Chimney Leak, Missing Cricket, and a Valley Decision in Ice-Dam Country
A homeowner reports a ceiling stain at the brick chimney after three days of wind-driven rain from the northeast. The roof is a 7/12 gable, and the chimney is 36 inches wide, centered on the slope, with no cricket. The existing step flashing is rusted and the brick has a reglet but no counterflashing. The roofer plans to reuse the reglet, install new 5-inch by 5-inch step flashing, and seal the top edge with polyurethane caulk. On the same roof, a 14-foot valley between a 6/12 and a 10/12 slope currently has an open 24-gauge metal valley. The contractor wants to remove the metal and weave the new laminated shingles because 'it looks cleaner.' The home is in a region with frequent ice dams and 30 psf snow load.
1. What is wrong with the proposed chimney flashing detail, and what is the correct sequence?
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The chimney is 36 inches wide, so it needs a cricket on the upslope side to divert water around it; caulk and step flashing alone will not handle the concentrated flow. Reusing the reglet without installing counterflashing leaves the top edge of the base flashing exposed to wind-driven rain. Caulk is a maintenance item, not the primary water barrier.
The correct sequence is to install ice-and-water shield tight to the chimney, then base flashing at the roof-to-masonry joint, then step flashing woven with each shingle course on the sides. Step flashing should have a roof leg and a wall leg, with the shingle overlapping the roof leg and the next step piece overlapping the shingle. Counterflashing should be inserted into a clean reglet at least 1 inch deep and sealed, with the lower edge lapping over the base flashing. The cricket should be framed and covered with metal or membrane, flashed into the chimney, and integrated with the field shingles. The top edge of the counterflashing should be sealed, but the bottom must remain free to drain.
2. Should the open metal valley be replaced with a woven valley? Explain the trade-offs.
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In a region with frequent ice dams and a 30 psf snow load, removing a sound 24-gauge open metal valley to weave shingles is usually the wrong trade. Open metal valleys shed water and ice melt quickly, are easier to inspect, and do not depend on shingle interlacing at the most concentrated flow point on the roof. A woven valley can look cleaner, but it creates more layers, more nails near the valley center, and more opportunities for water to back up under shingles during ice damming.
If the manufacturer specifically approves a woven valley for these slopes and the ice-dam detail is robust, it can perform, but the burden is on the installer to prove it. The safer choice is to keep or replace the open metal valley: 24-gauge metal, 16 to 20 inches wide, with about 10 inches exposed, hemmed edges, and fasteners at the edges rather than through the center. Install ice-and-water shield beneath the valley and carry it up the slopes. Do not nail through the valley pan, and do not leave the metal loose enough to telegraph through the shingles.
3. How would you diagnose the actual leak path before doing the repair?
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Start with the leak pattern and the weather direction. A northeast wind-driven rain stain points to the chimney's northeast face, the reglet, or a step-flashing lap that opens under pressure. Inspect the reglet for missing counterflashing, cracked mortar, and failed sealant; check the cricket area for ponding and for shingles that were run directly into the brick. Look for rusted step flashing, nails through the flashing, and shingle courses that were not interlaced.
Inside the attic, trace the water path on the deck and framing rather than assuming the stain is directly below the entry point. Use a hose test in dry weather, starting low and working up, and isolate the chimney from the valley. Check the valley for nail penetrations, backwater at the hem, and ice-dam evidence. Photograph each defect before repair. The repair should address the cricket, counterflashing, step flashing, and valley as one water-management system, not as isolated caulk joints.