What causes roof shingles to buckle?
Short answer. Shingles buckle when something underneath them moves or swells: decking that absorbs attic moisture, felt underlayment that wrinkled before the shingles went on, or a new layer laid over old, uneven shingles. Poor nailing and a hot, badly vented attic make it worse, and buckled shingles can lose their seal and lift in wind.
The main causes
- Deck movement. Plywood and OSB swell with moisture. If panels were installed tight without the recommended gap, the seams push up and the shingles over them form straight ridges.
- Wrinkled felt. Asphalt felt absorbs moisture and ripples if it gets rained on or sits exposed before shingling. Shingles laid over the wrinkles show them as waves. Synthetic underlayment largely avoids this.
- Roofing over old shingles. A second layer follows every curl and lump of the first. See roofing over existing shingles.
- Nailing errors. Nails driven crooked, too high or not flush let shingles shift and hump.
- Attic heat and moisture. Poor ventilation drives heat and moisture into the deck. See attic heat and shingles.
Buckling vs curling vs blistering
Buckling is a ridge or hump, often running in a straight line across several shingles. Curling is the edges or corners of individual shingles turning up or down from age and heat. Blistering is small raised bubbles in the surface. Each has a different cause, and an inspector will tell them apart from hail bruises, which an adjuster treats very differently.
Does it need fixing?
Mild buckling on a brand new roof sometimes settles as the deck dries out. Ridges that last through a season, or buckling with soft spots underfoot, mean the deck or ventilation needs attention. Buckling is not usually storm damage, so insurance generally treats it as a wear or workmanship issue rather than a covered loss.