Two Existing Shingle Layers, Soft Decking, and a Cheap Overlay Request
A 1,850-square-foot single-story house has a 5:12 gable roof with two layers of aged three-tab asphalt shingles. Hail has caused granule loss and bruising. The homeowner wants the cheapest option: install new 30-year architectural shingles directly over the existing two layers, replace only the obviously soft decking, and reuse the old drip edge. The deck is 1/2-inch OSB; when you walk it, you find soft spots near the valley, at the chimney, and along the north eave. There is one ridge vent but no soffit vents; the attic has batt insulation and no baffles. The chimney flashing is step-flashed but rusted; the valley is woven. The homeowner also wants to add a skylight above the bathroom. The contract is for a reroof only and does not mention decking, ventilation, or flashing.
1. Can the contractor install new architectural shingles over the two existing layers? What does the adopted residential code require?
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No. The adopted IRC limits reroofing over existing coverings to not more than one existing layer; with two layers, a full tear-off is required before installing new shingles. The contractor cannot simply replace soft spots and overlay. The 5:12 slope is acceptable for asphalt shingles, but that does not cure the layer limit. Because the existing roof is being removed, the contractor must also inspect and repair the deck, replace deteriorated sheathing, and renail the deck to the current schedule. The contract should be revised to include tear-off, a decking allowance, and disposal before work starts. The homeowner should be told in writing why the cheap overlay is not code-compliant.
2. What decking, underlayment, flashing, and ventilation corrections are required before the new roof is installed?
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Required corrections: replace soft or delaminated OSB at the valley, chimney, and eave; renail sheathing; install new underlayment over the entire deck; install new drip edge at eaves and gables; replace rusted step flashing and counterflashing at the chimney; and install new valley flashing rather than reusing the woven valley. Ventilation is deficient: one ridge vent without soffit intake will not work; add soffit vents and baffles to maintain the insulation gap and provide balanced intake and exhaust. The skylight needs a curb, proper flashing, and a separate code check; it is not included in the reroof contract. All changes should be documented by change order with price and schedule impact.
3. How should the contractor handle the homeowner's request to add a skylight during the reroof?
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Treat the skylight as a separate scope. Confirm the rough opening, curb height, flashing kit, and whether the bathroom ventilation is adequate. Check the IRC for skylight and roof window requirements and obtain a permit if the local jurisdiction requires one. Do not cut the roof without a signed change order that addresses framing, insulation, interior finish repair, and waterproofing. If the homeowner declines, exclude it clearly in writing. The original contract should not be interpreted to include the skylight, and the contractor should not perform extra work on a handshake.