My friend is having a house built. Slab is poured, it's framed in, has the electrical, ductwork and roof. We went out to look and saw the roof had "buckles" or waves in it. There was another house like it, in the same stage of build, in the same new subdivision. I let her know that was irregular, at least. But I don't know if this resulted from the decking being installed wrong, or being installed then a day or 2 later the shingles got nailed on, possibly over moisture? She has a meeting with the builder in the morning.
Buckling shingles could be caused by 1) lack of ventilation in the attic, 2) improper installation of the roof sheathing, 3) improper nailing of the shingles, or 4) wrong type vapor barrier.
1) If the attic is extremely hot, the shingles will buckle, especially if they are not nailed correctly.
2) If the roof sheathing isn’t nailed correctly or doesn’t have the correct spacing (gaps) between sheathing panels, they could expand and cause buckling, which would “telegraph “ through to the roof shingles.
3) if not enough nails are used or if the nails are in the wrong location, the shingles could buckle.
4) if a “rag” type vapor barrier was used, it could buckle if it got wet.