Why This Joint Fails
A roof sheds water toward its edges. Where a roof slopes down alongside a wall, all the water running along that wall arrives at one corner at the bottom. If nothing turns it away from the wall, it pours down the face of the stucco or straight into the wall behind it.
Builders' guidance calls the roof-to-wall intersection one of the most vulnerable points on a house. A Pro Builder / IBACOS article calls it "the most vulnerable point for water intrusion," and the U.S. Department of Energy's Building America Solution Center warns that water in wall cavities can cause significant damage to sheathing, framing and insulation, along with mold.
Stucco makes it harder to see. Water behind stucco can do damage for years before it shows inside.
What the Code Requires
New Mexico adopts the 2021 International Residential Code with amendments through 14.7.3 NMAC.
Flashing at wall and roof intersections (R903.2.1). The IRC requires flashing at wall and roof intersections, changes in slope and roof openings, and it requires "a flashing ... to divert the water away from where the eave of a sloped roof intersects a vertical sidewall." That's the kick-out. Metal flashing must be corrosion resistant and at least 0.019 inch thick (No. 26 galvanized). New Mexico's amendment keeps those requirements and adds "approved reglets," grooves that hold counterflashing, as an option.
Step flashing (R905.2.8.3). Base flashing against a sidewall must be continuous or step flashing, at least 4 inches high and 4 inches wide, and must direct water away from the wall onto the roof or into the gutter.
Wall flashing (R703.4). The wall covering code also requires flashing at wall and roof intersections, applied so water can't get into the wall cavity.
Clean roofs. New Mexico's stucco amendment requires residual stucco to be removed from roof surfaces before it cures.
Why Stucco Should Stop Above the Roof
The code doesn't set a specific gap between stucco and shingles, but building-industry guidance does. JLC describes terminating stucco with a weep screed held 1 to 2 inches off the roof, and IBACOS recommends holding wall finishes at least 2 inches away from the roof surface to prevent wicking.
When stucco is run down into the shingles:
- Water running down the roof soaks into the bottom edge of the stucco and wicks up.
- The step flashing can't be inspected or replaced without breaking the stucco.
- Shingles can't be replaced along the wall without damaging the stucco.
The Kick-Out: Small Part, Big Job
A kick-out is a small piece of formed flashing at the bottom of the roof-to-wall line. It turns the water coming down along the wall out into the gutter or off the roof edge. The Building Science Corporation's Common Flashing Details calls it "a critical component" of step flashing and shows a version specifically for stucco.
Without one, JLC describes water "pouring over the wall area below" and remediations where sheathing and framing had rotted to grade.
Look at the bottom corner of any roof that runs alongside a stucco wall: over a garage, a porch or a lower addition. Staining, cracking, bubbling or soft stucco below that corner is the classic sign of a missing or failed kick-out.
Signs of Trouble
- Stains or streaks on the stucco below the bottom of a roof-to-wall line.
- Cracked, bubbling or crumbling stucco in that area.
- Stucco running directly into the shingles with no gap.
- No visible kick-out at the eave end of the wall.
- Interior stains on the wall below the roof-to-wall line, or water at a window below it.
- Soft or stained ceiling where a lower roof meets a two-story wall. See ceiling water stains.
How a Repair Is Done
The order is the same as any flashing repair: fix the water path, then the finish.
- Open the stucco at the roof line. The stucco is cut back far enough to reach the flashing and the paper behind it.
- Check what's behind it. Any rotted sheathing or framing is repaired.
- Rebuild the water path. The roofing is lifted along the wall, new step flashing is woven in with each shingle, and a kick-out goes at the bottom. The wall's water-resistive barrier laps over the flashing, shingle-fashion.
- Terminate the stucco above the roof. A screed sets a consistent gap above the shingles.
- Patch and match the stucco. New lath and coats are tied into the existing stucco and the color coat is matched.
The DOE's guide to flashing roof-wall intersections in existing homes lays out the same sequence for retrofits.
Why reroofing usually touches the stucco. Step flashing that's buried behind stucco can't be pulled out without breaking it. A reroof is the right time to fix this joint properly. It's also why this repair takes a roofer and a stucco crew working together. Timberwolf does both flashing repair and stucco.
Flat Roofs and Parapets
On a flat roof, the same principle applies where the roof meets a parapet: the membrane turns up the wall and is lapped by the parapet's waterproof cover. That's covered in why parapet walls leak.