Tab shingles, commonly made from asphalt, are flat and uniform in shape but have cutouts or tabs that give the appearance of individual shingles. Oil canning is a visual effect that looks like waviness or slight buckling across the surface of these shingles. This happens because the shingles, which are designed to lay flat, can expand and contract due to temperature changes, moisture, or installation issues like uneven nailing or insufficient decking support. Oil canning does not mean your roof is leaking, but it can detract from its overall appearance and potentially indicate underlying problems with ventilation or installation.
To check for oil canning yourself, start by inspecting the shingles on a dry, sunny day to better see the waviness; watch for any loose nails or shingles that lift easily. Ensure your attic is properly ventilated to reduce heat buildup, which can cause shingles to warp. If the buckling is severe or widespread, it’s best to call a professional roofer. When consulting a contractor, ask if they plan to check the roof decking for flatness and if they use proper nailing patterns to allow for slight shingle movement. Also, inquire about ventilation improvements that might prevent future oil canning. These questions help guarantee that any repair or replacement work addresses both cosmetic and structural concerns without voiding warranties.