Asphalt shingles sometimes buckle slightly, and in an irregular pattern, due to moisture in a the materials of a new roofing system. The wetness gets absorbed by the felt underlayment, causing the felt to wrinkle. This then telegraphs to the shingles above. But the moisture evaporates as the materials reach equilibrium with the the surrounding air, and the shingles settle back down flat.
However, a more pronounced buckling in a line running up the roof, like in the photo above, is caused by buckling of the edges of the plywood or OSB roof sheathing, due to water intrusion or extremely high humidity in the attic. An 1/8” gap is specified by manufacturers between sheets of plywood that are nailed side-by-side over a shared top chord of a roof truss or a rafter. If this requirement is ignored and the sheathing is butted tight, the wood has nowhere to go when the moisture makes it swell, except to curl up along the shared seam.
A common cause of high humidity in an attic is lack of ventilation, which can be caused adding insulation that covers the soffit vents or lack of soffit vents and/or ridge vents altogether. A clothes dryer that terminates into the attic, or has vent through the roof that has become disconnected in the attic, is another source of water vapor and heat. And, of course, a roof leak can spread water under felts that sometimes migrates along the roof sheathing.
Eliminating the moisture cures most buckling problems. It may be necessary to wait for the materials to stabilize before determining whether any repairs or replacement is needed.
To learn about two other visible roof problems and their cause, see our blog posts What causes roof shingles to curl up at corners?
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To learn more about roofs and attics, see these other blog posts:
• Why is my roof sheathing sagging between the trusses?
• Why is granule loss a problem for an asphalt shingle roof?
• What are the mistakes to avoid when doing attic improvements?
• What causes shingles to buckle along a line on the roof?
• What causes leaks at a fake roof dormer?
• What causes a sagging roof ridge line?
• What causes bubble-like blisters in a built-up and gravel roof?
• Why does it cost so much more to replace a steep roof than a low slope roof?
• What is "ponding" on a flat roof?
• Is an attic required to have a light by the building code?
• How can I inspect my roof for hurricane damage?
• Why is premature curl of roof shingles a problem?
• How can I tell if a roof has more than one layer of shingles?
• What are the common problems with attic insulation?
• What is the life expectancy of an asbestos cement shingle roof?
• What's the average lifespan of a roof?
• Why is it a mistake to replace a roof and not replace its flashings?
• Why is there no attic access hatch in the house?
• What is the building code requirement for an attic access hatch, scuttle, or door?
• Does a roof with multiple layers of shingles last longer?
• What can I do to prevent roof leaks?
• Are roof trusses better than roof rafters (stick framing)?
• Why is a popped nail in a shingle roof a problem? How do I fix it?
• What are the most common problems with wood roof trusses?
• What causes a lump or dip in the roof?
• If my roof is not leaking, why does it need to be replaced?
• How can I be sure my roofing contractor got a permit?
• How many layers of roofing are allowed on a home?
• What are the dark lines running parallel to shingles on my roof?
• Can metal roofing be used on a low slope/pitch roof?
• How can I make my roof last longer?
• What are the warning signs of a dangerous attic pull-down ladder?
• How can I find out the age of a roof?
• Should I buy a house that needs a new roof?
• Should I buy a house with an old roof?
• What are those metal boxes on the roof?
• What does "lack of tab adhesion" in an asphalt shingle roof mean?
• Why do roof edges start leaking?
• Why do my dormer windows leak?
• Do home inspectors go on the roof? Do they get in the attic?
• Should I put gutters on the house?
• How much of a roof truss can I cut out to make a storage platform in the attic?
• What's the difference between an "architectural" and a regular shingle roof?
• What does a home inspector look for when examining a roof?
• Do stains on the ceiling mean the roof is leaking?
• How can I tell if the house needs a new roof?
• Why does my homeowner's insurance want a roof inspection?
• What are the hazards to avoid when going into an attic?
Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.