is siding, its vertical leg must be continuous under the siding. Section R905.2.8.4 has front-wall (headwall) flashing applied following the shingle manufacturer’s instructions. The 2021 IRC, section R703.4, requires corrosion-resistant flashing applied shingle-fashion at wall and roof intersections.
Owens Corning’s Duration instructions call for corrosion-resistant step flashing at least 4 by 4 by 8 inches and 2 inches wider than the shingle exposure. On a reroof, IRC section R908.5 requires rusted, damaged or deteriorated flashing to be replaced rather than reused.
When to call a roofer
Call when you see caulk doing the work of flashing, soft siding at a roof line, or a stain below a dormer or second-story wall. Integrity installs both roofing and siding, so the wall can be opened, flashed and closed by one crew without a gap between trades. Related guides: kickout flashing, chimney flashing and roof valleys, plus the full roof problems guide.
Book a roof-to-wall inspection
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred contractor with 650+ Google reviews. We show you photos of the flashing behind the siding before recommending a repair. Colorado Springs area: (719) 488-2800 or a free inspection. Denver metro: (303) 209-0152 or a free Denver inspection. Austin: (512) 610-5897 or a free Austin inspection. We answer the same business day.
Sources: 2024 IRC Chapter 9, sections R905.2.8.3, R905.2.8.4 and R908.5 (UpCodes); 2021 IRC Chapter 7, section R703.4 (UpCodes); Owens Corning Duration installation instructions (step flashing).
