Why does my new roof look wavy?
Short answer. A new roof can look wavy for harmless reasons, such as shingles that have not yet softened and sealed in warm weather or low-angle light that exaggerates normal variation. Persistent waves usually come from the structure below: decking of uneven thickness, sagging rafters, swollen sheets, or a roof installed over an old layer.
Normal, or not?
- Likely normal: slight unevenness right after a cool-weather install; shadow lines that look wavy in low morning light; small variation between shingle lots.
- Not normal: waves that line up with rafters or deck seams; a dip midway along a slope; a ridge line that sags in the middle; humps over particular sheets.
Where the waves come from
- Mixed decking. Replacement sheets of a different thickness from the originals create steps. New sheets should match the existing thickness or be shimmed.
- Swollen panel edges. OSB edges swell if they got wet or were butted tightly together.
- Sagging framing. Old rafters, undersized framing or failed truss connections let the deck dip between supports. That predates the new roof but becomes obvious under new, uniform shingles.
- Overlay. New shingles over old ones show every curl and patch underneath.
Roofing reveals these problems more often than it causes them, unless the deck should have been corrected during tear-off.
What to do
Take photos from the same spot at different times of day. Look in the attic for sagging rafters, cracked framing or gaps at the ridge. Then call your installer and ask whether the deck was checked and leveled during tear-off. A structural sag needs a framer or engineer; a decking problem may fall under the workmanship warranty. See OSB vs plywood roof decking and roofing over existing shingles.