Chimney Flashing and Deck Deflection on a 1978 Ranch
A 1978 single-story ranch has a 4:12 gable roof, 18 squares of 3-tab asphalt shingles installed in 2006 over the original 3/8-inch plywood deck. Rafters are 2x6 at 24 inches on center; deck panels are fastened with 8d common nails and H-clips, and visible sagging occurs between rafters on the south slope. The homeowner reports staining on the ceiling within 12 inches of a 60-inch-wide masonry chimney on the north slope. The chimney has a galvanized pan flashing that is rusted through at the corner, no cricket, and no counterflashing; the shingles were woven into the chimney rather than step-flashed. The homeowner's contractor proposes a full tear-off and redeck, citing 'soft deck' and 'failed flashing.' A second contractor proposes sealing the flashing with mastic. The homeowner wants to know which is right and whether insurance should pay.
1. Identify the flashing defects and explain how water is likely entering at the chimney given its width and the 4:12 roof slope.
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The chimney is 60 inches wide, well past the 30-inch threshold at which model codes require a cricket on the upslope side. Without a cricket, runoff strikes the chimney head-on, ponds against the masonry, and has only the pan flashing to stop it. Three defects combine: the galvanized pan is rusted through at the corner, a direct opening; there is no counterflashing, so the top edge of the flashing is not let into a reglet and water can get behind it; and the shingles are woven across the chimney face instead of step-flashed, so there is no course-by-course diversion. On a 4:12 slope, water moving down the north slope is turned sideways at the chimney; without step flashing, capillary action and wind-driven rain enter at every shingle course. The rust hole explains the staining within 12 inches of the chimney. A mastic seal is not a repair because it cannot restore the missing counterflashing or the cricket and will fail as the pan continues to corrode. The correct repair is to remove shingles around the chimney, install a cricket, new pan and counterflashing, step-flash each course, and add ice-and-water shield at the intersection.
2. Is the deck deflection by itself a reason to require a full redeck? Explain what you would inspect and what threshold you would apply.
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Deflection between 24-inch rafters does not by itself prove the deck is unusable. 3/8-inch plywood is commonly rated for 24-inch support spacing, and some visible sag is normal at that span. I would inspect from the attic and test with an awl or probe: look for delamination, rot at penetrations and the chimney, fastener withdrawal, and cracked or broken panels. I would pull a string line to measure deflection and check the panel stamp for span rating. A full redeck is justified only if a substantial portion of the deck is delaminated, rotted, or unable to hold fasteners; isolated soft panels are replaced individually. When re-roofing, many jurisdictions require a minimum 15/32-inch or 1/2-inch deck or an overlay system approved by the manufacturer, so verify the local amendment. The contractor's 'soft deck' claim should be documented panel by panel, not generalized from the south slope sag. If the deck is sound, a flashing repair with limited shingle removal is appropriate and far less costly than a tear-off.
3. How should the inspection report classify the two contractor proposals and the homeowner's insurance question?
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The report should separate three issues. First, the flashing failure is a construction defect: no cricket, no counterflashing, rusted pan, and woven shingles. Long-term corrosion and improper original detailing are maintenance or installation issues, not a sudden storm loss. Second, the deck sag is a separate condition that needs its own evaluation; it does not convert the flashing defect into a full-replacement claim. Third, the mastic proposal is inadequate and should be identified as a temporary sealant that will not address water behind the flashing. If the deck proves sound, the covered repair is limited to the chimney area; if the deck is deteriorated across the roof, replacement may be technically necessary, but the cause is long-term moisture, not the flashing alone. On coverage, I would not make the decision for the insurer; I would state cause and origin, distinguish pre-existing deterioration from any storm-related opening, and note that the rusted pan and missing cricket pre-date the claimed loss. A full tear-off may be technically justified only if the deck inspection supports it.