How to fix shingles that are lifting?

To fix shingles that are lifting, you need to determine whether they are lifted due to broken sealant or physical damage. If the shingle is intact but the adhesive strip has failed, you can reseal it. Wait for a warm, calm day when shingles are flexible, ideally above 60 degrees Fahrenheit. Gently lift the affected shingle, being careful not to crack it, especially in cold weather. Clean any debris from underneath. Apply three quarter-sized dabs of asphalt roofing cement or roofing sealant in a triangle pattern under the lifted area, just above the factory sealant line, not at the very edge. Press the shingle down firmly for 30 seconds to ensure good contact. For best results, place a brick or heavy board on top for several hours, or hand-seal with additional cement if the factory seal will not reactivate. If the shingle is creased, torn, or has a broken mat from wind bending, sealing alone is insufficient because its structural integrity and wind rating are compromised, and it should be replaced entirely by carefully removing nails from the course above and sliding a new matching shingle in. If many shingles across the roof are lifting, it indicates widespread seal failure due to age or poor installation, and a professional inspection is needed to determine if replacement is required.