Adding a drip edge to an existing roof that lacks one is technically possible as a retrofit project, but it requires careful labor. A roofer must gently lift the edges of existing shingles and pull old nails along the perimeter to slide the new metal flashing into place. However, because older asphalt shingles become brittle and prone to cracking when lifted, many contractors advise against retrofitting unless the roof is being re-shingled, ensuring the waterproofing integrity of the system remains intact.
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