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WHY YOUR ROOF SHINGLES ARE WAVY OR BUCKLING
Buckling shingles look like something is underneath the shingles pushing them upward. You also may have curling shingles, where the center of the shingle looks concave and the edges turn up. Both issues are noticeable from ground level and require the attention of a qualified contractor. A few culprits cause shingles to look wavy or rippled, including problems with the plywood or felt underneath the shingles, issues with expansion in extreme temperatures, misaligned shingles, or just generally poor craftsmanship.
Improper Framing or Sheathing
Sheathing is a series of wooden 4 foot by 8 foot rectangles, often made of OSB or plywood, that carpenters or roofers attach to the house’s frame (joists and trusses). This layer of wood is used to attach the roof’s shingles. Ripples can happen if the sheathing is installed without a gap between the boards to allow for expansion and contraction, or if the builder left the sheathing exposed to the elements for too long without covering it with a protective underlayment. If this is the problem, look for ripples spaced evenly 4 to 8 feet apart (to match the spacing of the plywood).
If the plywood beneath the shingles is fastened improperly, it means the fasteners missed the framing so nothing is holding the plywood down and it could warp. Another reason why sheathing boards can warp is if they were stored in a moist environment before being attached to your roof, or if the bare plywood was exposed to inclement weather and not shielded with plastic before the shingles were nailed down. Leaving these framing and sheathing issues unfixed is mainly a cosmetic issue and shouldn’t affect the integrity of your roof.
Damaged Felt Underlay
Typically, when completing a roof repair or replacing old shingles, a roofer will not remove more shingles than they can replace in the same day. This is because when the felt underneath the shingles is exposed to wet weather or morning dew, it will cause the felt to wrinkle. It’s important to note that you shouldn’t ever install a roof in the rain. The wrinkles will lay down flat if allowed to dry before first installing the shingles, but if the roofer stapled down the new shingles over wet felt, the new shingles will likely look wavy. Damaged felt underlay is mainly a cosmetic concern.
You may have curling or buckling shingles for a number of reasons, but the common denominator is moisture. Moisture is detrimental to a roofing system. If you had a roof replacement recently but kept the same roof decking, the wood may have absorbed moisture before the new roof was installed. Moisture can make the decking move and cause the shingles to buckle. The felt underlayment also could have absorbed moisture. This could make the underlayment wrinkle and push the shingles upward. Both issues require the attention of a professional — repair may involve replacing damaged shingles and wrinkled portions of the felt.
The most common cause appears to be movement in the roof sheathing with changes in moisture levels. When plywood or OSB sheathing picks up moisture, it expands. If the sheathing is properly gapped, then the gaps can close causing the shingles spanning the gap to buckle. If the sheathing is not gapped, the sheathing itself may buckle, especially with thin sheathing, 24 in. spacing, and significant changes in moisture. The lack of adequate attic ventilation can increase moisture cycling in the roof sheathing, adding to the problem.
Expansion
If a roofer installs shingles when it is close to freezing outside (40 degrees or below) and doesn’t leave a gap, you may see a wave from expansion. Unfortunately, the only solution to fix this problem is removing and replacing the shingles, otherwise it could shorten the lifespan of your roof.
Poor Craftsmanship
If you notice ripples like on a pond, that can be caused by improper stapling or nailing direction. Felt should always be stapled (or you can use plastic cap nails) and shingles nailed down in the direction the shingles are being laid. If shingles are not nailed down properly, they can be blown off in strong winds or storms and that can cause leaky roof problems for you in the future.
Attic Ventilation
Out of all the causes of buckling shingles, the most common and the most damaging reason is not enough ventilation in the attic. Hot air and condensation build up in the attic and make the shingles curl or buckle away from their proper place on the roof.
Consequences of Inadequate Ventilation
While curling or buckling shingles may be an outward symptom of an attic ventilation problem, a lack of proper airflow affects more than just the shingles. In the winter, an attic without enough ventilation can lead to ice dams. Hot air that escapes from your home rises to the attic and becomes trapped. It heats up the roof and causes snow and ice to melt, only to have the water refreeze on the eaves. This causes a backup of moisture that only serves to rot your roof deck and create the perfect environment for mold to grow in your attic.
In the summer, an overly hot attic makes your air conditioner work harder than ever to cool down your home. This causes the A/C to wear out faster than it should, and makes your cooling bills skyrocket. On top of these issues, ineffective attic ventilation means your roof will degrade faster than normal. The buckling and curling make it so the asphalt shingles don’t protect your home from precipitation like they should. The roof, and your entire home, will suffer as a result. In new construction, it is best to let the roof sheathing acclimate to local conditions before installing the roofing, although this is not always practical.
Another cause of buckling can be wetting of the felt paper, which will expand if it gets wet. If the felt paper is rained on, it’s best to let it dry out before installing shingles. Very cheap asphalt shingles swelling and buckling from moisture absorption, but this should not be the case with a name-brand shingle unless you got a defective batch.
What causes a lump or dip in the roof?
A sunken or buckled area in the roof is most easily visible when looking up the slope of the roof from the ground. Here’s four common causes:
Roof leak – Leakage of the roofing that has caused rot and partial collapse of the sheathing in the area of the leak is the #1 cause of a roof dip. It often occurs next to a roof penetration, such as a chimney or dormer, or at the edge of the roof, as in the photo above, and is easily verified by checking the area in the attic. The sheathing will be dark and discolored when viewed from below, with possible mold growth.
Warped sheathing – Uneven stresses between the plies of a sheet of plywood can cause it to warp at the edges over time. H-clips are installed at the center of the span of unsupported abutting edges to stiffen the them; but, if they are missing, damaged or installed off-center, buckling can occur. It is usually not a structural problem.
Roof impact – When a heavy object such as a tree branch drops on the roof, it will cause a depression in the area and likely some structural damage to sheathing and roof trusses or rafters underneath. In the photo below, the impact depression is accompanied by a small hole.
