Asphalt Shingle Buckling — Causes, Prevention, and Solutions

What Shingle Buckling Looks Like From the Ground

Shingle buckling is one of the easier roof defects to spot from the street, once you know what you are looking at. The defining characteristic is a raised ridge or wave that runs in a straight line across the slope of the roof. The shingle surface is not flat — it has a visible hump, anywhere from a quarter-inch to over an inch in height, that travels in a straight path parallel to the ridge or perpendicular to the rake. From the right angle in low morning or afternoon light, buckled ridges cast a shadow line that makes them obvious even from a distance.

The straight-line pattern is the key diagnostic clue. A buckle follows the joint between two adjacent roof deck panels. Plywood and OSB panels are manufactured in 4-foot by 8-foot sheets, and those sheets are installed in staggered courses across the roof deck. When the panel edges push against each other — for any of several reasons we will cover below — the force has nowhere to go except up, and the shingles directly above the joint lift into a ridge. This is why you will rarely see a buckle running diagonally across a roof: the panel joints are either horizontal or vertical relative to the slope, so the buckles are too.

The buckle itself feels firm, not soft, when pressed. The shingles are being supported from below by the raised deck panel edge. In contrast, a soft spot in the roof deck — caused by rot or delamination — feels spongy underfoot because there is no support below. If you walk a buckled area and it feels rigid under your feet, the deck is sound and the problem is a joint spacing issue. If you feel flex or give, there is a structural problem that requires immediate attention and goes beyond the scope of a buckling diagnosis. See our guide on roof deck requirements for structural assessment criteria.

How Buckling Appears as a Roof Ages

Buckling can appear on a brand-new roof within the first year of installation — this is almost always a deck spacing or wet-deck installation issue. It can also develop gradually on an older roof as ventilation degrades, insulation is added to the attic floor without addressing the existing vent openings, or as successive years of moisture cycling accumulate stress in the deck panels. On a newer roof, the buckle may be sharp and pronounced. On an older roof where the shingles have softened over years of thermal cycling, the buckle may be a broad, gentle wave rather than a sharp ridge.

Shingles that have been buckled for multiple seasons develop a permanent set. The fiberglass mat in an asphalt shingle is flexible when new but becomes progressively less elastic as the asphalt binder oxidizes and the mat ages. A shingle that has been held in a buckled position for two or three summers will not lay flat even if the deck movement that caused the buckle is corrected. The mat has taken a permanent deformation at the fold point. Those shingles are compromised and should be replaced, because the fold point is a stress concentration where cracking is likely to initiate. Cracked shingles allow water into the roof system — which is the scenario we are trying to prevent by addressing buckling in the first place.

Why Shingles Buckle: The Four Primary Causes

Shingle buckling is a symptom of a problem in the system below the shingles, not a shingle defect. The shingle itself is doing exactly what physics requires — conforming to the shape of whatever is beneath it. To fix buckling permanently, the underlying cause must be addressed. There are four primary mechanisms.

1. Deck Panels Installed Without Expansion Gaps

The APA (Engineered Wood Association), which sets the technical standards for plywood and OSB in structural applications, requires a 1/8-inch gap between adjacent panels on the roof deck. This gap is not optional — it is a fundamental requirement of proper deck installation, and it is referenced in the installation requirements published by GAF, CertainTeed, and Owens Corning for their shingle products.

The reason for the gap is straightforward: wood panels expand when they absorb heat and moisture, and they contract when they dry out. In Georgia, a roof deck panel on the south-facing slope of a home can reach temperatures above 140°F on a summer afternoon. OSB — oriented strand board, the most common modern decking material — is particularly sensitive to moisture because it is manufactured from wood strands bonded with adhesive rather than continuous wood fibers. When OSB absorbs humidity from a hot, poorly ventilated attic, it can expand significantly across its face dimensions.

When panels are butted tightly together with no gap — a shortcut that some crews take to avoid the minor inconvenience of spacing — summer expansion has nowhere to go. The panels push against each other. The only release for that compressive stress is upward deflection. The panel edges lift, creating a ridge at every tight joint. On a production home with a full roof deck, a bad installation crew can create dozens of potential buckle points by installing panels without gaps. Some of those joints buckle in the first summer. Others may take several years of moisture cycling before the cumulative deformation becomes visible.

2. Moisture from Below: Attic Vapor Drive

Even correctly spaced deck panels can buckle if moisture is moving upward from the attic in sufficient quantity. This mechanism is called vapor drive — warm, humid air from inside the living space or the attic moves toward the cooler roof deck surface, and the moisture in that air condenses on or is absorbed into the wood panels. Over repeated seasonal cycles, the panels accumulate moisture, expand, and stress the joints.

In Georgia, this is a year-round concern rather than a winter-only problem. During the long humid summers, attic air can carry substantial moisture loads. If the attic is not adequately ventilated — meaning there is not enough airflow to exhaust warm, humid air before it contacts the deck — the deck panels absorb that moisture. The problem is compounded if the attic insulation has been upgraded without ensuring that soffit vents remain unobstructed. A thick layer of blown-in insulation can completely block soffit vent openings, eliminating intake ventilation and creating a sealed hot attic that drives moisture directly into the deck.

3. Wet Deck at Time of Installation

Installing shingles over a wet or damp deck is a direct cause of early buckling. When the deck is wet — from rain during a re-roofing project, from morning dew that has not dried, or from a deck that was stored improperly on site — the moisture trapped between the deck and the underlayment has nowhere to go once the shingles are installed. As the roof heats up in the days after installation, that moisture turns to vapor and creates pressure that can lift shingles off the deck surface and cause localized buckling.

This failure mode is particularly insidious because it happens quickly — sometimes within weeks of installation — and the homeowner naturally attributes the buckling to defective shingles. In reality, the shingles are fine. The installation crew installed them over a wet surface, which is an installation error. Proving this after the fact requires an inspection that documents the moisture content of the deck panels and assesses whether the buckle pattern corresponds to the trapped moisture distribution rather than to a ventilation or spacing problem. At 1 Source Roofing, we do not install shingles on a wet deck. Period. If rain delays a project, we wait for the deck to dry or we cover it with tarps until conditions allow a dry installation.

4. Shingles Installed Over an Old Roof Layer

Building codes in most Georgia jurisdictions allow up to two layers of asphalt shingles on a residential roof. Some homeowners choose a re-roof (adding a second layer over the existing shingles) rather than a full tear-off and replacement in order to reduce cost and speed up the project. When this is done correctly and the existing shingle layer is flat and sound, the result can be acceptable. But when the existing shingle layer has any waviness, curling, or deformation, the new shingles will conform to those irregularities rather than laying flat. What looks like buckling in the new shingles is actually the new layer telegraphing the defects of the old layer beneath it.

This is one reason 1 Source Roofing recommends full tear-off and deck inspection on every re-roofing project. A layer-over installation obscures the deck condition and eliminates the opportunity to address deck gaps, replace damaged panels, and inspect the ventilation system. If buckling appears on a roof that was installed over an existing layer, the diagnosis must account for both the deck condition and the existing shingle layer condition before a repair or replacement strategy can be developed.

Buckling vs. Curling: Two Different Problems

Buckling and curling are frequently confused, and the distinction matters because they have different causes and different remedies. Both produce a roof surface that is not flat, but the pattern and location of the deformation are different.

Buckling: Follows the Deck Joints

As described above, buckling produces straight ridges that track along deck panel joints. The deformation is in the body of the shingle — the shingle surface rises along a line that corresponds to the joint below it. The shingle edges are not necessarily affected; the buckling may be in the middle of a shingle field well away from the tab edges or the top edge of the shingle course. If you can draw a straight line through the raised area and that line corresponds to a plywood panel dimension (typically 4 feet or 8 feet from another joint), you are looking at buckling caused by deck movement.

Curling: Affects Shingle Edges and Corners

Curling is a shingle-level failure, not a deck-level failure. It occurs in two forms. Cupping is when the tab edges turn upward so that the shingle cross-section looks like a shallow U rather than a flat surface. Clawing is when the tab edges stay relatively flat but the middle of the shingle is raised, creating a reverse-curve profile. Both forms of curling are caused by differential drying and aging between the top surface and the bottom surface of the shingle.

As an asphalt shingle ages, the top surface loses granules and oxidizes, becoming less flexible. The bottom surface, which is protected from UV, ages more slowly. This differential aging creates internal stress that causes the shingle to deform toward the surface that is aging faster — the top. Curling shingles are a sign of age, granule loss, or manufacturing variability in the shingle's mat structure. A roof with widespread curling is near or at end-of-life. The shingles cannot be flattened or repaired — they must be replaced.

The diagnostic question is simple: do the raised areas follow straight lines across the roof field, or do they affect shingle edges and corners across the entire surface? Straight lines across the field indicate buckling. Edge and corner deformation distributed across the whole roof indicates curling. A roof can exhibit both simultaneously — if an older roof with a compromised ventilation system has both aged shingles that are curling and deck panels that are expanding, you may see a combination pattern. In that situation, replacement is the only solution. For more detail on signs that indicate replacement versus repair, see our guide to signs you need a new roof.

CertainTeed's Technical Bulletin on Shingle Buckling

CertainTeed has published a technical bulletin on asphalt shingle buckling that addresses the root causes from the manufacturer's perspective. The bulletin is available for reference at CertainTeed Asphalt Shingle Buckling Technical Bulletin (PDF).

The bulletin's core finding is consistent with what experienced contractors observe in the field: shingle buckling is almost never a shingle manufacturing defect. CertainTeed's position, based on field investigation of warranty claims, is that the vast majority of buckling complaints trace back to installation conditions — primarily inadequate deck spacing, moisture in the deck at the time of installation, and inadequate attic ventilation. This is significant for homeowners considering a warranty claim: if buckling appears on CertainTeed shingles and the investigation reveals that the deck spacing was inadequate or the attic ventilation does not meet published requirements, the warranty claim will be denied on the basis of improper installation conditions.

What the Bulletin Says About Deck Spacing

CertainTeed's bulletin specifically calls out deck panel spacing as a primary cause of buckling, citing the APA requirement for 1/8-inch gaps. The bulletin notes that this requirement is not unique to CertainTeed — it is a fundamental wood panel installation standard that predates shingle manufacturing standards. Contractors who install deck panels without gaps are violating both the APA standard and the shingle manufacturer's installation requirements simultaneously. If a claim is made on buckled shingles and an inspector finds tightly butted deck panels, the claim is denied on installation error grounds regardless of how old the shingles are or how expensive they were.

What the Bulletin Says About Moisture

The bulletin addresses both pre-existing deck moisture at installation and ongoing moisture vapor drive from the attic. On the installation side, CertainTeed's guidance is unambiguous: shingles must not be installed over wet or damp decking. On the ventilation side, the bulletin references the 1:150 ventilation ratio (1 square foot of net free area per 150 square feet of attic floor) and specifies that ventilation must be balanced between intake and exhaust. An attic with ridge vents but blocked soffit vents does not meet this requirement, even if the total vent area calculation on paper suggests adequate ventilation.

Ventilation Requirements to Prevent Moisture-Driven Buckling

Attic ventilation is the single most effective preventive measure against moisture-driven shingle buckling, and it is also one of the most commonly deficient systems in Atlanta-area homes. A properly ventilated attic keeps deck temperatures lower, removes moisture before it can accumulate in the OSB or plywood, and extends shingle life by reducing thermal cycling stress. The math is simple but the execution requires attention to both the quantity and the balance of ventilation.

The 1:150 and 1:300 Ratios

The IRC ventilation requirement is expressed as a ratio of net free ventilation area to attic floor area. The base requirement is 1 square foot of ventilation per 150 square feet of attic floor. If the attic floor has a continuous vapor barrier, that ratio can be reduced to 1:300 because the barrier limits moisture migration from the living space into the attic. Most Atlanta-area homes do not have a continuous vapor barrier on the attic floor — they have blown-in fiberglass or cellulose insulation directly on the attic floor without a vapor barrier underneath. Those homes are held to the 1:150 standard.

To calculate your attic's ventilation requirement: measure the square footage of the attic floor, divide by 150, and that is the minimum net free area required in square inches multiplied by 144. A 1,500-square-foot attic requires 10 square feet of net free ventilation area — 5 square feet at the soffit for intake and 5 square feet at the ridge for exhaust. Net free area is not the same as the physical dimensions of the vent — it accounts for the obstruction of the louvers, screens, and baffles that cover the opening. Every vent manufacturer publishes the net free area of their products.

Balanced Ventilation: Intake and Exhaust

Total vent area is only half the equation. The ventilation must be balanced — approximately equal intake area at the soffit and exhaust area at or near the ridge. This balance is what creates the stack effect: cool outside air enters at the low soffit vents, heats up as it moves through the attic, rises, and exits at the ridge vents. This convective flow is continuous and passive — it requires no mechanical assistance and operates whenever there is a temperature differential between the attic and outside air.

An attic with generous ridge venting but blocked or inadequate soffit venting does not achieve this stack effect. Instead, the ridge vents may draw air in from outside (reverse-stacking), creating turbulent, inefficient airflow that fails to exhaust attic moisture. The most common soffit vent obstruction we find during Atlanta inspections is insulation installed too close to the eave, which buries the soffit vent openings. Attic baffles — cardboard or foam channels that maintain a clear airway between the insulation and the roof deck — prevent this problem, but they are frequently omitted during insulation upgrades. If you have added attic insulation in the last ten years without confirming that baffles are installed at every rafter bay, the soffit ventilation for those bays may be compromised. For comprehensive guidance, see our page on underlayment and attic moisture control.

Power Ventilation and Its Limitations

Powered attic ventilators — electric fans that exhaust attic air — can supplement passive ventilation in homes with structurally limited vent area. However, they introduce a complication: if the powered fan runs during heating season and the home is not well air-sealed, it can depressurize the attic and pull conditioned air up through ceiling penetrations, increasing heating costs and introducing warm, humid interior air into the attic. In Georgia, where cooling loads dominate the annual energy budget, this is less of a concern than in northern climates — but it remains a reason to ensure that powered ventilation supplements rather than replaces adequate passive ventilation capacity. Powered fans also require maintenance and have finite service lives. A passive ventilation system that is properly sized and balanced will outlast the roof.

Deck Spacing Requirements: The 1/8-Inch Gap

The 1/8-inch expansion gap between adjacent deck panels is not a guideline — it is a requirement published by the APA and incorporated by reference into the installation standards of all major shingle manufacturers. Getting it right requires a deliberate process at the time of installation, because butting panels tightly is the path of least resistance for a fast-moving crew.

On a full tear-off and re-deck project, 1 Source Roofing crews use spacers — small blocks or purpose-made plastic clips — to maintain the 1/8-inch gap at every panel joint. The spacers are placed before the panel is nailed, confirming the gap before fastening. This takes an additional few seconds per panel but eliminates the buckling risk entirely. When the spacers are removed after nailing, the gap is confirmed visually before the underlayment is installed.

OSB vs. Plywood: Moisture Sensitivity

OSB is more moisture-sensitive than plywood and requires the 1/8-inch gap even more critically. Plywood is a cross-laminated product — its alternating grain structure limits expansion in any single direction. OSB is manufactured from wood strands oriented primarily in one direction per layer, and its expansion under moisture is more pronounced in the face dimension than plywood's. An OSB panel that absorbs moisture from a poorly ventilated attic can expand more than 1/8 inch across its 4-foot dimension under extreme conditions — meaning that even a correctly spaced deck can experience joint stress if the attic moisture load is severe enough.

This does not mean that correct deck spacing is insufficient — it means that deck spacing and ventilation are complementary requirements, not alternatives. A deck with correct spacing and adequate ventilation will not buckle. A deck with correct spacing but inadequate ventilation may experience joint stress in severe moisture conditions. A deck with inadequate spacing and inadequate ventilation will almost certainly buckle. The hierarchy of risk is clear: address both systems, not just one.

Deck Inspection During Re-Roofing

A full tear-off provides the only opportunity to inspect the existing deck panels, assess their moisture content, and correct spacing deficiencies before installing new shingles. 1 Source Roofing's process on every re-roof includes deck inspection as a standard step — not an add-on service. Our crews walk the deck, probe for soft spots, document any areas of delamination or surface deterioration, and measure moisture content with a pin-type moisture meter. Panels with moisture readings above 19% are replaced before shingles are installed, because high-moisture panels will dry and shrink after installation, creating the same joint movement problem as under-spaced panels. See our technical page on roof deck requirements for complete deck assessment criteria.

Georgia-Specific Factors That Accelerate Shingle Buckling

Metro Atlanta's climate creates a specific set of conditions that make shingle buckling more common here than in drier or cooler regions. Understanding those conditions helps homeowners make better decisions about ventilation upgrades, re-roofing timing, and contractor selection.

High Humidity and the Moisture Cycling Problem

Georgia averages 50 to 55 inches of rainfall per year, with humidity running high for most of the year. The combination of warm temperatures and high humidity creates persistent moisture loads in attic air. An attic in metro Atlanta on a typical July afternoon contains air that is both hot — easily 130°F to 150°F in a poorly ventilated space — and humid. That combination drives moisture vapor directly into the roof deck from below. Unlike a cold-climate attic where the moisture concern is winter condensation from heated indoor air, Georgia's moisture problem runs from roughly April through October, covering most of the year.

This extended moisture season means that deck panels in under-ventilated Atlanta attics experience more moisture cycling than equivalent panels in, say, Denver or Phoenix. Each wet-dry cycle contributes to the cumulative expansion and contraction stress that leads to joint movement and buckling. Over a five-to-ten year period on a home with inadequate ventilation, this cycling can cause enough deck deformation to produce visible buckling even if the panels were correctly spaced when installed.

Summer Attic Heat and Panel Temperature

South-facing roof slopes in Georgia receive intense solar loading from late spring through early fall. A dark-colored shingle on a south-facing slope can reach 170°F on the surface during a July afternoon. The OSB panel beneath the shingle does not reach that temperature — the shingle and underlayment provide some thermal buffer — but deck panel temperatures above 120°F are common in the middle of a Georgia summer day. At those temperatures, the thermal expansion of the panel is significant, and the difference in temperature between the hottest part of the day and the coolest part of the night creates expansion and contraction cycling every 24 hours.

This daily cycling, compounded over a Georgia summer, explains why buckled shingles sometimes appear to relax slightly in winter and become more pronounced again in summer. The deck panel is contracting in the cold and expanding in the heat, and the buckle tracks that cycle. A buckle that appears and disappears seasonally is still a buckling problem — the underlying gap deficiency has not corrected itself. It is simply less visible when the temperature differential is lower.

Attic Insulation Upgrades Without Ventilation Review

Over the last fifteen years, many metro Atlanta homeowners have upgraded attic insulation as part of energy efficiency programs. Adding insulation is beneficial, but a significant number of these upgrades were performed without reviewing the ventilation system. Blown-in insulation added on top of existing batt insulation frequently buries the soffit vent openings, eliminating intake ventilation for one or more rafter bays. The result is a home that is better insulated but has worse attic ventilation than it did before — a combination that can trigger moisture-driven buckling on a roof that performed fine for the previous fifteen years.

If you have had attic insulation added in the last ten years and your roof is now showing buckling, the insulation upgrade is a strong candidate for the root cause. An attic inspection that confirms whether soffit baffles are present and whether the vent openings are clear can resolve this question quickly. If the soffit vents are blocked, clearing them and adding baffles is a relatively low-cost correction that can prevent further deck moisture accumulation — though it will not correct deck panels that have already been permanently deformed.

Assessing Buckled Shingles: Replacement or Monitoring?

Not every buckled roof requires immediate full replacement. The appropriate response depends on the severity of the buckling, the age and condition of the shingles, and the root cause. Here is how 1 Source Roofing approaches the assessment during an inspection.

Factors That Support Monitoring

A newly installed roof — less than two years old — with minor buckling at deck joints may be a candidate for monitoring if several conditions are met: the shingles are otherwise in good condition with no cracking or granule loss at the fold points; the attic ventilation has been verified to meet the 1:150 ratio with balanced intake and exhaust; and the homeowner is committed to a follow-up inspection after the first full summer season. In this scenario, the deck panels may still be acclimatizing to the ventilation system, and some shingles may relax to a flatter profile as the deck stabilizes. This is not guaranteed — it is a best-case outcome that applies to a narrow set of conditions.

Monitoring is appropriate only when the buckling is recent, minor, and traceable to a correctable cause that has actually been corrected. A homeowner who has blocked soffit vents unblocked and confirmed adequate airflow has addressed the root cause. Whether the shingles will relax after that correction depends on how long they were buckled and how much permanent deformation has occurred in the fiberglass mat.

Factors That Require Replacement

Replacement is the correct answer when any of the following conditions are present:

• Shingles have been visibly buckled for more than one full seasonal cycle (one summer and winter)
• Cracking is visible at the fold point of the buckle — the shingle mat has already failed at that stress concentration
• The shingle granule layer is depleted at the ridge of the buckle, exposing the asphalt mat to UV
• The roof is more than 15 years old and shows combined buckling and curling — end-of-life signs
• Moisture has entered the roof system at the buckle location, evidenced by staining on the deck, underlayment damage, or interior leak signs
• The buckling is widespread across multiple slopes, indicating a systemic deck or ventilation problem that cannot be addressed without full tear-off

When replacement is warranted, the decision also determines the scope of the re-roofing project. If the deck panels are the source of the problem, a layer-over installation is not appropriate — full tear-off and deck inspection are required. If the existing deck is in good condition with correctly spaced panels and the buckling was caused by inadequate ventilation that has since been corrected, a layer-over may be acceptable if the existing shingle layer is flat. But given that buckling shingles are by definition not flat, a layer-over will produce a finished roof that telegraphs the existing irregularities. Full tear-off gives the best result in every buckling scenario. For more information on what the repair process involves, see our roof repair services page.

The 1 Source Roofing Inspection Process

When 1 Source Roofing is called to inspect a home with suspected shingle buckling, the inspection covers five components:

• Visual pattern mapping: We document the buckle locations, orientation, and pattern to determine whether they correspond to deck joints, and whether the pattern is consistent with a spacing issue, a ventilation issue, or wet-deck installation.
• Attic entry and ventilation assessment: We enter the attic, measure the actual ventilation area, confirm that soffit and ridge vents are unobstructed, and check for signs of condensation or moisture damage on the deck underside.
• Moisture meter readings: We take pin-type moisture readings at representative deck panel locations to assess current moisture content.
• Shingle condition assessment: We assess granule retention, tab condition, cracking at fold points, and overall age-related deterioration to determine whether the shingles have sufficient remaining life to warrant monitoring rather than replacement.
• Written findings and recommendation: We provide a written summary of findings, the most likely root cause, and a specific recommendation — replacement now, monitoring with re-inspection in 12 months, or ventilation correction with re-inspection. We do not provide a one-size-fits-all answer because buckling diagnoses are not one-size-fits-all problems.

If you see ridge lines on your roof — straight, running up the slope or across the slope — call us at (404) 277-1377 to schedule a free inspection. We will tell you exactly what we find.

Technical Bulletins from GAF and CertainTeed

The information on this page is backed by official manufacturer technical bulletins. These documents provide the installation specifications, warranty requirements, and best practices that certified contractors like 1 Source Roofing follow on every project.

• CertainTeed — Asphalt Shingle Buckling Technical Bulletin (PDF)