A customer wants to re-roof over an existing layer of 3-tab shingles. The deck shows no rot, but the existing shingles have cupping. What is the correct approach per best practices?
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A
Install new shingles directly over the cupped layer
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B
Tear off the existing layer before installing new shingles
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C
Nail down the cupped shingles flat before overlaying
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D
Apply roofing cement to the cupped areas and proceed with overlay